86Box/src/nvr_at.c

/*
 * 86Box    A hypervisor and IBM PC system emulator that specializes in
 *          running old operating systems and software designed for IBM
 *          PC systems and compatibles from 1981 through fairly recent
 *          system designs based on the PCI bus.
 *
 *          This file is part of the 86Box distribution.
 *
 *          Implement a more-or-less defacto-standard RTC/NVRAM.
 *
 *          When IBM released the PC/AT machine, it came standard with a
 *          battery-backed RTC chip to keep the time of day, something
 *          that was optional on standard PC's with a myriad variants
 *          being put on the market, often on cheap multi-I/O cards.
 *
 *          The PC/AT had an on-board DS12885-series chip ("the black
 *          block") which was an RTC/clock chip with onboard oscillator
 *          and a backup battery (hence the big size.) The chip also had
 *          a small amount of RAM bytes available to the user, which was
 *          used by IBM's ROM BIOS to store machine configuration data.
 *          Later versions and clones used the 12886 and/or 1288(C)7
 *          series, or the MC146818 series, all with an external battery.
 *          Many of those batteries would create corrosion issues later
 *          on in mainboard life...
 *
 *          Since then, pretty much any PC has an implementation of that
 *          device, which became known as the "nvr" or "cmos".
 *
 * NOTES    Info extracted from the data sheets:
 *
 *          * The century register at location 32h is a BCD register
 *            designed to automatically load the BCD value 20 as the
 *            year register changes from 99 to 00.  The MSB of this
 *            register is not affected when the load of 20 occurs,
 *            and remains at the value written by the user.
 *
 *          * Rate Selector (RS3:RS0)
 *            These four rate-selection bits select one of the 13
 *            taps on the 15-stage divider or disable the divider
 *            output.  The tap selected can be used to generate an
 *            output square wave (SQW pin) and/or a periodic interrupt.
 *
 *            The user can do one of the following:
 *             - enable the interrupt with the PIE bit;
 *             - enable the SQW output pin with the SQWE bit;
 *             - enable both at the same time and the same rate; or
 *             - enable neither.
 *
 *            Table 3 lists the periodic interrupt rates and the square
 *            wave frequencies that can be chosen with the RS bits.
 *            These four read/write bits are not affected by !RESET.
 *
 *          * Oscillator (DV2:DV0)
 *            These three bits are used to turn the oscillator on or
 *            off and to reset the countdown chain.  A pattern of 010
 *            is the only combination of bits that turn the oscillator
 *            on and allow the RTC to keep time.  A pattern of 11x
 *            enables the oscillator but holds the countdown chain in
 *            reset.  The next update occurs at 500ms after a pattern
 *            of 010 is written to DV0, DV1, and DV2.
 *
 *          * Update-In-Progress (UIP)
 *            This bit is a status flag that can be monitored. When the
 *            UIP bit is a 1, the update transfer occurs soon.  When
 *            UIP is a 0, the update transfer does not occur for at
 *            least 244us.  The time, calendar, and alarm information
 *            in RAM is fully available for access when the UIP bit
 *            is 0.  The UIP bit is read-only and is not affected by
 *            !RESET.  Writing the SET bit in Register B to a 1
 *            inhibits any update transfer and clears the UIP status bit.
 *
 *          * Daylight Saving Enable (DSE)
 *            This bit is a read/write bit that enables two daylight
 *            saving adjustments when DSE is set to 1.  On the first
 *            Sunday in April (or the last Sunday in April in the
 *            MC146818A), the time increments from 1:59:59 AM to
 *            3:00:00 AM.  On the last Sunday in October when the time
 *            first reaches 1:59:59 AM, it changes to 1:00:00 AM.
 *
 *            When DSE is enabled, the internal logic test for the
 *            first/last Sunday condition at midnight.  If the DSE bit
 *            is not set when the test occurs, the daylight saving
 *            function does not operate correctly.  These adjustments
 *            do not occur when the DSE bit is 0. This bit is not
 *            affected by internal functions or !RESET.
 *
 *          * 24/12
 *            The 24/12 control bit establishes the format of the hours
 *            byte. A 1 indicates the 24-hour mode and a 0 indicates
 *            the 12-hour mode.  This bit is read/write and is not
 *            affected by internal functions or !RESET.
 *
 *          * Data Mode (DM)
 *            This bit indicates whether time and calendar information
 *            is in binary or BCD format.  The DM bit is set by the
 *            program to the appropriate format and can be read as
 *            required.  This bit is not modified by internal functions
 *            or !RESET. A 1 in DM signifies binary data, while a 0 in
 *            DM specifies BCD data.
 *
 *          * Square-Wave Enable (SQWE)
 *            When this bit is set to 1, a square-wave signal at the
 *            frequency set by the rate-selection bits RS3-RS0 is driven
 *            out on the SQW pin.  When the SQWE bit is set to 0, the
 *            SQW pin is held low. SQWE is a read/write bit and is
 *            cleared by !RESET.  SQWE is low if disabled, and is high
 *            impedance when VCC is below VPF. SQWE is cleared to 0 on
 *            !RESET.
 *
 *          * Update-Ended Interrupt Enable (UIE)
 *            This bit is a read/write bit that enables the update-end
 *            flag (UF) bit in Register C to assert !IRQ.  The !RESET
 *            pin going low or the SET bit going high clears the UIE bit.
 *            The internal functions of the device do not affect the UIE
 *            bit, but is cleared to 0 on !RESET.
 *
 *          * Alarm Interrupt Enable (AIE)
 *            This bit is a read/write bit that, when set to 1, permits
 *            the alarm flag (AF) bit in Register C to assert !IRQ.  An
 *            alarm interrupt occurs for each second that the three time
 *            bytes equal the three alarm bytes, including a don't-care
 *            alarm code of binary 11XXXXXX.  The AF bit does not
 *            initiate the !IRQ signal when the AIE bit is set to 0.
 *            The internal functions of the device do not affect the AIE
 *            bit, but is cleared to 0 on !RESET.
 *
 *          * Periodic Interrupt Enable (PIE)
 *            The PIE bit is a read/write bit that allows the periodic
 *            interrupt flag (PF) bit in Register C to drive the !IRQ pin
 *            low.  When the PIE bit is set to 1, periodic interrupts are
 *            generated by driving the !IRQ pin low at a rate specified
 *            by the RS3-RS0 bits of Register A.  A 0 in the PIE bit
 *            blocks the !IRQ output from being driven by a periodic
 *            interrupt, but the PF bit is still set at the periodic
 *            rate.  PIE is not modified b any internal device functions,
 *            but is cleared to 0 on !RESET.
 *
 *          * SET
 *            When the SET bit is 0, the update transfer functions
 *            normally by advancing the counts once per second.  When
 *            the SET bit is written to 1, any update transfer is
 *            inhibited, and the program can initialize the time and
 *            calendar bytes without an update occurring in the midst of
 *            initializing. Read cycles can be executed in a similar
 *            manner. SET is a read/write bit and is not affected by
 *            !RESET or internal functions of the device.
 *
 *          * Update-Ended Interrupt Flag (UF)
 *            This bit is set after each update cycle. When the UIE
 *            bit is set to 1, the 1 in UF causes the IRQF bit to be
 *            a 1, which asserts the !IRQ pin.  This bit can be
 *            cleared by reading Register C or with a !RESET.
 *
 *          * Alarm Interrupt Flag (AF)
 *            A 1 in the AF bit indicates that the current time has
 *            matched the alarm time.  If the AIE bit is also 1, the
 *            !IRQ pin goes low and a 1 appears in the IRQF bit. This
 *            bit can be cleared by reading Register C or with a
 *            !RESET.
 *
 *          * Periodic Interrupt Flag (PF)
 *            This bit is read-only and is set to 1 when an edge is
 *            detected on the selected tap of the divider chain.  The
 *            RS3 through RS0 bits establish the periodic rate. PF is
 *            set to 1 independent of the state of the PIE bit.  When
 *            both PF and PIE are 1s, the !IRQ signal is active and
 *            sets the IRQF bit. This bit can be cleared by reading
 *            Register C or with a !RESET.
 *
 *          * Interrupt Request Flag (IRQF)
 *            The interrupt request flag (IRQF) is set to a 1 when one
 *            or more of the following are true:
 *             - PF == PIE == 1
 *             - AF == AIE == 1
 *             - UF == UIE == 1
 *            Any time the IRQF bit is a 1, the !IRQ pin is driven low.
 *            All flag bits are cleared after Register C is read by the
 *            program or when the !RESET pin is low.
 *
 *          * Valid RAM and Time (VRT)
 *            This bit indicates the condition of the battery connected
 *            to the VBAT pin. This bit is not writeable and should
 *            always be 1 when read.  If a 0 is ever present, an
 *            exhausted internal lithium energy source is indicated and
 *            both the contents of the RTC data and RAM data are
 *            questionable.  This bit is unaffected by !RESET.
 *
 *          This file implements a generic version of the RTC/NVRAM chip,
 *          including the later update (DS12887A) which implemented a
 *          "century" register to be compatible with Y2K.
 *
 *
 *
 * Authors: Fred N. van Kempen, <decwiz@yahoo.com>
 *          Miran Grca, <mgrca8@gmail.com>
 *          Mahod,
 *
 *          Copyright 2017-2020 Fred N. van Kempen.
 *          Copyright 2016-2020 Miran Grca.
 *          Copyright 2016-2020 Mahod.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free  Software  Foundation; either  version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is  distributed in the hope that it will be useful, but
 * WITHOUT   ANY  WARRANTY;  without  even   the  implied  warranty  of
 * MERCHANTABILITY  or FITNESS  FOR A PARTICULAR  PURPOSE. See  the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the:
 *
 *   Free Software Foundation, Inc.
 *   59 Temple Place - Suite 330
 *   Boston, MA 02111-1307
 *   USA.
 */
#include <inttypes.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdlib.h>
#include <wchar.h>
#include <time.h>
#include <86box/86box.h>
#include "cpu.h"
#include <86box/machine.h>
#include <86box/io.h>
#include <86box/mem.h>
#include <86box/nmi.h>
#include <86box/pic.h>
#include <86box/timer.h>
#include <86box/pit.h>
#include <86box/rom.h>
#include <86box/device.h>
#include <86box/nvr.h>

/* RTC registers and bit definitions. */
#define RTC_SECONDS        0
#define RTC_ALSECONDS      1
#define AL_DONTCARE        0xc0 /* Alarm time is not set */
#define RTC_MINUTES        2
#define RTC_ALMINUTES      3
#define RTC_HOURS          4
#define RTC_AMPM           0x80 /* PM flag if 12h format in use */
#define RTC_ALHOURS        5
#define RTC_DOW            6
#define RTC_DOM            7
#define RTC_MONTH          8
#define RTC_YEAR           9
#define RTC_REGA           10
#define REGA_UIP           0x80
#define REGA_DV2           0x40
#define REGA_DV1           0x20
#define REGA_DV0           0x10
#define REGA_DV            0x70
#define REGA_RS3           0x08
#define REGA_RS2           0x04
#define REGA_RS1           0x02
#define REGA_RS0           0x01
#define REGA_RS            0x0f
#define RTC_REGB           11
#define REGB_SET           0x80
#define REGB_PIE           0x40
#define REGB_AIE           0x20
#define REGB_UIE           0x10
#define REGB_SQWE          0x08
#define REGB_DM            0x04
#define REGB_2412          0x02
#define REGB_DSE           0x01
#define RTC_REGC           12
#define REGC_IRQF          0x80
#define REGC_PF            0x40
#define REGC_AF            0x20
#define REGC_UF            0x10
#define RTC_REGD           13
#define REGD_VRT           0x80
#define RTC_CENTURY_AT     0x32 /* century register for AT etc */
#define RTC_CENTURY_PS     0x37 /* century register for PS/1 PS/2 */
#define RTC_CENTURY_ELT    0x1A /* century register for Epson Equity LT */
#define RTC_ALDAY          0x7D /* VIA VT82C586B - alarm day */
#define RTC_ALMONTH        0x7E /* VIA VT82C586B - alarm month */
#define RTC_CENTURY_VIA    0x7F /* century register for VIA VT82C586B */

#define RTC_ALDAY_SIS      0x7E /* Day of Month Alarm for SiS */
#define RTC_ALMONT_SIS     0x7F /* Month Alarm for SiS */

#define RTC_REGS           14 /* number of registers */

#define FLAG_NO_NMI        0x01
#define FLAG_AMI_1992_HACK 0x02
#define FLAG_AMI_1994_HACK 0x04
#define FLAG_AMI_1995_HACK 0x08
#define FLAG_P6RP4_HACK    0x10
#define FLAG_PIIX4         0x20
#define FLAG_MULTI_BANK    0x40
#define FLAG_MARTIN_HACK   0x80

typedef struct local_t {
    int8_t stat;

    uint8_t cent;
    uint8_t def;
    uint8_t flags;
    uint8_t read_addr;
    uint8_t wp_0d;
    uint8_t wp_32;
    uint8_t irq_state;
    uint8_t smi_status;

    uint8_t  wp[2];
    uint8_t  bank[8];
    uint8_t *lock;

    int16_t count;
    int16_t state;

    uint16_t  addr[8];

    int32_t smi_enable;

    uint64_t   ecount;
    uint64_t   rtc_time;
    pc_timer_t update_timer;
    pc_timer_t rtc_timer;
} local_t;

static uint8_t nvr_at_inited = 0;

/* Get the current NVR time. */
static void
time_get(nvr_t *nvr, struct tm *tm)
{
    const local_t *local = (local_t *) nvr->data;
    int8_t         temp;

    if (nvr->regs[RTC_REGB] & REGB_DM) {
        /* NVR is in Binary data mode. */
        tm->tm_sec  = nvr->regs[RTC_SECONDS];
        tm->tm_min  = nvr->regs[RTC_MINUTES];
        temp        = nvr->regs[RTC_HOURS];
        tm->tm_wday = (nvr->regs[RTC_DOW] - 1);
        tm->tm_mday = nvr->regs[RTC_DOM];
        tm->tm_mon  = (nvr->regs[RTC_MONTH] - 1);
        tm->tm_year = nvr->regs[RTC_YEAR];
        if (local->cent != 0xFF)
            tm->tm_year += (nvr->regs[local->cent] * 100) - 1900;
    } else {
        /* NVR is in BCD data mode. */
        tm->tm_sec  = RTC_DCB(nvr->regs[RTC_SECONDS]);
        tm->tm_min  = RTC_DCB(nvr->regs[RTC_MINUTES]);
        temp        = RTC_DCB(nvr->regs[RTC_HOURS]);
        tm->tm_wday = (RTC_DCB(nvr->regs[RTC_DOW]) - 1);
        tm->tm_mday = RTC_DCB(nvr->regs[RTC_DOM]);
        tm->tm_mon  = (RTC_DCB(nvr->regs[RTC_MONTH]) - 1);
        tm->tm_year = RTC_DCB(nvr->regs[RTC_YEAR]);
        if (local->cent != 0xFF)
            tm->tm_year += (RTC_DCB(nvr->regs[local->cent]) * 100) - 1900;
    }

    /* Adjust for 12/24 hour mode. */
    if (nvr->regs[RTC_REGB] & REGB_2412)
        tm->tm_hour = temp;
    else
        tm->tm_hour = ((temp & ~RTC_AMPM) % 12) + ((temp & RTC_AMPM) ? 12 : 0);
}

/* Set the current NVR time. */
static void
time_set(nvr_t *nvr, struct tm *tm)
{
    const local_t *local = (local_t *) nvr->data;
    int            year  = (tm->tm_year + 1900);

    if (nvr->regs[RTC_REGB] & REGB_DM) {
        /* NVR is in Binary data mode. */
        nvr->regs[RTC_SECONDS] = tm->tm_sec;
        nvr->regs[RTC_MINUTES] = tm->tm_min;
        nvr->regs[RTC_DOW]     = (tm->tm_wday + 1);
        nvr->regs[RTC_DOM]     = tm->tm_mday;
        nvr->regs[RTC_MONTH]   = (tm->tm_mon + 1);
        nvr->regs[RTC_YEAR]    = (year % 100);
        if (local->cent != 0xFF)
            nvr->regs[local->cent] = (year / 100);

        if (nvr->regs[RTC_REGB] & REGB_2412) {
            /* NVR is in 24h mode. */
            nvr->regs[RTC_HOURS] = tm->tm_hour;
        } else {
            /* NVR is in 12h mode. */
            nvr->regs[RTC_HOURS] = (tm->tm_hour % 12) ? (tm->tm_hour % 12) : 12;
            if (tm->tm_hour > 11)
                nvr->regs[RTC_HOURS] |= RTC_AMPM;
        }
    } else {
        /* NVR is in BCD data mode. */
        nvr->regs[RTC_SECONDS] = RTC_BCD(tm->tm_sec);
        nvr->regs[RTC_MINUTES] = RTC_BCD(tm->tm_min);
        nvr->regs[RTC_DOW]     = RTC_BCD(tm->tm_wday + 1);
        nvr->regs[RTC_DOM]     = RTC_BCD(tm->tm_mday);
        nvr->regs[RTC_MONTH]   = RTC_BCD(tm->tm_mon + 1);
        nvr->regs[RTC_YEAR]    = RTC_BCD(year % 100);
        if (local->cent != 0xFF)
            nvr->regs[local->cent] = RTC_BCD(year / 100);

        if (nvr->regs[RTC_REGB] & REGB_2412) {
            /* NVR is in 24h mode. */
            nvr->regs[RTC_HOURS] = RTC_BCD(tm->tm_hour);
        } else {
            /* NVR is in 12h mode. */
            nvr->regs[RTC_HOURS] = (tm->tm_hour % 12)
                ? RTC_BCD(tm->tm_hour % 12)
                : RTC_BCD(12);
            if (tm->tm_hour > 11)
                nvr->regs[RTC_HOURS] |= RTC_AMPM;
        }
    }
}

/* Check if the current time matches a set alarm time. */
static int8_t
check_alarm(nvr_t *nvr, int8_t addr)
{
    return ((nvr->regs[addr + 1] == nvr->regs[addr]) || ((nvr->regs[addr + 1] & AL_DONTCARE) == AL_DONTCARE));
}

/* Check for VIA stuff. */
static int8_t
check_alarm_via(nvr_t *nvr, int8_t addr, int8_t addr_2)
{
    const local_t *local = (local_t *) nvr->data;

    if (local->cent == RTC_CENTURY_VIA) {
        return ((nvr->regs[addr_2] == nvr->regs[addr]) || ((nvr->regs[addr_2] & AL_DONTCARE) == AL_DONTCARE));
    } else
        return 1;
}

static void
timer_update_irq(nvr_t *nvr)
{
    local_t *local = (local_t *) nvr->data;
    uint8_t irq = (nvr->regs[RTC_REGB] & nvr->regs[RTC_REGC]) & (REGB_UIE | REGB_AIE | REGB_PIE);

    if (irq || (local->irq_state != !!irq)) {
        if (irq) {
            nvr->regs[RTC_REGC] |= REGC_IRQF;
            picintlevel(1 << nvr->irq, &local->irq_state);
            if (local->smi_enable) {
                smi_raise();
                local->smi_status = 1;
            }
        } else {
            nvr->regs[RTC_REGC] &= ~REGC_IRQF;
            picintclevel(1 << nvr->irq, &local->irq_state);
        }
    }
}

/* Update the NVR registers from the internal clock. */
static void
timer_update(void *priv)
{
    nvr_t    *nvr   = (nvr_t *) priv;
    local_t  *local = (local_t *) nvr->data;
    struct tm tm;

    if (local->ecount == (244ULL * TIMER_USEC)) {
        rtc_tick();

        /* Get the current time from the internal clock. */
        nvr_time_get(&tm);

        /* Update registers with current time. */
        time_set(nvr, &tm);

        /* Check for any alarms we need to handle. */
        if (check_alarm(nvr, RTC_SECONDS) && check_alarm(nvr, RTC_MINUTES) && check_alarm(nvr, RTC_HOURS) &&
            check_alarm_via(nvr, RTC_DOM, RTC_ALDAY) && check_alarm_via(nvr, RTC_MONTH, RTC_ALMONTH) /* &&
            check_alarm_via(nvr, RTC_DOM, RTC_ALDAY_SIS) && check_alarm_via(nvr, RTC_MONTH, RTC_ALMONT_SIS) */) {
            nvr->regs[RTC_REGC] |= REGC_AF;
            timer_update_irq(nvr);
        }

        /* Schedule the end of the update. */
        local->ecount = 1984ULL * TIMER_USEC;
        timer_set_delay_u64(&local->update_timer, local->ecount);
    } else {
        /*
         * The flag and interrupt should be issued
         * on update ended, not started.
         */
        nvr->regs[RTC_REGC] |= REGC_UF;
        timer_update_irq(nvr);

        /* Clear update status. */
        local->stat = 0x00;

        local->ecount = 0LL;
    }
}

static void
timer_load_count(nvr_t *nvr)
{
    int      c     = nvr->regs[RTC_REGA] & REGA_RS;
    local_t *local = (local_t *) nvr->data;

    timer_disable(&local->rtc_timer);

    if ((nvr->regs[RTC_REGA] & 0x70) != 0x20) {
        local->state = 0;
        return;
    }

    local->state = 1;

    switch (c) {
        case 0:
            local->state = 0;
            break;
        case 1:
        case 2:
            local->count = 1 << (c + 6);
            timer_set_delay_u64(&local->rtc_timer, (local->count) * RTCCONST);
            break;
        default:
            local->count = 1 << (c - 1);
            timer_set_delay_u64(&local->rtc_timer, (local->count) * RTCCONST);
            break;
    }
}

static void
timer_intr(void *priv)
{
    nvr_t         *nvr   = (nvr_t *) priv;
    const local_t *local = (local_t *) nvr->data;

    if (local->state == 1) {
        timer_load_count(nvr);

        nvr->regs[RTC_REGC] |= REGC_PF;
        timer_update_irq(nvr);
    }
}

/* Callback from internal clock, another second passed. */
static void
timer_tick(nvr_t *nvr)
{
    local_t *local = (local_t *) nvr->data;

    /* Only update it there is no SET in progress.
       Also avoid updating it is DV2-DV0 are not set to 0, 1, 0. */
    if (((nvr->regs[RTC_REGA] & 0x70) == 0x20) && !(nvr->regs[RTC_REGB] & REGB_SET)) {
        /* Set the UIP bit, announcing the update. */
        local->stat = REGA_UIP;

        /* Schedule the actual update. */
        local->ecount = 244ULL * TIMER_USEC;
        timer_set_delay_u64(&local->update_timer, local->ecount);
    }
}

static void
nvr_reg_common_write(uint16_t reg, uint8_t val, nvr_t *nvr, local_t *local)
{
    if (local->lock[reg])
        return;
    if ((reg == 0x2c) && (local->flags & FLAG_AMI_1994_HACK))
        nvr->is_new = 0;
    if ((reg == 0x2d) && (local->flags & FLAG_AMI_1992_HACK))
        nvr->is_new = 0;
    if ((reg == 0x52) && (local->flags & FLAG_AMI_1995_HACK))
        nvr->is_new = 0;
    if ((reg >= 0x38) && (reg <= 0x3f) && local->wp[0])
        return;
    if ((reg >= 0xb8) && (reg <= 0xbf) && local->wp[1])
        return;
    if (nvr->regs[reg] != val) {
        nvr->regs[reg] = val;
        if ((reg >= 0x0d) && ((local->cent == 0xff) || (reg != local->cent)))
            nvr_dosave     = 1;
    }
}

/* This must be exposed because ACPI uses it. */
void
nvr_reg_write(uint16_t reg, uint8_t val, void *priv)
{
    nvr_t    *nvr   = (nvr_t *) priv;
    local_t  *local = (local_t *) nvr->data;
    struct tm tm;
    uint8_t   old;

    old = nvr->regs[reg];
    switch (reg) {
        case RTC_SECONDS: /* bit 7 of seconds is read-only */
            nvr_reg_common_write(reg, val & 0x7f, nvr, local);
            break;

        case RTC_REGA:
            if ((val & nvr->regs[RTC_REGA]) & ~REGA_UIP) {
                nvr->regs[RTC_REGA] = (nvr->regs[RTC_REGA] & REGA_UIP) | (val & ~REGA_UIP);
                timer_load_count(nvr);
            }
            break;

        case RTC_REGB:
            if (((old ^ val) & REGB_SET) && (val & REGB_SET)) {
                /* According to the datasheet... */
                val &= ~REGB_UIE;
                local->stat &= ~REGA_UIP;
            }

            nvr->regs[RTC_REGB] = val;
            timer_update_irq(nvr);
            break;

        case RTC_REGC: /* R/O */
            break;

        case RTC_REGD: /* R/O */
            /* This is needed for VIA, where writing to this register changes a write-only
               bit whose value is read from power management register 42. */
            nvr->regs[RTC_REGD] = val & 0x80;
            break;

        case 0x32:
            if ((reg == 0x32) && (local->cent == RTC_CENTURY_VIA) && local->wp_32)
                break;
            nvr_reg_common_write(reg, val, nvr, local);
            break;

        default: /* non-RTC registers are just NVRAM */
            nvr_reg_common_write(reg, val, nvr, local);
            break;
    }

    if ((reg < RTC_REGA) || ((local->cent != 0xff) && (reg == local->cent))) {
        if ((reg != 1) && (reg != 3) && (reg != 5)) {
            if ((old != val) && !(time_sync & TIME_SYNC_ENABLED)) {
                /* Update internal clock. */
                time_get(nvr, &tm);
                nvr_time_set(&tm);
                // nvr_dosave = 1;
            }
        }
    }
}

/* Write to one of the NVR registers. */
static void
nvr_write(uint16_t addr, uint8_t val, void *priv)
{
    nvr_t   *nvr     = (nvr_t *) priv;
    local_t *local   = (local_t *) nvr->data;
    uint8_t  addr_id = (addr & 0x0e) >> 1;

    cycles -= ISA_CYCLES(8);

    if (local->bank[addr_id] == 0xff)
        return;

    if (addr & 1) {
#if 0
        if (local->bank[addr_id] == 0xff)
            return;
#endif
        nvr_reg_write(local->addr[addr_id], val, priv);
    } else {
        local->addr[addr_id] = (val & (nvr->size - 1));
        /* Some chipsets use a 256 byte NVRAM but ports 70h and 71h always access only 128 bytes. */
        if (addr_id == 0x0) {
            local->addr[addr_id] &= 0x7f;
            /* Needed for OPTi 82C601/82C602 and NSC PC87306. */
            if (local->flags & FLAG_MULTI_BANK)
                local->addr[addr_id] |= (0x80 * local->bank[addr_id]);
        } else if ((addr_id == 0x1) && (local->flags & FLAG_PIIX4))
            local->addr[addr_id] = (local->addr[addr_id] & 0x7f) | 0x80;
        if (local->bank[addr_id] > 0)
            local->addr[addr_id] = (local->addr[addr_id] & 0x7f) | (0x80 * local->bank[addr_id]);
        if (!(local->flags & FLAG_NO_NMI))
            nmi_mask = (~val & 0x80);
    }
}

/* Get the NVR register index (used for APC). */
uint8_t
nvr_get_index(void *priv, uint8_t addr_id)
{
    nvr_t   *nvr     = (nvr_t *) priv;
    local_t *local   = (local_t *) nvr->data;
    uint8_t  ret;

    ret = local->addr[addr_id];

    return ret;
}

/* Read from one of the NVR registers. */
static uint8_t
nvr_read(uint16_t addr, void *priv)
{
    nvr_t         *nvr   = (nvr_t *) priv;
    const local_t *local = (local_t *) nvr->data;
    uint8_t        ret = 0xff;
    uint8_t        addr_id = (addr & 0x0e) >> 1;
    uint16_t       i;
    uint16_t       checksum = 0x0000;

    cycles -= ISA_CYCLES(8);

    if (local->bank[addr_id] == 0xff)
        ret = 0xff;
    else if (addr & 1)
        switch (local->addr[addr_id]) {
            case RTC_REGA:
                ret = (nvr->regs[RTC_REGA] & 0x7f) | local->stat;
                break;

            case RTC_REGC:
                ret = nvr->regs[RTC_REGC] & (REGC_IRQF | REGC_PF | REGC_AF | REGC_UF);
                nvr->regs[RTC_REGC] &= ~(REGC_IRQF | REGC_PF | REGC_AF | REGC_UF);
                timer_update_irq(nvr);
                break;

            case RTC_REGD:
                /* Bits 6-0 of this register always read 0. Bit 7 is battery state,
                   we should always return it set, as that means the battery is OK. */
                ret = REGD_VRT;
                break;

            case 0x11:
                if (local->flags & FLAG_MARTIN_HACK)
                    ret = nvr->regs[local->addr[addr_id]] | 0x02;
                else
                    ret = nvr->regs[local->addr[addr_id]];
                break;

            case 0x2c:
                if (!nvr->is_new && (local->flags & FLAG_AMI_1994_HACK))
                    ret = nvr->regs[local->addr[addr_id]] & 0x7f;
                else
                    ret = nvr->regs[local->addr[addr_id]];
                break;

            case 0x2d:
                if (!nvr->is_new && (local->flags & FLAG_AMI_1992_HACK))
                    ret = nvr->regs[local->addr[addr_id]] & 0xf7;
                else
                    ret = nvr->regs[local->addr[addr_id]];
                break;

            case 0x2e:
            case 0x2f:
                if (!nvr->is_new && (local->flags & FLAG_AMI_1992_HACK)) {
                    for (i = 0x10; i <= 0x2d; i++) {
                        if (i == 0x2d)
                            checksum += (nvr->regs[i] & 0xf7);
                        else
                            checksum += nvr->regs[i];
                    }
                    if (local->addr[addr_id] == 0x2e)
                        ret = checksum >> 8;
                    else
                        ret = checksum & 0xff;
                } else if (!nvr->is_new && (local->flags & FLAG_AMI_1994_HACK)) {
                    for (i = 0x10; i <= 0x2d; i++) {
                        if (i == 0x2c)
                            checksum += (nvr->regs[i] & 0x7f);
                        else
                            checksum += nvr->regs[i];
                    }
                    if (local->addr[addr_id] == 0x2e)
                        ret = checksum >> 8;
                    else
                        ret = checksum & 0xff;
                } else if (!nvr->is_new && (local->flags & FLAG_MARTIN_HACK)) {
                    for (i = 0x10; i <= 0x2d; i++) {
                        if (i == 0x11)
                            checksum += (nvr->regs[i] | 0x02);
                        else
                            checksum += nvr->regs[i];
                    }
                    if (local->addr[addr_id] == 0x2e)
                        ret = checksum >> 8;
                    else
                        ret = checksum & 0xff;
                } else
                    ret = nvr->regs[local->addr[addr_id]];
                break;

            case 0x3e:
            case 0x3f:
                if (!nvr->is_new && (local->flags & FLAG_AMI_1995_HACK)) {
                    /* The checksum at 3E-3F is for 37-3D and 40-7F. */
                    for (i = 0x37; i <= 0x3d; i++)
                        checksum += nvr->regs[i];
                    for (i = 0x40; i <= 0x7f; i++) {
                        if (i == 0x52)
                            checksum += (nvr->regs[i] & 0xf3);
                        else
                            checksum += nvr->regs[i];
                    }
                    if (local->addr[addr_id] == 0x3e)
                        ret = checksum >> 8;
                    else
                        ret = checksum & 0xff;
                } else if (!nvr->is_new && (local->flags & FLAG_P6RP4_HACK)) {
                    /* The checksum at 3E-3F is for 37-3D and 40-51. */
                    for (i = 0x37; i <= 0x3d; i++)
                        checksum += nvr->regs[i];
                    for (i = 0x40; i <= 0x51; i++) {
                        if (i == 0x43)
                            checksum += (nvr->regs[i] | 0x02);
                        else
                            checksum += nvr->regs[i];
                    }
                    if (local->addr[addr_id] == 0x3e)
                        ret = checksum >> 8;
                    else
                        ret = checksum & 0xff;
                } else
                    ret = nvr->regs[local->addr[addr_id]];
                break;

            case 0x43:
                if (!nvr->is_new && (local->flags & FLAG_P6RP4_HACK))
                    ret = nvr->regs[local->addr[addr_id]] | 0x02;
                else
                    ret = nvr->regs[local->addr[addr_id]];
                break;

            case 0x52:
                if (!nvr->is_new && (local->flags & FLAG_AMI_1995_HACK))
                    ret = nvr->regs[local->addr[addr_id]] & 0xf3;
                else
                    ret = nvr->regs[local->addr[addr_id]];
                break;

            default:
                if (!(local->lock[local->addr[addr_id]] & 0x02))
                    ret = nvr->regs[local->addr[addr_id]];
                break;
        }
    else {
        ret = local->addr[addr_id];
        if (!local->read_addr)
            ret &= 0x80;
        if (alt_access)
            ret = (ret & 0x7f) | (nmi_mask ? 0x00 : 0x80);
    }

    return ret;
}

/* Secondary NVR write - used by SMC. */
static void
nvr_sec_write(uint16_t addr, uint8_t val, void *priv)
{
    nvr_write(0x72 + (addr & 1), val, priv);
}

/* Secondary NVR read - used by SMC. */
static uint8_t
nvr_sec_read(uint16_t addr, void *priv)
{
    return nvr_read(0x72 + (addr & 1), priv);
}

/* Reset the RTC state to 1980/01/01 00:00. */
static void
nvr_reset(nvr_t *nvr)
{
    const local_t *local = (local_t *) nvr->data;

#if 0
    memset(nvr->regs, local->def, RTC_REGS);
#endif
    memset(nvr->regs, local->def, nvr->size);
    nvr->regs[RTC_DOM]   = 1;
    nvr->regs[RTC_MONTH] = 1;
    nvr->regs[RTC_YEAR]  = RTC_BCD(80);
    if (local->cent != 0xFF)
        nvr->regs[local->cent] = RTC_BCD(19);

    nvr->regs[RTC_REGD] = REGD_VRT;
}

/* Process after loading from file. */
static void
nvr_start(nvr_t *nvr)
{
    const local_t *local = (local_t *) nvr->data;

    struct tm tm;
    int       default_found = 0;

    for (uint16_t i = 0; i < nvr->size; i++) {
        if (nvr->regs[i] == local->def)
            default_found++;
    }

    if (default_found == nvr->size)
        nvr->regs[0x0e] = 0xff; /* If load failed or it loaded an uninitialized NVR,
                                   mark everything as bad. */

    /* Initialize the internal and chip times. */
    if (time_sync & TIME_SYNC_ENABLED) {
        /* Use the internal clock's time. */
        nvr_time_get(&tm);
        time_set(nvr, &tm);
    } else {
        /* Set the internal clock from the chip time. */
        time_get(nvr, &tm);
        nvr_time_set(&tm);
    }

    /* Start the RTC. */
    nvr->regs[RTC_REGA] = (REGA_RS2 | REGA_RS1);
    nvr->regs[RTC_REGB] = REGB_2412;
}

static void
nvr_at_speed_changed(void *priv)
{
    nvr_t   *nvr   = (nvr_t *) priv;
    local_t *local = (local_t *) nvr->data;

    timer_load_count(nvr);

    timer_disable(&local->update_timer);
    if (local->ecount > 0ULL)
        timer_set_delay_u64(&local->update_timer, local->ecount);

    timer_disable(&nvr->onesec_time);
    timer_set_delay_u64(&nvr->onesec_time, (10000ULL * TIMER_USEC));
}

void
nvr_at_handler(int set, uint16_t base, nvr_t *nvr)
{
    io_handler(set, base, 2,
               nvr_read, NULL, NULL, nvr_write, NULL, NULL, nvr);
}

void
nvr_at_index_read_handler(int set, uint16_t base, nvr_t *nvr)
{
    io_handler(0, base, 1,
               NULL, NULL, NULL, nvr_write, NULL, NULL, nvr);
    nvr_at_handler(0, base, nvr);

    if (set)
        nvr_at_handler(1, base, nvr);
    else {
        io_handler(1, base, 1,
                   NULL, NULL, NULL, nvr_write, NULL, NULL, nvr);
        io_handler(1, base + 1, 1,
                   nvr_read, NULL, NULL, nvr_write, NULL, NULL, nvr);
    }
}

void
nvr_at_data_port(int set, nvr_t *nvr)
{
    io_handler(0, 0x71, 1,
               nvr_read, NULL, NULL, nvr_write, NULL, NULL, nvr);

    if (set)
        io_handler(1, 0x71, 1,
                   nvr_read, NULL, NULL, nvr_write, NULL, NULL, nvr);
}

void
nvr_at_sec_handler(int set, uint16_t base, nvr_t *nvr)
{
    io_handler(set, base, 2,
               nvr_sec_read, NULL, NULL, nvr_sec_write, NULL, NULL, nvr);
}

void
nvr_read_addr_set(int set, nvr_t *nvr)
{
    local_t *local = (local_t *) nvr->data;

    local->read_addr = set;
}

void
nvr_wp_set(int set, int h, nvr_t *nvr)
{
    local_t *local = (local_t *) nvr->data;

    local->wp[h] = set;
}

void
nvr_via_wp_set(int set, int reg, nvr_t *nvr)
{
    local_t *local = (local_t *) nvr->data;

    if (reg == 0x0d)
        local->wp_0d = set;
    else
        local->wp_32 = set;
}

void
nvr_bank_set(int base, uint8_t bank, nvr_t *nvr)
{
    local_t *local = (local_t *) nvr->data;

    local->bank[base] = bank;
}

void
nvr_lock_set(int base, int size, int lock, nvr_t *nvr)
{
    local_t *local = (local_t *) nvr->data;

    for (int i = 0; i < size; i++)
        local->lock[base + i] = lock;
}

void
nvr_irq_set(int irq, nvr_t *nvr)
{
    nvr->irq = irq;
}

void
nvr_smi_enable(int enable, nvr_t *nvr)
{
    local_t *local = (local_t *) nvr->data;

    local->smi_enable = enable;

    if (!enable)
        local->smi_status = 0;
}

uint8_t
nvr_smi_status(nvr_t *nvr)
{
    const local_t *local = (local_t *) nvr->data;

    return local->smi_status;
}

void
nvr_smi_status_clear(nvr_t *nvr)
{
    local_t *local = (local_t *) nvr->data;

    local->smi_status = 0;
}

static void
nvr_at_reset(void *priv)
{
    nvr_t *nvr = (nvr_t *) priv;

    /* These bits are reset on reset. */
    nvr->regs[RTC_REGB] &= ~(REGB_PIE | REGB_AIE | REGB_UIE | REGB_SQWE);
    nvr->regs[RTC_REGC] &= ~(REGC_PF | REGC_AF | REGC_UF | REGC_IRQF);
}

static void *
nvr_at_init(const device_t *info)
{
    local_t *local;
    nvr_t   *nvr;

    /* Allocate an NVR for this machine. */
    nvr = (nvr_t *) malloc(sizeof(nvr_t));
    if (nvr == NULL)
        return (NULL);
    memset(nvr, 0x00, sizeof(nvr_t));

    local = (local_t *) malloc(sizeof(local_t));
    memset(local, 0x00, sizeof(local_t));
    nvr->data = local;

    /* This is machine specific. */
    nvr->size   = machines[machine].nvrmask + 1;
    local->lock = (uint8_t *) malloc(nvr->size);
    memset(local->lock, 0x00, nvr->size);
    local->def   = 0xff /*0x00*/;
    local->flags = 0x00;
    switch (info->local & 0x0f) {
        case 0: /* standard AT, no century register */
            if (info->local == 32) {
                local->flags |= FLAG_P6RP4_HACK;
                nvr->irq    = 8;
                local->cent = RTC_CENTURY_AT;
            } else {
                nvr->irq    = 8;
                local->cent = 0xff;
            }
            break;

        case 1: /* standard AT */
        case 5: /* AMI WinBIOS 1994 */
        case 6: /* AMI BIOS 1995 */
            if ((info->local & 0x1f) == 0x11) {
                local->flags |= FLAG_PIIX4;
                local->def = 0x00;
            } else {
                local->def = 0x00;
                if ((info->local & 0x1f) == 0x15)
                    local->flags |= FLAG_AMI_1994_HACK;
                else if ((info->local & 0x1f) == 0x16)
                    local->flags |= FLAG_AMI_1995_HACK;
                else
                    local->def = 0xff;
            }
            nvr->irq    = 8;
            local->cent = RTC_CENTURY_AT;
            break;

        case 2: /* PS/1 or PS/2 */
            nvr->irq    = 8;
            local->cent = RTC_CENTURY_PS;
            local->def  = 0x00;
            if (info->local & 0x10)
                local->flags |= FLAG_NO_NMI;
            break;

        case 3: /* Amstrad PC's */
            nvr->irq    = 1;
            local->cent = RTC_CENTURY_AT;
            local->def  = 0xff;
            if (info->local & 0x10)
                local->flags |= FLAG_NO_NMI;
            break;

        case 4: /* IBM AT */
            if (info->local & 0x10) {
                local->def = 0x00;
                local->flags |= FLAG_AMI_1992_HACK;
            } else if ((info->local == 36) || (info->local == 68)) {
                local->def = 0x00;
                if (info->local == 68)
                    local->flags |= FLAG_MARTIN_HACK;
            } else
                local->def = 0xff;
            nvr->irq    = 8;
            local->cent = RTC_CENTURY_AT;
            break;

        case 7: /* VIA VT82C586B */
            nvr->irq    = 8;
            local->cent = RTC_CENTURY_VIA;
            break;
        case 8: /* Epson Equity LT */
            nvr->irq    = -1;
            local->cent = RTC_CENTURY_ELT;
            break;

        default:
            break;
    }

    if (info->local & 0x20)
        local->def = 0x00;

    if (info->local & 0x40)
        local->flags |= FLAG_MULTI_BANK;

    local->read_addr = 1;

    /* Set up any local handlers here. */
    nvr->reset = nvr_reset;
    nvr->start = nvr_start;
    nvr->tick  = timer_tick;

    /* Initialize the generic NVR. */
    nvr_init(nvr);

    if (nvr->is_new && (local->flags & FLAG_MARTIN_HACK))
        nvr->regs[0x11] = nvr->regs[0x2f] = 0x02;

    if (nvr_at_inited == 0) {
        /* Start the timers. */
        timer_add(&local->update_timer, timer_update, nvr, 0);

        timer_add(&local->rtc_timer, timer_intr, nvr, 0);
        /* On power on, if the oscillator is disabled, it's reenabled. */
        if ((nvr->regs[RTC_REGA] & 0x70) == 0x00)
            nvr->regs[RTC_REGA] = (nvr->regs[RTC_REGA] & 0x8f) | 0x20;
        nvr_at_reset(nvr);
        timer_load_count(nvr);

        /* Set up the I/O handler for this device. */
        if (info->local == 8) {
            io_sethandler(0x11b4, 2,
                          nvr_read, NULL, NULL, nvr_write, NULL, NULL, nvr);
        } else {
            io_sethandler(0x0070, 2,
                          nvr_read, NULL, NULL, nvr_write, NULL, NULL, nvr);
        }
        if (((info->local & 0x1f) == 0x11) || ((info->local & 0x1f) == 0x17)) {
            io_sethandler(0x0072, 2,
                          nvr_read, NULL, NULL, nvr_write, NULL, NULL, nvr);
        }

        nvr_at_inited = 1;
    }

    /* This is a hack but it is required for the machine to boot properly, no idea why. */
    if (nvr->is_new && !strcmp(machine_get_internal_name(), "spitfire"))
        nvr->regs[0x33] = nvr->regs[0x34] = 0xff;

    return nvr;
}

static void
nvr_at_close(void *priv)
{
    nvr_t   *nvr   = (nvr_t *) priv;
    local_t *local = (local_t *) nvr->data;

    nvr_close();

    timer_disable(&local->rtc_timer);
    timer_disable(&local->update_timer);
    timer_disable(&nvr->onesec_time);

    if (nvr != NULL) {
        if (nvr->fn != NULL)
            free(nvr->fn);

        if (nvr->data != NULL)
            free(nvr->data);

        free(nvr);
    }

    if (nvr_at_inited == 1)
        nvr_at_inited = 0;
}

const device_t at_nvr_old_device = {
    .name          = "PC/AT NVRAM (No century)",
    .internal_name = "at_nvr_old",
    .flags         = DEVICE_ISA16,
    .local         = 0,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t at_nvr_device = {
    .name          = "PC/AT NVRAM",
    .internal_name = "at_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 1,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t at_mb_nvr_device = {
    .name          = "PC/AT NVRAM",
    .internal_name = "at_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 0x40 | 0x20 | 1,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t ps_nvr_device = {
    .name          = "PS/1 or PS/2 NVRAM",
    .internal_name = "ps_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 2,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t amstrad_nvr_device = {
    .name          = "Amstrad NVRAM",
    .internal_name = "amstrad_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 3,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t ibmat_nvr_device = {
    .name          = "IBM AT NVRAM",
    .internal_name = "ibmat_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 4,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t piix4_nvr_device = {
    .name          = "Intel PIIX4 PC/AT NVRAM",
    .internal_name = "piix4_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 0x10 | 1,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t ps_no_nmi_nvr_device = {
    .name          = "PS/1 or PS/2 NVRAM (No NMI)",
    .internal_name = "ps1_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 0x10 | 2,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t amstrad_no_nmi_nvr_device = {
    .name          = "Amstrad NVRAM (No NMI)",
    .internal_name = "amstrad_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 0x10 | 3,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t ami_1992_nvr_device = {
    .name          = "AMI Color 1992 PC/AT NVRAM",
    .internal_name = "ami_1992_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 0x10 | 4,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t ami_1994_nvr_device = {
    .name          = "AMI WinBIOS 1994 PC/AT NVRAM",
    .internal_name = "ami_1994_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 0x10 | 5,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t ami_1995_nvr_device = {
    .name          = "AMI WinBIOS 1995 PC/AT NVRAM",
    .internal_name = "ami_1995_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 0x10 | 6,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t via_nvr_device = {
    .name          = "VIA PC/AT NVRAM",
    .internal_name = "via_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 0x10 | 7,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t p6rp4_nvr_device = {
    .name          = "ASUS P/I-P6RP4 PC/AT NVRAM",
    .internal_name = "p6rp4_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 32,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t amstrad_megapc_nvr_device = {
    .name          = "Amstrad MegaPC NVRAM",
    .internal_name = "amstrad_megapc_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 36,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t martin_nvr_device = {
    .name          = "Zeos Martin NVRAM",
    .internal_name = "martin_nvr",
    .flags         = DEVICE_ISA16,
    .local         = 68,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};

const device_t elt_nvr_device = {
    .name          = "Epson Equity LT NVRAM",
    .internal_name = "elt_nvr",
    .flags         = DEVICE_ISA,
    .local         = 8,
    .init          = nvr_at_init,
    .close         = nvr_at_close,
    .reset         = nvr_at_reset,
    .available     = NULL,
    .speed_changed = nvr_at_speed_changed,
    .force_redraw  = NULL,
    .config        = NULL
};