53c9x changes of the night (August 11th, 2025)

1. Add the original AMD 53c974 (AMD bios only and revision 0x00 compared to the A revision which is 0x10 in the PCI regs) as well as correcting the SCSI bus reset when prompted (ESP CMD 0x03), the latter fixes DawiControl 53c974 drivers on win9x.
2. Check if DMA length is not 0 for DMA transfers.
3. More logs for possible problem diagnostics.

src/include/86box/scsi_pcscsi.h

@@ -26,6 +26,7 @@
 #define SCSI_PCSCSI_H
 
 extern const device_t am53c974_pci_device;
+extern const device_t am53c974a_pci_device;
 extern const device_t dc390_pci_device;
 extern const device_t ncr53c90a_mca_device;
 

src/scsi/scsi.c

@@ -84,6 +84,7 @@ static SCSI_CARD scsi_cards[] = {
     { &buslogic_445c_device,     },
     /* PCI */
     { &am53c974_pci_device,      },
+    { &am53c974a_pci_device,     },
     { &buslogic_958d_pci_device, },
     { &ncr53c810_pci_device,     },
     { &ncr53c815_pci_device,     },

src/scsi/scsi_pcscsi.c

@@ -141,6 +141,7 @@ enum ESPASCMode {
 
 #define CFG1_RESREPT     0x40
 
+#define TCHI_ESP100A     0x01
 #define TCHI_FAS100A     0x04
 #define TCHI_AM53C974    0x12
 
@@ -666,6 +667,7 @@ esp_hard_reset(esp_t *dev)
     dev->tchi_written    = 0;
     dev->asc_mode = ESP_ASC_MODE_DIS;
     dev->rregs[ESP_CFG1] = dev->mca ? dev->HostID : 7;
+    dev->sbac = 1 << 19;
 
     esp_log("ESP Reset\n");
 
@@ -716,7 +718,7 @@ esp_do_dma(esp_t *dev)
 
     len = esp_get_tc(dev);
 
-    esp_log("ESP SCSI Actual DMA len=%d, cfg3=%02x.\n", len, dev->rregs[ESP_CFG3]);
+    esp_log("ESP SCSI Actual DMA len=%d, cfg3=%02x, phase=%x.\n", len, dev->rregs[ESP_CFG3], esp_get_phase(dev));
 
     switch (esp_get_phase(dev)) {
         case STAT_MO:
@@ -1316,6 +1318,7 @@ handle_s_without_atn(void *priv)
     if (esp_select(dev) < 0)
         return;
 
+    esp_log("Selection without ATN.\n");
     esp_set_phase(dev, STAT_CD);
     dev->cmdfifo_cdb_offset = 0;
 
@@ -1333,6 +1336,7 @@ handle_satn(void *priv)
     if (esp_select(dev) < 0)
         return;
 
+    esp_log("Selection with ATN.\n");
     esp_set_phase(dev, STAT_MO);
 
     if (dev->dma)
@@ -1434,12 +1438,17 @@ esp_reg_read(esp_t *dev, uint32_t saddr)
             esp_log("Read Interrupt=%02x (old).\n", ret);
             break;
         case ESP_TCHI: /* Return the unique id if the value has never been written */
-            if (!dev->mca && !dev->tchi_written)
+            if (!dev->tchi_written) {
-                ret = TCHI_AM53C974;
+                if (dev->mca)
+                    ret = TCHI_ESP100A;
                 else
-                ret = dev->rregs[ESP_TCHI];
+                    ret = TCHI_AM53C974;
 
+                esp_log("ChipID=%02x.\n", ret);
+            } else {
+                ret = dev->rregs[ESP_TCHI];
                 esp_log("Read TCHI Register=%02x.\n", ret);
+            }
             break;
         case ESP_RFLAGS:
             ret = fifo8_num_used(&dev->fifo);
@@ -1525,6 +1534,12 @@ esp_reg_write(esp_t *dev, uint32_t saddr, uint32_t val)
                     break;
                 case CMD_BUSRESET:
                     esp_log("ESP Bus Reset val=%02x.\n", (dev->rregs[ESP_CFG1] & CFG1_RESREPT));
+                    if (dev->mca) {
+                        esp_lower_irq(dev);
+                        esp_hard_reset(dev);
+                    } else
+                        esp_pci_soft_reset(dev);
+
                     for (uint8_t i = 0; i < 16; i++) {
                         scsi_device_reset(&scsi_devices[dev->bus][i]);
                     }
@@ -1635,6 +1650,7 @@ esp_pci_dma_memory_rw(esp_t *dev, uint8_t *buf, uint32_t len, int dir)
     if (dev->dma_regs[DMA_WBC] < len)
         len = dev->dma_regs[DMA_WBC];
 
+    esp_log("DMA Length=%d.\n", len);
     if (dev->dma_regs[DMA_CMD] & DMA_CMD_MDL) {
         if (len) {
             dma_bm_read(dev->dma_regs[DMA_WMAC], (uint8_t *)&DMAPtr, 4, 4);
@@ -1681,6 +1697,7 @@ esp_pci_dma_memory_rw(esp_t *dev, uint8_t *buf, uint32_t len, int dir)
             }
         }
     } else {
+        if (len) {
             addr = dev->dma_regs[DMA_WAC];
 
             if (expected_dir)
@@ -1692,6 +1709,7 @@ esp_pci_dma_memory_rw(esp_t *dev, uint8_t *buf, uint32_t len, int dir)
             dev->dma_regs[DMA_WBC] -= len;
             dev->dma_regs[DMA_WAC] += len;
         }
+    }
 
     esp_log("Finished count=%d.\n", dev->dma_regs[DMA_WBC]);
     if (dev->dma_regs[DMA_WBC] == 0) {
@@ -2184,7 +2202,7 @@ esp_pci_read(UNUSED(int func), int addr, void *priv)
         case 0x07:
             return esp_pci_regs[0x07] | 0x02;
         case 0x08:
-            return 0x10; /*Revision ID*/
+            return (dev->local == 1) ? 0 : 0x10; /*Revision ID*/
         case 0x09:
             return 0; /*Programming interface*/
         case 0x0A:
@@ -2363,7 +2381,7 @@ esp_pci_reset(void *priv)
 
     memcpy(dev, &reset_state, sizeof(esp_t));
 
-    dev->sbac = 1 << 19;
+    esp_pci_soft_reset(dev);
 }
 
 static void *
@@ -2650,6 +2668,44 @@ static const device_config_t bios_enable_config[] = {
   // clang-format on
 };
 
+static const device_config_t am53c974_bios_enable_config[] = {
+  // clang-format off
+    {
+        .name           = "bios_rev",
+        .description    = "BIOS Revision",
+        .type           = CONFIG_BIOS,
+        .default_string = "v3_01_amd",
+        .default_int    = 0,
+        .file_filter    = NULL,
+        .spinner        = { 0 },
+        .bios           = {
+            {
+                .name          = "Version 3.01 (AMD)",
+                .internal_name = "v3_01_amd",
+                .bios_type     = BIOS_NORMAL,
+                .files_no      = 1,
+                .local         = 0,
+                .size          = 16384,
+                .files         = { AM53C974_3_01_AMD_ROM, "" }
+            },
+            { .files_no = 0 }
+        },
+    },
+    {
+        .name           = "bios",
+        .description    = "Enable BIOS",
+        .type           = CONFIG_BINARY,
+        .default_string = NULL,
+        .default_int    = 0,
+        .file_filter    = NULL,
+        .spinner        = { 0 },
+        .selection      = { { 0 } },
+        .bios           = { { 0 } }
+    },
+    { .name = "", .description = "", .type = CONFIG_END }
+  // clang-format on
+};
+
 static const device_config_t am53c974a_bios_enable_config[] = {
   // clang-format off
     {
@@ -2739,7 +2795,7 @@ const device_t dc390_pci_device = {
 };
 
 const device_t am53c974_pci_device = {
-    .name          = "AMD 53c974A PCI",
+    .name          = "AMD 53c974 PCI",
     .internal_name = "am53c974",
     .flags         = DEVICE_PCI,
     .local         = 1,
@@ -2749,6 +2805,20 @@ const device_t am53c974_pci_device = {
     .available     = NULL,
     .speed_changed = NULL,
     .force_redraw  = NULL,
+    .config        = am53c974_bios_enable_config
+};
+
+const device_t am53c974a_pci_device = {
+    .name          = "AMD 53c974A PCI",
+    .internal_name = "am53c974a",
+    .flags         = DEVICE_PCI,
+    .local         = 2,
+    .init          = dc390_init,
+    .close         = esp_close,
+    .reset         = esp_pci_reset,
+    .available     = NULL,
+    .speed_changed = NULL,
+    .force_redraw  = NULL,
     .config        = am53c974a_bios_enable_config
 };