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This commit is contained in:
Akamaki
2025-02-15 19:49:03 +09:00
parent 59c3bb794f
commit 6c5e8897de
2 changed files with 9 additions and 10 deletions
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13
src/video/vid_svga.c
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@@ -502,20 +502,19 @@ svga_in(uint16_t addr, void *priv)
ret = svga->attrregs[svga->attraddr];
break;
case 0x3c2:
if (svga->cable_connected)
{
if (svga->cable_connected) {
if ((svga->vgapal[0].r + svga->vgapal[0].g + svga->vgapal[0].b) >= 0x4e)
ret = 0;
else
ret = 0x10;
}
else
{
/* Monitor is not connected to the planar VGA if the PS/55 Display Adapter is installed. */
} else {
/*
The IBM PS/55 Display Adapter has own Monitor Type Detection bit in the different I/O port (I/O 3E0h, 3E1h).
When the monitor cable is connected to the Display Adapter, this port returns the value as 'no cable connection'.
When the monitor cable is connected to the Display Adapter, the port 3C2h returns the value as 'no cable connection'.
The POST of PS/55 has an extra code that tries detecting the monitor on the planar VGA.
If it fails, then the POST reads the NVRAM set by the reference diskette, and updates the BIOS Data Area (Mem 487h, 489h).
If it fails, then the POST reads the NVRAM set by the reference diskette, and writes the BIOS Data Area (Mem 487h, 489h).
MONCHK.EXE in the reference diskette uses both I/O ports to determine the monitor type, and writes the BDA.
*/
if (svga->vgapal[0].r >= 10 || svga->vgapal[0].g >= 10 || svga->vgapal[0].b >= 10)
ret = 0;