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Update Tandy emulation vs memsizekb setting, add FIXME reminders, etc

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This commit is contained in:
Jonathan Campbell
2021-03-22 23:22:52 -07:00
parent 6f66922f8c
commit 88a99c1226
2 changed files with 19 additions and 15 deletions
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9
src/dos/dos_memory.cpp
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@@ -559,11 +559,10 @@ void DOS_SetupMemory(void) {
if (machine==MCH_TANDY) {
if (seg_limit < ((384*1024)/16))
E_Exit("Tandy requires at least 384K");
/* memory up to 608k available, the rest (to 640k) is used by
the tandy graphics system's variable mapping of 0xb800 */
/*
mcb.SetSize(0x9BFF - DOS_MEM_START - mcb_sizes);
*/ mcb.SetSize(/*0x9BFF*/(seg_limit-0x801) - DOS_MEM_START - mcb_sizes);
/* map memory as normal, the BIOS initialization is the code responsible
* for subtracting 32KB from top of system memory for video memory. */
mcb.SetSize(/*normally 0x97FF*/(seg_limit-1) - DOS_MEM_START - mcb_sizes);
} else if (machine==MCH_PCJR) {
DOS_MCB mcb_devicedummy((uint16_t)0x2000);

25
src/ints/bios.cpp
View File

@@ -9286,16 +9286,6 @@ public:
if (t_conv > 640) t_conv = 640;
}
#if 0 /* NTS: This breaks Tandy games that write to system RAM addresses to draw on video RAM i.e.
not at B800:xxxx but at (TOP_OF_MEMORY minus 32KB). What is the correct behavior
here? */
if (IS_TANDY_ARCH) {
/* reduce reported memory size for the Tandy (32k graphics memory
at the end of the conventional 640k) */
if (machine==MCH_TANDY && t_conv > 624) t_conv = 624;
}
#endif
/* allow user to further limit the available memory below 1MB */
if (dos_conventional_limit != 0 && t_conv > dos_conventional_limit)
t_conv = dos_conventional_limit;
@@ -9308,11 +9298,26 @@ public:
if (isa_memory_hole_512kb && t_conv > 512) t_conv = 512;
if (machine == MCH_TANDY) {
if (t_conv < 384)
E_Exit("Tandy requires at least 384KB of RAM");
/* The shared video/system memory design, and the placement of video RAM at top
* of conventional memory, means that if conventional memory is less than 640KB
* and not a multiple of 32KB, things can break. */
if ((t_conv % 32) != 0)
LOG(LOG_MISC,LOG_WARN)("Warning: Conventional memory size %uKB in Tandy mode is not a multiple of 32KB, games may not display graphics correctly",t_conv);
/* take 32KB off the top for video RAM. */
if (t_conv > 640) t_conv = 640;
if (ulimit > 640) ulimit = 640;
t_conv -= 32;
ulimit -= 32;
/* FIXME: INT 10h emulation currently points video RAM at 9800:0000 regardless of
* the amount of conventional memory, which happens to work as long as the
* game or application only writes to segment B800:0000. The system RAM
* backing the video ram is invisible because it's beyond the available
* conventional memory reported to the guest and therefore not mapped. */
}
else if (machine == MCH_PCJR) {
/* PCjr also shares video/system memory, but the video memory can only exist