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Merge pull request #1494 from TomHarte/MoreAT

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AT: adjust reported RAM refresh timing.
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Thomas Harte 2025-03-16 15:54:27 -04:00 committed by GitHub
commit 15da707324
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GPG Key ID: B5690EEEBB952194
2 changed files with 16 additions and 23 deletions
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18
Machines/PCCompatible/KeyboardController.hpp
View File

@ -118,6 +118,7 @@ public:
KeyboardController(PICs<model> &pics, Speaker &speaker) : pics_(pics), speaker_(speaker) {}
void run_for(const Cycles cycles) {
instruction_count_ += cycles.as<int>();
if(!write_delay_) return;
write_delay_ -= cycles.as<int>();
if(write_delay_ <= 0) {
@ -181,15 +182,12 @@ public:
return input_;
case 0x0061:
// In a real machine bit 4 toggles as a function of memory refresh; it is often
// used by BIOSes to check that refresh is happening, with no greater inspection
// than that it is toggling. So toggle on read.
//
// TODO: is this really from the keyboard controller?
refresh_toggle_ ^= 0x10;
// log_.info().append("AT keyboard: %02x from %04x", refresh_toggle_, port);
return refresh_toggle_;
// In a real machine bit 4 toggles as a function of memory refresh and some BIOSes
// (including IBM's) do a polled loop to test its speed. So that effectively compares
// PIT counts against CPU cycle counts. Since this emulator does nothing whatsoever
// to attempt realistic CPU timing, the ratio here is just one I found that passed
// BIOS inspection. I may have overfitted to IBM's. This counts as an ugliness.
return ((instruction_count_ * 2) / 25) & 0x10;
case 0x0064: {
// Status:
@ -301,7 +299,7 @@ private:
Speaker &speaker_;
CPUControl<model> *cpu_control_ = nullptr;
uint8_t refresh_toggle_ = 0;
int instruction_count_ = 0;
bool has_input_ = false;
uint8_t input_;

21
Machines/PCCompatible/PCCompatible.cpp
View File

@ -619,13 +619,16 @@ public:
throw ROMMachine::Error::MissingROMs;
}
const auto install_bios = [&](const std::vector<uint8_t> &source) {
context_.memory.install(0x10'0000 - source.size(), source.data(), source.size());
};
switch(pc_model) {
default: {
const auto &bios_contents = roms.find(bios_XT)->second;
context_.memory.install(0x10'0000 - bios_contents.size(), bios_contents.data(), bios_contents.size());
install_bios(roms.find(bios_XT)->second);
// If found, install GlaTICK at 0xd'0000.
auto tick_contents = roms.find(tick_XT);
const auto tick_contents = roms.find(tick_XT);
if(tick_contents != roms.end()) {
context_.memory.install(0xd'0000, tick_contents->second.data(), tick_contents->second.size());
}
@ -642,22 +645,14 @@ public:
bios[c] = (c & 1) ? bios_odd->second[c >> 1] : bios_even->second[c >> 1];
}
context_.memory.install(
0x10'0000 - bios.size(),
bios.data(),
bios.size()
);
install_bios(bios);
return;
}
for(const auto name: {bios_AT, bios_AT_Phoenix}) {
const auto bios_contents = roms.find(name);
if(bios_contents != roms.end()) {
context_.memory.install(
0x10'0000 - bios_contents->second.size(),
bios_contents->second.data(),
bios_contents->second.size()
);
install_bios(bios_contents->second);
return;
}
}