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Decode PIT mode writes.

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This commit is contained in:
Thomas Harte 2023-11-19 14:59:52 -05:00
parent 2b69081fff
commit af885ccf08
1 changed files with 46 additions and 3 deletions
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49
Machines/PCCompatible/PCCompatible.cpp
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@ -20,6 +20,7 @@
namespace PCCompatible { namespace PCCompatible {
template <bool is_8254>
class PIT { class PIT {
public: public:
template <int channel> uint8_t read() { template <int channel> uint8_t read() {
@ -29,16 +30,58 @@ class PIT {
template <int channel> void write([[maybe_unused]] uint8_t value) { template <int channel> void write([[maybe_unused]] uint8_t value) {
} }
void set_mode([[maybe_unused]] uint8_t value) { void set_mode(uint8_t value) {
const int channel = (value >> 6) & 3; const int channel_id = (value >> 6) & 3;
if(channel == 3) { if(channel_id == 3) {
read_back_ = is_8254;
return; return;
} }
Channel &channel = channels_[channel_id];
channel.is_bcd = value & 1;
switch((value >> 1) & 3) {
default: channel.latch_value(); break;
case 1: channel.latch_mode = LatchMode::LowOnly; break;
case 2: channel.latch_mode = LatchMode::HighOnly; break;
case 3: channel.latch_mode = LatchMode::LowHigh; break;
}
const auto operating_mode = (value >> 3) & 7;
switch(operating_mode) {
default: channel.mode = OperatingMode(operating_mode); break;
case 6: channel.mode = OperatingMode::RateGenerator; break;
case 7: channel.mode = OperatingMode::SquareWaveGenerator; break;
}
} }
private: private:
// Supported only on 8254s.
bool read_back_ = false;
enum class LatchMode { enum class LatchMode {
LowOnly,
HighOnly,
LowHigh,
}; };
enum class OperatingMode {
InterruptOnTerminalCount = 0,
HardwareRetriggerableOneShot = 1,
RateGenerator = 2,
SquareWaveGenerator = 3,
SoftwareTriggeredStrobe = 4,
HardwareTriggeredStrobe = 5,
};
struct Channel {
LatchMode latch_mode = LatchMode::LowHigh;
OperatingMode mode = OperatingMode::InterruptOnTerminalCount;
bool is_bcd = false;
void latch_value() {}
} channels_[3];
}; };
struct Registers { struct Registers {