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Handle low/high switches.

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This commit is contained in:
Thomas Harte 2023-11-21 11:25:53 -05:00
parent 931e6e7a56
commit acdf32e820
1 changed files with 16 additions and 5 deletions
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15
Machines/PCCompatible/PCCompatible.cpp
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@ -152,6 +152,7 @@ class i8255PortHandler : public Intel::i8255::PortHandler {
void set_value(int port, uint8_t value) {
switch(port) {
case 1:
high_switches_ = value & 0x08;
break;
}
printf("PPI: %02x to %d\n", value, port);
@ -159,21 +160,31 @@ class i8255PortHandler : public Intel::i8255::PortHandler {
uint8_t get_value(int port) {
switch(port) {
// TODO: returned value should depend on 'PBSW', a value written... somewhere?
case 2:
// Common:
//
// b7: 1 => memory parity error; 0 => none;
// b6: 1 => IO channel error; 0 => none;
// b5: timer 2 output; [TODO]
// b4: cassette data input; [TODO]
return
high_switches_ ?
// b3, b2: drive count; 00 = 1, 01 = 2, etc
// b1, b0: video mode (00 = ROM; 01 = CGA40; 10 = CGA80; 11 = MDA)
0b0000'0011
:
// b3, b2: RAM on motherboard (64 * bit pattern)
// b1: 1 => FPU present; 0 => absent;
// b0: 1 => floppy drive present; 0 => absent.
return 0b0000'1100;
0b0000'1100;
}
printf("PPI: from %d\n", port);
return 0;
};
private:
bool high_switches_ = false;
// Provisionally, possibly:
//
// port 0 = keyboard data output buffer;