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apple2 fakeDrive: PROM bytes on read, JMP on exec

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This commit is contained in:
Micah Cowan 2022-01-27 19:42:32 -08:00
parent 8e3f929098
commit c58d999ee4
1 changed files with 41 additions and 11 deletions
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52
src/machine/apple2.ts
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@ -66,17 +66,47 @@ export class AppleII extends BasicScanlineMachine implements AcceptsBIOS {
// fake disk drive that loads program into RAM
fakeDrive : SlotDevice = {
readROM: (a) => {
switch (a) {
// JMP VM_BASE
case 0: {
// load program into RAM
if (this.rom)
this.ram.set(this.rom.slice(HDR_SIZE), PGM_BASE);
return 0x4c;
}
case 1: return VM_BASE&0xff;
case 2: return (VM_BASE>>8)&0xff;
default: return 0;
var pc = this.cpu.getPC();
if (pc >= 0xC600 && pc < 0xC700) {
// We're reading code to EXECUTE.
// Load the built program directly into memory, and "read"
// a JMP directly to it.
//console.log(`fakeDrive (EXEC): ${a.toString(16)}`);
switch (a) {
// JMP VM_BASE
case 0:
// SHOULD load program into RAM here, but have to do it
// below instead.
return 0;
case 1: return VM_BASE&0xff;
case 2: return (VM_BASE>>8)&0xff;
default: return 0;
}
}
else {
// We're reading code, but not executing it.
// This is probably the Monitor routine to identify whether
// this slot is a Disk ][ drive, so... give it what it wants.
//console.log(`fakeDrive (NOEX): ${a.toString(16)}`);
switch (a) {
case 0:
// Actually, if we get here, we probably ARE being
// executed. For some reason, the instruction at $C600
// gets read for execution, BEFORE the PC gets set to
// the correct location. So we handle loading the program
// into RAM and returning the JMP here, instead of above
// where it would otherwise belong.
if (this.rom) {
console.log(`Loading program into Apple ][ RAM at \$${PGM_BASE.toString(16)}`);
this.ram.set(this.rom.slice(HDR_SIZE), PGM_BASE);
}
return 0x4c; // JMP
case 1: return 0x20;
case 3: return 0x00;
case 5: return 0x03;
case 7: return 0x3c;
default: return 0;
}
}
},
readConst: (a) => {