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Fix issue #187 were bank writing was not working correctly 

Before, `mmu.ts` would deactivate writing to the language card if
`prewrite` was reset.  However, it is totally possible to reset
`prewrite` and leave writing enabled, as shown my Sather in
_Understanding the Apple IIe_, table 5.5, p. 5-24.  For example:

```assembly_x86
    sta  $c08a  ; WRITE DISABLE; READ DISABLE
    lda  $c08b  ; PRE-WRITE set
    lda  $c08b  ; WRITE enabled
    sta  $c08a  ; PRE-WRITE reset; WRITE still enabled!
    lda  $c08b  ; PRE-WRITE set; WRITE still enabled!
```

would not work correctly because the last line would clear `_writebsr`
before setting `_prewrite`, which is incorrect.

Now, `_writebsr` is only set when `_prewrite` is set and thus only
cleared when `writeSwitch` is false.  This matches Table 5.5.
This commit is contained in:
Ian Flanigan 2023-06-25 12:57:03 +02:00
parent dd432b505b
commit d6d67b2a44
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2 changed files with 93 additions and 1 deletions
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4
js/mmu.ts
View File

@ -684,7 +684,9 @@ export default class MMU implements Memory, Restorable<MMUState> {
if (writeSwitch) { // 0xC081, 0xC083
if (readMode) {
this._writebsr = this._prewrite;
if (this._prewrite) {
this._writebsr = true;
}
}
this._prewrite = readMode;

90
test/js/mmu.test.ts Normal file
View File

@ -0,0 +1,90 @@
import Apple2IO from 'js/apple2io';
import MMU from '../../js/mmu';
import CPU6502 from 'js/cpu6502';
import { HiresPage, LoresPage, VideoModes, VideoPage } from 'js/videomodes';
import Apple2eROM from '../../js/roms/system/apple2e';
import { MemoryPages } from 'js/types';
function newFakeMemoryPages() {
return {} as unknown as MemoryPages;
}
function newFakeVideoPage(): VideoPage {
const bank0Pages = newFakeMemoryPages();
const bank1Pages = newFakeMemoryPages();
return {
bank0() {
return bank0Pages;
},
bank1() {
return bank1Pages;
},
} as unknown as VideoPage;
}
function newFakeLoresPage(): LoresPage {
return newFakeVideoPage() as unknown as LoresPage;
}
function newFakeHiresPage(): HiresPage {
return newFakeVideoPage() as unknown as HiresPage;
}
describe('MMU', () => {
const fakeVideoModes = {} as unknown as VideoModes;
const fakeCPU = {} as unknown as CPU6502;
const fakeLoResPage1 = newFakeLoresPage();
const fakeLoResPage2 = newFakeLoresPage();
const fakeHiResPage1 = newFakeHiresPage();
const fakeHiResPage2 = newFakeHiresPage();
const fakeApple2IO = {} as unknown as Apple2IO;
it('is constructable', () => {
const mmu = new MMU(fakeCPU, fakeVideoModes, fakeLoResPage1, fakeLoResPage2,
fakeHiResPage1, fakeHiResPage2, fakeApple2IO, new Apple2eROM());
expect(mmu).not.toBeNull();
});
it('requires prewrite to write to bank1', () => {
const mmu = new MMU(fakeCPU, fakeVideoModes, fakeLoResPage1, fakeLoResPage2,
fakeHiResPage1, fakeHiResPage2, fakeApple2IO, new Apple2eROM());
// From https://github.com/whscullin/apple2js/issues/187
// Action descriptions from Sather, Table 5.5, p. 5-24, UtAIIe:
mmu._access(0x8b); // WRTCOUNT = WRTCOUNT + 1, READ ENABLE
mmu._access(0x8b); // WRTCOUNT = WRTCOUNT + 1, READ ENABLE (write enabled)
mmu._access(0x89, 0x00); // WRTCOUNT = 0, READ DISABLE (write still enabled)
mmu._access(0x89); // WRTCOUNT = WRITCOUNT + 1, READ DISABLE (write still enabled)
mmu.write(0xd0, 0x00, 0xa1);
mmu._access(0x8b); // WRTCOUNT = WRTCOUNT + 1, READ ENABLE (write still enabled)
expect(mmu.read(0xd0, 0x00)).toBe(0xa1);
});
it('prewrite is reset on write access before write', () => {
const mmu = new MMU(fakeCPU, fakeVideoModes, fakeLoResPage1, fakeLoResPage2,
fakeHiResPage1, fakeHiResPage2, fakeApple2IO, new Apple2eROM());
// Action descriptions from Sather, Table 5.5, p. 5-24, UtAIIe:
mmu._access(0x89, 0x00); // WRTCOUNT = 0, READ DISABLE
mmu._access(0x8b); // WRTCOUNT = WRTCOUNT + 1, READ ENABLE (write not enabled yet)
mmu._access(0x8b, 0x00); // WRTCOUNT = 0, READ ENABLE (write still not enabled)
const oldValue = mmu.read(0xd0, 0x00);
mmu.write(0xd0, 0x00, 0xa1); // writes to the void
expect(mmu.read(0xd0, 0x00)).toBe(oldValue); // reads old value
});
it('write stays active with overzealous switching', () => {
const mmu = new MMU(fakeCPU, fakeVideoModes, fakeLoResPage1, fakeLoResPage2,
fakeHiResPage1, fakeHiResPage2, fakeApple2IO, new Apple2eROM());
// Action descriptions from Sather, Table 5.5, p. 5-24, UtAIIe:
mmu._access(0x8b); // WRTCOUNT = WRTCOUNT + 1, READ ENABLE
mmu._access(0x8b); // WRTCOUNT = WRTCOUNT + 1, READ ENABLE (write enabled)
mmu._access(0x8b); // WRTCOUNT = WRTCOUNT + 1, READ ENABLE (write enabled)
mmu._access(0x8b); // WRTCOUNT = WRTCOUNT + 1, READ ENABLE (write enabled)
mmu.write(0xd0, 0x00, 0xa1);
mmu._access(0x8b); // WRTCOUNT = WRTCOUNT + 1, READ ENABLE (write still enabled)
expect(mmu.read(0xd0, 0x00)).toBe(0xa1);
});
});