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Actually update spec

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Lior Halphon 2021-04-12 22:43:23 +03:00
parent 9a1f962281
commit 9c1889f450
1 changed files with 16 additions and 15 deletions
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BESS.md
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@ -38,14 +38,14 @@ The length of the CORE block is 0xD0 bytes, but implementations are expected to
| Offset | Content |
|--------|---------------------------------------|
| 0x00 | Major BESS version as a 16-bit integer |
| 0x02 | Minor BESS version as a 16-bit integer |
| 0x00 | Major BESS version as a 16-bit integer |
| 0x02 | Minor BESS version as a 16-bit integer |
Both major and minor versions should be 1. Implementations are expected to reject incompatible majors, but still attempt to read newer minor versions.
| Offset | Content |
|--------|----------------------------------------|
| 0x04 | A four-character ASCII model identifier |
| 0x04 | A four-character ASCII model identifier |
BESS uses a four-character string to identify Game Boy models:
@ -58,23 +58,24 @@ For example; `'GD '` represents a DMG of an unspecified revision, `'S '` repr
| Offset | Content |
|--------|-------------------------------------------------------|
| 0x08 | The value of the PC register |
| 0x0A | The value of the AF register |
| 0x0C | The value of the BC register |
| 0x0E | The value of the DE register |
| 0x10 | The value of the HL register |
| 0x12 | The value of the SP register |
| 0x14 | The value of IME (0 or 1) |
| 0x15 | The value of the IE register |
| 0x16 | Execution state (0 = running; 1 = halted; 2 = stopped) |
| 0x17 | Reserved, must be 0 |
| 0x18 | The values of every memory-mapped register (128 bytes) |
| 0x08 | The value of the PC register |
| 0x0A | The value of the AF register |
| 0x0C | The value of the BC register |
| 0x0E | The value of the DE register |
| 0x10 | The value of the HL register |
| 0x12 | The value of the SP register |
| 0x14 | The value of IME (0 or 1) |
| 0x15 | The value of the IE register |
| 0x16 | Execution state (0 = running; 1 = halted; 2 = stopped) |
| 0x17 | Reserved, must be 0 |
| 0x18 | The values of every memory-mapped register (128 bytes) |
The values of memory-mapped registers should be written 'as-is' to memory as if the actual ROM wrote them, with the following exceptions and note:
* Unused registers have Don't-Care values which should be ignored
* Unused register bits have Don't-Care values which should be ignored
* The value of KEY0 (FF4C) must be valid as it determines CGB mode
* The value of KEY0 (FF4C) must be valid as it determines DMG mode when the model is CGB or newer
* Sprite priority is derived from KEY0 (FF4C) instead of OPRI (FF6C) because OPRI can be modified after booting, but only the value of OPRI during boot ROM execution takes effect
* If a register doesn't exist on the emulated model (For example, KEY0 (FF4C) on a DMG), its value should be ignored.
* BANK (FF50) should be 0 if the boot ROM is still mapped, and 1 otherwise, and must be valid.
* Implementations should not start a serial transfer when writing the value of SB
* Similarly, no value of NRx4 should trigger a sound pulse on save state load