From 9c1889f4500b29daeb07631649a4f34308e78088 Mon Sep 17 00:00:00 2001 From: Lior Halphon Date: Mon, 12 Apr 2021 22:43:23 +0300 Subject: [PATCH] Actually update spec --- BESS.md | 31 ++++++++++++++++--------------- 1 file changed, 16 insertions(+), 15 deletions(-) diff --git a/BESS.md b/BESS.md index ab4f3ea6..d31e1744 100644 --- a/BESS.md +++ b/BESS.md @@ -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