Upgrade to NES2.0 header

build.js

@@ -27,6 +27,7 @@ if (args.includes('-h')) {
 -k  Famicom Keyboard support
 -w  force WASM compiler
 -c  force PNG to CHR conversion
+-i  use iNES header instead of NES2.0
 -o  override autodetect mmc1 header with cnrom
 -t  run tests (requires cargo)
 -h  you are here
@@ -79,9 +80,15 @@ if (args.includes('-k')) {
 
 if (args.includes('-s')) {
     compileFlags.push('-D', 'SAVE_HIGHSCORES=0');
+    compileFlags.push('-D', 'HAS_SRAM=0');
     console.log('highscore saving disabled');
 }
 
+if (args.includes('-i')) {
+    compileFlags.push('-D', 'INES_OVERRIDE=1');
+    console.log('iNES header override');
+}
+
 if (args.includes('-o')) {
     compileFlags.push('-D', 'CNROM_OVERRIDE=1');
     console.log('cnrom override for autodetect');

src/constants.asm

@@ -6,6 +6,10 @@ INES_MAPPER := 1000 ; 0 (NROM), 1 (MMC1), 3 (CNROM), 4 (MMC3), 5 (MMC5), and 100
 SAVE_HIGHSCORES := 1
 .endif
 
+.ifndef HAS_SRAM
+HAS_SRAM := 1
+.endif
+
 .ifndef AUTO_WIN
 ; faster aeppoz + press select to end game
 AUTO_WIN := 0
@@ -15,6 +19,10 @@ AUTO_WIN := 0
 KEYBOARD := 0
 .endif
 
+.ifndef INES_OVERRIDE
+INES_OVERRIDE := 0
+.endif
+
 .ifndef CNROM_OVERRIDE
 CNROM_OVERRIDE := 0
 .endif

src/header.asm

@@ -1,16 +1,20 @@
 ;
-; iNES header
+; NES2.0 header
+; https://www.nesdev.org/wiki/NES_2.0
 ;
 
-; This iNES header is from Brad Smith (rainwarrior)
+; iNES header adapted from Brad Smith (rainwarrior)
 ; https://github.com/bbbradsmith/NES-ca65-example
 
 .segment "HEADER"
 
 .include "constants.asm" ; for INES_HEADER
 
 INES_MIRROR = 0 ; 0 = horizontal mirroring, 1 = vertical mirroring (ignored in MMC1)
-INES_SRAM   = 1 ; 1 = battery backed SRAM at $6000-7FFF
+INES_SRAM = HAS_SRAM ; 1 = battery backed SRAM at $6000-7FFF
+NES2_SRAM_SHIFT = HAS_SRAM * 7 ; if SRAM present, set shift to 7 for (64 << 7) = 8KiB size
+NES2_REGION = 2 ; 0 = NTSC, 1 = PAL, 2 = multi-region, 3 = UA6538 ("Dendy")
+NES2_INPUT = 0 ; 0 = unspecified, 1 = standard NES/FC controllers, $23 = Family BASIC Keyboard
 
 ; Override INES_MAPPER for mode 1000 (auto detect)
 .if INES_MAPPER = 1000
@@ -20,12 +24,31 @@ INES_SRAM   = 1 ; 1 = battery backed SRAM at $6000-7FFF
     _INES_MAPPER = 1 ; MMC1 for Emulator/Flashcart
     .endif
 .else
-_INES_MAPPER = INES_MAPPER ; use actual INES_MAPPER otherwise
+    _INES_MAPPER = INES_MAPPER ; use actual INES_MAPPER otherwise
 .endif
 
+; Pick the appropriate NES2_SUBMAPPER
+.if _INES_MAPPER = 1
+    NES2_SUBMAPPER = 5 ; MMC1 fixed PRG
+.elseif _INES_MAPPER = 3
+    NES2_SUBMAPPER = 2 ; CNROM bus conflicts
+.else
+    NES2_SUBMAPPER = 0 ; otherwise don't specify submapper
+.endif
+
+; Construct header
 .byte 'N', 'E', 'S', $1A ; ID
 .byte $02 ; 16k PRG chunk count
 .byte $02 ; 8k CHR chunk count
 .byte INES_MIRROR | (INES_SRAM << 1) | ((_INES_MAPPER & $f) << 4)
-.byte (_INES_MAPPER & %11110000)
-.byte $0, $0, $0, $0, $0, $0, $0, $0 ; padding
+
+.if INES_OVERRIDE = 0
+    .byte (_INES_MAPPER & %11110000) | %00001000 ; NES2.0 header identifier
+    .byte ((NES2_SUBMAPPER & $f) << 4) | ((_INES_MAPPER & $f00) >> 8) ; submapper/mapper MSB
+    .byte $0, (NES2_SRAM_SHIFT << 4) ; PRG MSB, SRAM shift count
+    .byte $0, NES2_REGION, $0, $0, NES2_INPUT ; misc. fields, region, input device
+.else
+    .byte (_INES_MAPPER & %11110000)
+    .byte $0, $0, $0, $0, $0, $0, $0, $0 ; padding
+.endif
+