NES GTROM cannot use CHR-ROM

Mesen will detect MMC1 if CHR-ROM is present, since there is a conflict
for mapper 111 with a Chinese fan translation of Ninja Gaiden.

Author: mysterymath

mos-platform/nes-gtrom/common.ld

@@ -2,15 +2,10 @@
 
 INCLUDE nes.ld
 
-ASSERT(__prg_rom_size <= 512,
-       "GTROM only supports up to 512 KiB of PRG.")
+ASSERT(__prg_rom_size <= 512, "GTROM only supports up to 512 KiB of PRG.")
 
-ASSERT(__chr_rom_size <= 16,
-       "GTROM only supports up to 16 KiB of CHR-ROM.")
 ASSERT(__chr_ram_size + __chr_nvram_size <= 16,
        "GTROM only supports up to 16 KiB of CHR-(NV)RAM.")
 
-ASSERT(__prg_ram_size == 0,
-       "GTROM does not support PRG-RAM")
-ASSERT(__prg_nvram_size == 0,
-       "GTROM does not support PRG-NVRAM")
+ASSERT(__prg_ram_size == 0, "GTROM does not support PRG-RAM")
+ASSERT(__prg_nvram_size == 0, "GTROM does not support PRG-NVRAM")

mos-platform/nes-gtrom/ines.s

@@ -4,8 +4,8 @@
 __mapper = 111
 
 ; GTROM boards come with CHR-RAM by default.
-; Setting this to 0 gives CHR-ROM.
 .weak __chr_ram_size
 __chr_ram_size = 16
-.weak __chr_rom_size
+
+.globl __chr_rom_size
 __chr_rom_size = 0

test/nes-gtrom/CMakeLists.txt

@@ -5,7 +5,6 @@ project(test-nes-gtrom LANGUAGES C)
 include(../test.cmake)
 
 add_nes_test(chr-ram)
-add_nes_test(chr-rom)
 add_nes_test(chr-swap-split)
 add_nes_test(minimal)
 add_nes_test(prg-rom-512)

test/nes-gtrom/chr-ram.c

@@ -3,9 +3,6 @@
 #include <peekpoke.h>
 #include <stdlib.h>
 
-MAPPER_CHR_ROM_KB(0);
-MAPPER_CHR_RAM_KB(16);
-
 void poke_ppu(unsigned addr, char val) {
   PPU.vram.address = addr >> 8;
   PPU.vram.address = (char)addr;

test/nes-gtrom/chr-rom.c

@@ -3,14 +3,6 @@
 #include <peekpoke.h>
 #include <stdlib.h>
 
-MAPPER_CHR_ROM_KB(16);
-MAPPER_CHR_RAM_KB(0);
-
-__attribute__((used, section(".chr_rom_0")))
-const char cr0[8192] = {1, [8191] = 2};
-__attribute__((used, section(".chr_rom_1")))
-const char cr1[8192] = {3, [8191] = 4};
-
 volatile char frame_count;
 
 asm(".section .nmi,\"axR\",@progbits\n"
@@ -22,6 +14,12 @@ void ppu_wait_vblank(void) {
     ;
 }
 
+char write_ppu(unsigned addr, char val) {
+  PPU.vram.address = addr >> 8;
+  PPU.vram.address = (char)addr;
+  PPU.vram.data = val;
+}
+
 char read_ppu(unsigned ppu_addr) {
   (void)PPU.status;
   PPU.vram.address = (unsigned)ppu_addr >> 8;
@@ -31,6 +29,13 @@ char read_ppu(unsigned ppu_addr) {
 }
 
 int main(void) {
+  set_chr_bank(0);
+  write_ppu(0, 1);
+  write_ppu(8191, 2);
+  set_chr_bank(3);
+  write_ppu(0, 3);
+  write_ppu(8191, 4);
+
   // Enable NMI generation.
   PPU.control = 0x80;