diff options
Diffstat (limited to 'src/home/clear_sram.asm')
| -rw-r--r-- | src/home/clear_sram.asm | 74 |
1 files changed, 74 insertions, 0 deletions
diff --git a/src/home/clear_sram.asm b/src/home/clear_sram.asm new file mode 100644 index 0000000..a899b08 --- /dev/null +++ b/src/home/clear_sram.asm @@ -0,0 +1,74 @@ +; validate the saved data in SRAM +; it must contain with the sequence $04, $21, $05 at s0a000 +ValidateSRAM: + xor a + call BankswitchSRAM + ld hl, $a000 + ld bc, $2000 / 2 +.check_pattern_loop + ld a, [hli] + cp $41 + jr nz, .check_sequence + ld a, [hli] + cp $93 + jr nz, .check_sequence + dec bc + ld a, c + or b + jr nz, .check_pattern_loop + call RestartSRAM + scf + call Func_4050 + call DisableSRAM + ret +.check_sequence + ld hl, s0a000 + ld a, [hli] + cp $04 + jr nz, .restart_sram + ld a, [hli] + cp $21 + jr nz, .restart_sram + ld a, [hl] + cp $05 + jr nz, .restart_sram + ret +.restart_sram + call RestartSRAM + or a + call Func_4050 + call DisableSRAM + ret + +; zero all SRAM banks and set s0a000 to $04, $21, $05 +RestartSRAM: + ld a, 3 +.clear_loop + call ClearSRAMBank + dec a + cp -1 + jr nz, .clear_loop + ld hl, s0a000 + ld [hl], $04 + inc hl + ld [hl], $21 + inc hl + ld [hl], $05 + ret + +; zero the loaded SRAM bank +ClearSRAMBank: + push af + call BankswitchSRAM + call EnableSRAM + ld hl, $a000 + ld bc, $2000 +.loop + xor a + ld [hli], a + dec bc + ld a, c + or b + jr nz, .loop + pop af + ret |