RGBDS routine for verifying, clearing and loading SRAM in a Game Boy game

GB_SRAM.asm

; Based on nitro2k01's code from https://forums.nesdev.org/viewtopic.php?t=14631
; Changes:
; - Retains all registers, so a call to this routine can be added anywhere
; - Instead of saving all WRAM, just save a set number of bytes (c)
; Usage:
; - On boot, call LoadSRAM (will init and zero SRAM if needed, then load from SRAM)
; - When saving, call SaveSRAM (and then potentially LoadSRAM.sramOK)

LoadSRAM:
  call EnableSram

; Check for validity of SRAM by looking for the name of the game from the ROM header
  ld de, $0134    ; Use the copy of the string that is already in the ROM header
  ld hl, $A000    ; Bottom of SRAM
.verifyLoop
  ld a, [de]     ; Load character from the string in ROM
  or a          ; Zero check. If we reached the end of the string, the signature is valid.
  jr z, .sramOk
  cp [hl]  ; Compare with the SRAM byte.
  inc de
  inc hl
  jr z, .verifyLoop  ; Continue checking the string?
  
  ld de, $0134   ; Use the copy of the string that is already in the ROM header.
  ld hl, $A000    ; Bottom of SRAM
.copySigLoop
  ld a, [de]     ; Load character from the string in ROM.
  ld [hl+], a   ; Copy the byte to SRAM and post-increment the RAM point.
  inc de   ; Increment the ROM pointer.
  or a     ; Zero check. If we reached the end of the string, clear the rest of SRAM instead
  jr nz, .copySigLoop  ; Continue copying the string?
  
.clearSramLoop
  xor a        ; Set the value of a to 00.
  ld [hl+], a  ; Clear the byte to SRAM and post-increment the RAM point.
  ld a, h      ; High byte of pointer
  cp $C0       ; When H=$C0 we have reached outside of SRAM.
  jr nz, .clearSramLoop 
  
.sramOk
  ; The signature matched, or SRAM was cleared. Now copy from SRAM to work RAM
  ld  hl, $A010  ; SRAM location after string
  ld  de, $C130  ; WRAM location, edit this
.copyHiScore
  ld  c, 7       ; Number of bytes
  ; Restore WRAM from the copy in SRAM
.restorehiscoreloop
  ld a, [hl+]
  ld [de], a
  inc de
  
  dec c
  ;ld a, h
  ;cp  $c0  ; Has the source address reached outside $b000-$bfff?
  jr nz, .restorehiscoreloop

  ; Disable SRAM access and return.
  xor a
  ld [$0000], a
  
  pop hl
  pop de
  pop bc
  pop af
  ret

SaveToSRAM:
  call EnableSram

  ; Copy from WRAM to SRAM
  ld  hl, $C120  ; WRAM location, edit this
  ld  de, $A010  ; SRAM location after string

  jp LoadSRAM.copyHiScore

EnableSram:
; Retain registers
  push af
  push bc
  push de
  push hl

; Enable SRAM
  ld a, $0A
  ld [$0000], a
  ret