ZX Spectrum Z80 asm - Attribute brightness checkerboard routine, optimized to size (32B)

AllanTurveyCheckerboard.asm

; Author: Ped7g ; (C) 2021 ; license: https://opensource.org/licenses/MIT
; Z80 assembly, syntax for sjasmplus: https://github.com/z00m128/sjasmplus
; to build: sjasmplus AllanTurveyCheckerboard.asm
    OPT --syntax=abf : DEVICE ZXSPECTRUM48,31999 : ORG $8000

; D:E = field height:width, A = attribute, modifies: AF, HL, BC, IXL
drawCheckerboard:
    ld hl,$5800
.alternateLine
    xor $40     ; alternate BRIGHT 1
    ld ixl,d    ; field height counter
.doNextLine
    push af
    ld c,$20    ; line total length counter
.doLine
    ld b,e      ; field width counter
    xor $40     ; alternate BRIGHT 1
.fillSpan
    ld (hl),a
    inc hl
    dec c
    jr z,.lineDone
    djnz .fillSpan
    jr .doLine
.lineDone
    pop af
    bit 2,h
    ret nz      ; stop at HL == $5C00 (overdraw extra $100 bytes (8 lines))
    dec ixl
    jr nz,.doNextLine
    jr .alternateLine
    DISPLAY "Size of drawCheckerboard routine: ",/D,$-drawCheckerboard

start:
    ld de,$0A05
    ld a,7<<3   ; PAPER 7 : INK 0 : BRIGTH 0 : FLASH 0
    call drawCheckerboard
    jr $
    SAVESNA "checkerboard.sna", start