;; Basic LED matrix fonts
;; vim: set ft=avr:

.cseg

;; Font definition
; Defines FONT_8x6 symbol
.include "font.def"

; Font to use
.set FONT_TABLE     = FONT_8x6
.set FONT_START     = FONT_8x6_START
.set FONT_END       = FONT_8x6_END
.set FONT_COLS      = FONT_8x6_COLS
.set FONT_ROWS      = FONT_8x6_ROWS     ; XXX: fixed to 8

;; Render the given ASCII char into the given buffer
; Input:    r16 - ASCII char code
;           Y   - dest buf (Wx8 column data)
Font_Render:
    ; Test char index

        ; test under-range
        ldi     r17, FONT_START
        cp      r16, r17
        brlt    font_r_invalid

        ; test over-range
        ldi     r17, FONT_END
        cp      r17, r16
        brlt    font_r_invalid

        ; compute offset in chars (r16)
        subi    r16, FONT_START

        ; ok
        rjmp    font_r_render

font_r_invalid:
        ; use first sym
        ldi     r16, 0

    cbi         PORTD, PIND7

font_r_render:
        ; compute offset in bytes (r1:r0)
        ldi     r17, FONT_COLS
        mul     r16, r17

        ; font table start offset from words
        ldi     ZL, low(FONT_TABLE * 2)
        ldi     ZH, high(FONT_TABLE * 2)

        ; apply offset
        add     ZL, r0
        adc     ZH, r1

    ; Copy column pixel data
        ; count columns
        ldi     r16, FONT_COLS
font_r_cpy:
        
        ; copy via r17
        lpm     r17, Z+
        st      Y+, r17

        dec     r16
        brne    font_r_cpy


    ; Done
        ret