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;; Basic LED matrix fonts

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;; vim: set ft=avr:

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.cseg

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;; Font definition

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; Defines FONT_8x6 symbol

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.include "font.def"

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; Font to use

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.set FONT_TABLE     = FONT_8x6

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.set FONT_START     = FONT_8x6_START

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.set FONT_END       = FONT_8x6_END

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.set FONT_COLS      = FONT_8x6_COLS

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.set FONT_ROWS      = FONT_8x6_ROWS     ; XXX: fixed to 8

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;; Render the given ASCII char into the given buffer

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; Input:    r16 - ASCII char code

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;           Y   - dest buf (Wx8 column data)

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Font_Render:

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    ; Test char index

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        ; test under-range

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        ldi     r17, FONT_START

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        cp      r16, r17

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        brlt    f_render_invalid

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        ; test over-range

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        ldi     r17, FONT_END

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        cp      r17, r16

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        brlt    f_render_invalid

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    ; Locate font char

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        ; compute offset in chars (r16)

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        subi    r16, FONT_START

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        ; compute offset in bytes (r1:r0)

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        ldi     r17, FONT_COLS

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        mul     r16, r17

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        ; font table start offset from words

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        ldi     ZL, low(FONT_TABLE * 2)

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        ldi     ZH, high(FONT_TABLE * 2)

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        ; apply offset

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        add     ZL, r0

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        adc     ZH, r1

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    ; Copy column pixel data

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        ; count columns

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        ldi     r16, FONT_COLS

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f_render_cpy:

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        ; copy via r17

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        lpm     r17, Z+

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        st      Y+, r17

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        dec     r16

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        brne    f_render_cpy

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f_render_invalid:

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    ; Done

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        ret

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