;;
;; Driving 7-segment LED displays over SPI
;;

; Output Enable control
.equ LED7_DDR    = DDRB
.equ LED7_PORT   = PORTB
.equ LED7_OE     = PORTB1                ; Output Enable (Low)

; Font for 7-segment display
; Includes decimal digits 0-9, hexadecimal digits A-F, and some special chars
LED7_Font:
.db     0b00111111, 0b00000110      ; 0, 1
.db     0b01011011, 0b01001111      ; 2, 3
.db     0b01100110, 0b01101101      ; 4, 5
.db     0b01111101, 0b00000111      ; 6, 7
.db     0b01111111, 0b01100111      ; 8, 9
.db     0b01110111, 0b01111100      ; A, b
.db     0b00111001, 0b01011110      ; C, d
.db     0b01111001, 0b01110001      ; E, f
.db     0b10000000, 0b00000000      ; ., 

.equ LED7_0     = 0
.equ LED7_1     = 1
.equ LED7_2     = 2
.equ LED7_3     = 3
.equ LED7_4     = 4
.equ LED7_5     = 5
.equ LED7_6     = 6
.equ LED7_7     = 7
.equ LED7_8     = 8
.equ LED7_9     = 9
.equ LED7_A     = 10
.equ LED7_B     = 11
.equ LED7_C     = 12
.equ LED7_D     = 13
.equ LED7_E     = 14
.equ LED7_F     = 15
.equ LED7_DOT   = 16
.equ LED7_EMPTY = 17

; output buffer
.set LED7_COUNT = 2

.dseg
led7_buffer:    .byte LED7_COUNT

.cseg

;; Initialize LCD to empty, and enable
LED7_Init:
    ; Setup ENable port
        sbi         LED7_PORT, LED7_OE    ; Disabled (Low)
        sbi         LED7_DDR, LED7_OE     ; Out
    
    ; Initialize buffer
        ldi         r16, 0b11111111
        sts         led7_buffer + 0, r16
        sts         led7_buffer + 1, r16

    ; Output
        ldi         r16, LED7_COUNT
        ldi         XL, low(led7_buffer + LED7_COUNT)
        ldi         XH, high(led7_buffer + LED7_COUNT)
        rcall       SPI_SendBuf

    ; Enable output once the initial display has been shifted out
        cbi         LED7_PORT, LED7_OE

    ; Done
        ret

LED7_LoadChar:
        clr         r0, 0

    ; Prep address
        ; base addr for font table
        ldi         ZH, high(2 * LED7_Font)
        ldi         ZL, low(2 * LED7_Font)
        
        ; offset
        add         ZL, r8
        adc         ZH, r0

    ; Load char
        lpm         r8, Z

    ; Done
        ret
 
;; Display a single digit on the display
;;  Input: r16, r17
LED7_Show:
        mov         r8, r16
        rcall       LED7_LoadChar
        mov         r16, r8

        mov         r8, r16
        rcall       LED7_LoadChar
        mov         r16, r8
        
    ;; Continue

;; Display a raw segment mask
;;  Input: r16, r17
LED7_ShowRaw:
    ; Set buffer
        sts         led7_buffer + 0, r16
        sts         led7_buffer + 1, r17

    ; Output
        ldi         r16, LED7_COUNT
        ldi         XL, low(led7_buffer + LED7_COUNT)
        ldi         XH, high(led7_buffer + LED7_COUNT)

    ; Display
        rjmp        SPI_SendBuf