; -*-asm-*-


        BRA r :reset ; RESB
        BRA r :irq   ; IRQB

irq:    PHA s
        LDA a %10000000
        STA a 800d
        PLA s
        RTI s

        ;; reset stack
reset:  SEI i

        LDX # ff
        TXS i

        ;; xxxSSSxx
        LDA # 18
        STA a 800b

        LDA # %10000000
        STA a 8001

        ;; CS SCLK DO x x x x x
        LDA # %11100000
        STA a 8003

        ;; LDA # %01111111
        ;; STA a 800e

        ;; LDA # %10000100
        ;; STA a 800e

        ;; low byte
        LDX # %11000000         ; write conf
        LDY # %00000001
        JSR a :spi16

        LDX # %10000000         ; write data
        LDY # 6c
        JSR a :spi16

forever: BRA r :forever

        ;; CS low
spi16:  LDA # %00000000
        STA a 8001

        STX zp 2
        STY zp 1

        LDX # 2
_spi_next:      LDY # 8
_spi_8:         CLC i
                ASL zp,x 0
                LDA # %00000000 ; clear DO
                BCC r :_spi_z
                ORA # %00100000 ; set DO
_spi_z:         STA a 8001
                NOP i
                ORA # %01000000 ; set SCLK
                STA a 8001
                AND # %10111111 ; clear SCLK
                STA a 8001
                DEY i
                BNE r :_spi_8
                DEX i
                BNE r :_spi_next
        ;; CS high
        LDA # %10000000
        STA a 8001
        RTS s