6502-OS/system/spi.s65

.include "spi.h65"

Export spi_p, begin, end, read, pages_written, bytes_written

.zeropage
code_page:          .res 2  ; CODE_START + pages_written * 256
.bss
bytes_written:      .res 1
pages_written:      .res 1

SPI_IO := spi_p::SPI_IO
CODE_START := spi_p::CODE_START

; spi-transferred code will be placed here
; SPI_P = as peripheral
.code
.struct SPI_P_Pins
    ; VIA addresses
    DDR_a   .word   ; address of the data direction register
    R_a     .word   ; address of the register
    ; pin mask
    SCLK_p  .byte   ; Serial Clock
    POCI_p  .byte   ; Peripheral Out / Controller In
    PICO_p  .byte   ; Peripheral In / Controller Out
    CSB_p   .byte   ; Chip Select
    ; settings
    CPOL    .byte   ; Clock Polarity
    CPHA    .byte   ; Clock Phase
.endstruct

;********************************************************************************
; @function Begin listening for SPI transfers
; @details
;   - initialize variables
;   - configure shift register to shift in under external clock
;   - enable shift register interrupts 
;********************************************************************************
.proc begin
    stz pages_written
    stz bytes_written
    ; store address in zp
    lda #<CODE_START
    sta code_page
    lda #>CODE_START
    sta code_page + 1
    ; todo USE MASKS
    ; set Shift register to shift in under external clock on CB1
    lda #IO::ACR::SR_SIN_PHIE
    sta SPI_IO + IO::ACR

    ; enable SR interrupts
    lda #(IO::IRQ::IRQ | IO::IRQ::SR)
    sta SPI_IO + IO::IER

    ; load SR to reset
    lda SPI_IO + IO::SR
    rts
.endproc


;********************************************************************************
; @function Stop listening for SPI transfers
; @details
;  Disables shift register interrupts
; @modifies A
;********************************************************************************
.proc end
    ; disable SR interrupts
    lda #IO::IRQ::SR
    sta SPI_IO + IO::IER
    rts
.endproc


;********************************************************************************
; @function Read a byte from SPI
; @details
;  Reads a byte from the shift register and stores it in the SPI code buffer
; @modifies A,Y
;********************************************************************************
.proc read
    ldy bytes_written
    lda SPI_IO + IO::SR
    sta (code_page),y
    inc bytes_written
    beq @new_page
    rts
@new_page:
    inc pages_written
    inc code_page + 1
    rts
.endproc

    
;********************************************************************************
; @function Initialize the IO Adapter for SPI
; @param ARG0-1 Address of the SPI_Pins struct
;********************************************************************************
;********************************************************************************
; @function Read bytes
; @param X Number of bytes to send
; @param ARG0-1 Address of the SPI_Pins struct
; @param ARG2-3 Address of the first byte
;********************************************************************************
.proc recv_data
.endproc
;********************************************************************************
; @function Send bytes
; @param X Number of bytes to send
; @param ARG0-1 Address of the SPI_Pins struct
; @param ARG2-3 Address of the first byte
;********************************************************************************
.proc send_data
.endproc