DSP 56001 Handshaked DMA Communication Example

@DrWatson

Published in 

atari

 · 23 Nov 2023

This example illustrates a typical DSP Handshaked DMA communication program.

; DSP Handshaked DMA IO 
: (C) Fredrik Noring, Tomas Berndtsson 1994 

M_PCC   EQU     $FFE1           ; Port C Control Register 
M_PCDDR EQU     $FFE3           ; Port C Data Direction Register 
M_PCD   EQU     $FFE5           ; Port C Data Register 
M_CRA   EQU     $FFEC           ; SSI Control Register A 
M_CRB   EQU     $FFED           ; SSI Control Register B 
M_RX    EQU     $FFEF           ; Serial Receive Data Register 
M_TX    EQU     $FFEF           ; Serial Transmit Data Register 
M_SR    EQU     $FFEE           ; SSI Status Register 

          org    p:$0 
          jmp    <start 

          org    p:$40 
start     andi    #$fb,omr               ; initialize SSI port 
          movep   #%000000000,x:<<M_PCC  ; SSI reset 
          movep   #%0100000000000000,x:<<M_CRA 
          movep   #%0011010000000000,x:<<M_CRB 
          movep   #%111001000,x:<<M_PCC 
          movep   #%000110000,x:<<M_PCDDR 
          movep   #%000000000,x:<<M_PCD  ; clear frame syncs 

          jsr    <DMA_get    ; Receive DMA data 
          move   #0.27,A     ; Move value to the 56-bits A register 
          move   #0.31415,y0 ; Move value to the 24-bits y0 register 
          mac    x0,y0,A     ; Multiply x0 and y0 and accumulate to A 
          move   A,x0        ; Move the A1 portion of A to x0 
          jsr    <DMA_send   ; Send DMA data 

          jmp    <start      ; Continue 

; DMA I/O routines. 
DMA_send  movep   x0,X:<<M_TX 
          bset    #5,X:<<M_PCD       ; start frame sync 
_wait     jclr    #6,X:<<M_SR,_wait  ; TDE 
          bclr    #5,X:<<M_PCD       ; stop frame sync 
          rts 
DMA_get   bset    #4,X:<<M_PCD       ; start frame sync 
_wait     jclr    #7,X:<<M_SR,_wait  ; RDF 
          bclr    #4,X:<<M_PCD       ; stop frame sync 
          movep   X:<<M_RX,x0 
          rts