; FRISC PIO io unit example
; =========================
;
; A FRISC PIO unit is mapped to 4 word-length
; locations starting from 0xFFFF0000 and is
; attached to INT0. However, the unit is not
; working in interrupt mode.
; 
; The program reads data 40 times from the PIO
; unit and stops the processor once done.

PIOC `EQU 0FFFF0000
PIOD `EQU 0FFFF0004
PIOACK `EQU 0FFFF0008
PIOEND `EQU 0FFFF000C

; initialize PIO unit
; 0=mode IN ; 0=NOT INT ; 1=ICR

 `ORG 0 

 MOVE %B 001, R0
 STORE R0, (PIOC)

; initialize variables for storing data
; and data counter

 MOVE DATA, R1
 MOVE 40, R4

; wait until PIO unit is ready

WAIT
 LOAD R0, (PIOC)
 AND R0, 1, R0
 JP_Z WAIT

; acknowledge ready status and read data

 STORE R0, (PIOACK)
 LOAD R0, (PIOD)
 STOREB R0, (R1) 
 
; signal end of data transfer and check
; if more data should be read
 
 STORE R0, (PIOEND)
 ADD R1, 1, R1
 SUB R4, 1, R4
 JP_NZ WAIT
 HALT 

; data space

DATA `DS 40