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Direct Memory Access Using the HOLD Operation
4-28
Example 4–1. An Interrupt Service Routine Supporting INT1 and HOLD
.mmregs ;Include c2xx memory–mapped registers.
ICR .set 0FFECh ;Define interrupt control register in I/O space.
ICRSHDW .set 060h ;Define ICRSHDW in scratch pad location.
* Interrupt vectors *
reset B main ;0 – reset , Branch to main program on reset.
Int1h B int1_hold ;1 – external interrupt 1 or HOLD.
.space 40*16 ;Fill 0000 between vectors and main program.
main: SPLK #0001h,imr ;Enable HOLD/INT1 interrupt line.
CLRC INTM
wait: B wait
*********Interrupt service routine for HOLD logic*****************************
int1_hold:
; Perform any desired context save.
LDP #0 ;Set data–memory page to 0.
IN ICRSHDW, ICR ;Save the contents of ICR register.
LACL #010h ;Load accumulator (ACC) with mask for MODE bit.
AND ICRSHDW ;Filter out all bits except MODE bit.
BCND int1, neq ;Branch if MODE bit is 1, else in HOLD mode.
LACC imr, 0 ;Load ACC with interrupt mask register.
SPLK #1, imr ;Mask all interrupts except interrupt1/HOLD.
IDLE ;Enter HOLD mode. Issues HOLDA, and puts
;buses in high impedance. Wait until
;rising edge is seen on HOLD/INT1 pin.
SPLK #1, ifr ;Clear HOLD/INT1 flag in interrupt flag register
;to prevent re–entering HOLD mode.
SACL imr ;Restore interrupt mask register.
; Perform necessary context restore.
CLRC INTM ;Enable all interrupts.
RET ;Return from HOLD interrupt.
int1: NOP ;Replace these NOPs with desired int1 interrupt
NOP ;service routine.
; Perform necessary context restore.
CLRC INTM ;Enable all interrupts.
RET ;Return from interrupts.