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To keep very accurate timing during ACTIVE and IDLE modes I would like to push the core into IDLE mode and pull it out within Timer0. When I try to do this the system hangs. If I simply set a flag and have the main loop set PCON.IDLE it works fine. It is written in assembler and I am checking the push/pop stuff. I think the problem is in RETI. What happens to the hardware with RETI? Any help or pointers would be great.
Hi Michael, There are some problems with the code you have posted, your routine ?enter_idle does things in the wrong order, the POP PSW and POP ACC will NEVER be executed because the processor is in idle mode so obviously? the stack will eventually overflow and may cause problems in other parts of your program. You also need to remove the Timer0 ISR return address off the stack so if you modify your code from where timer is reloaded to be as follows it should work better for you.
MOV TH0,#TIMER0_ACTIVE_H ; set Timer0 counters MOV TL0,#TIMER0_ACTIVE_L POP AR7 POP AR6 ; Put return address to code on stack MOV A, #LOW(?enter_idle) PUSH ACC MOV A, #HIGH(?enter_idle) PUSH ACC RETI ?enter_idle: POP PSW POP ACC DEC SP ;remove original 'return from interrupt' address DEC SP ORL X32CON,#01H ; switch to 32kHz clock ; wait 3 clock periods (3/4 of a instruction cycle) for glitch ; free operation, Datasheet p33 NOP MOV RFMAIN,#03EH ; power down the RF and main osc ORL PCON, #0x01 ; Enter idle mode NOP ; For safety ; RET ; Can never be executed! END