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POAVR Assembly pure software PWM not giving constant frequency
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  1. POAVR Assembly pure software PWM not giving constant frequency
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    copied!<p>Can someone spot why this code fail to output a constant pulse? At least my Fluke can't trigger on the high pulse, seems like it comes and goes a bit random..</p> <p>This is my first asm program, so keep in mind it could be naive bugs in the code</p> <pre><code>;INITIAL .include "tn10def.inc" ; Include file for Attiny10 .org $0000 rjmp RESET ; ISR reset vector (also start of prog) .org $0008 rjmp WDT ; Watchdog reset vector .def t = r16 ; temp register .def PWM_c1 = r24 ; PWM counter register 1 .def PWM_c2 = r25 ; PWM counter register 2 .def PWM_c3 = r17 ; PWM counter register 3 RESET: ;INIT_STACK: ldi t, low(RAMEND) ; init high and low bytes for stack pointer out spl, t ldi t, high(RAMEND) out sph, t ;INIT_SLEEP: ldi t, (0&lt;&lt;SM2)|(1&lt;&lt;SM1)|(0&lt;&lt;SM0)|(1&lt;&lt;SE) out SMCR, t ; set power down mode at sleep command ;INIT_ISR sei ; enable global interrupts ;INIT_POWERSAVER ldi t, (1&lt;&lt;ADC1D)|(1&lt;&lt;ADC0D) out DIDR0, t ;INIT_CLOCK ldi t, 0xD8 ; write signature out CCP, t ldi t, (1&lt;&lt;CLKPS3)|(0&lt;&lt;CLKPS2)|(0&lt;&lt;CLKPS1)|(0&lt;&lt;CLKPS0) out CLKPSR, t ; prescale by 256 MAIN_LOOP: rcall PWM_INIT rcall POWER_DOWN ; WDT power down rjmp MAIN_LOOP PWM_INIT: ldi PWM_c3, 255 ; total number of pulses PWM_START: sbi PORTB, led ; set out high ldi PWM_c1, 0 ldi PWM_c2, 0 PWM_LOOP: inc PWM_c1 cpi PWM_c1, 16 ; target count (PWM high) breq PWM_OUT_LOW cpi PWM_c1, 208 brne PWM_LOOP ; first loop counts to 208 inc PWM_c2 cpi PWM_c2, 5 brne PWM_LOOP ; second loop counts to 5 dec PWM_c3 brne PWM_START ; counts down number of pulses ret PWM_OUT_LOW: cbi PORTB, led rjmp PWM_LOOP </code></pre>
 

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