code:ground_control
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code:ground_control [2008/10/30 05:18] laurenceb |
code:ground_control [2008/11/13 09:50] (current) laurenceb |
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| ===== Input capture based version ===== | ===== Input capture based version ===== | ||
| + | This uses the input capture function on timer1 (atmega168). The ICNC1 bit in the TCCR1B register need to be set to enable oversampling to give more noise tolerance. A second function running approx every 20ms is needed to decrement counter by two and check if counter>=30. If this is the case there is a valid pwm stream and the diff variable can be used to set the pwm output. | ||
| + | ==== Header ==== | ||
| <code c> | <code c> | ||
| - | volatile u08 counter; //globals | + | void enable_ground_control(); //enables the input capture interrupt |
| - | volatile s16 diff; | + | void disable_ground_control(); //disables input capture interrupt |
| + | #define PULSE_MIN (s16)(0.001*(float)F_CPU/16.0) //pwm must be in the range 1 to 2 ms | ||
| + | #define PULSE_MAX (s16)(0.002*(float)F_CPU/16.0) //due to the bit shift we divide by 16 | ||
| + | #define GROUND_LED_ON PORTD|=(1<<3) | ||
| + | #define GROUND_LED_OFF PORTD&=~(1<<3) | ||
| + | #define GROUND_LED_SET PORTD&(1<<3) | ||
| + | void run_ground_control(); | ||
| + | </code> | ||
| + | ====Main code=== | ||
| + | |||
| + | <code c> | ||
| + | #ifdef GROUND | ||
| + | #include "main.h" | ||
| + | extern volatile u08 counter; //globals | ||
| + | extern volatile u16 diff; | ||
| + | |||
| + | |||
| ISR(TIMER1_CAPT_vect) | ISR(TIMER1_CAPT_vect) | ||
| { | { | ||
| static u16 start; | static u16 start; | ||
| - | if(TCCR1B|0x40) //start of a pulse | + | if(TCCR1B&0x40) //start of a pulse |
| { | { | ||
| TCCR1B&=~0x40; //set to trigger on falling edge | TCCR1B&=~0x40; //set to trigger on falling edge | ||
| - | start=ICP1; //record start of the pulse | + | start=ICR1; //record start of the pulse |
| } | } | ||
| else | else | ||
| { | { | ||
| TCCR1B|=0x40; //set to trigger on rising edge | TCCR1B|=0x40; //set to trigger on rising edge | ||
| - | if(!counter&0x80) //the lock bit isn't set, so we are free to run | + | if(!(counter&0x80)) //the lock bit isn't set, so we are free to run |
| { | { | ||
| - | diff=ICP1-start; //set the global volatile u16 diff | + | diff=ICR1; //set the global volatile s16 diff |
| - | if(start>ICP1) //our pwm pulse spans a timer overflow | + | if(start>diff) //our pwm pulse spans a timer overflow |
| { | { | ||
| diff+=TOP_COUNT; | diff+=TOP_COUNT; | ||
| } | } | ||
| + | diff-=start; | ||
| if(diff>PULSE_MIN && diff<PULSE_MAX) //test against criterion | if(diff>PULSE_MIN && diff<PULSE_MAX) //test against criterion | ||
| { | { | ||
| - | if(counter&0xEF<30) //30 consecutive pulses | + | if((counter&(~0x80))<30) //30 consecutive pulses |
| { | { | ||
| - | counter+=3; //the 20ms timer1 overflow subtracts 2 from counter | + | counter+=3; //the 20ms timer1 overflow subtracts 2 from counter |
| } | } | ||
| } | } | ||
| else | else | ||
| { | { | ||
| - | counter&=0xEF; //set the last 7 bits to zero | + | counter&=0x80; //set the last 7 bits to zero |
| } | } | ||
| } | } | ||
| } | } | ||
| } | } | ||
| + | |||
| + | void run_ground_control() | ||
| + | { | ||
| + | if((~0x80&counter)>=28) | ||
| + | { | ||
| + | counter|=0x80; //lock the diff variable using the counter flag bit | ||
| + | OCR1B=diff; | ||
| + | counter&=~0x80; | ||
| + | GROUND_LED_ON; | ||
| + | } | ||
| + | else | ||
| + | { | ||
| + | GROUND_LED_OFF; | ||
| + | } | ||
| + | if(counter&~0x80) //if the counter variable >0, decrement by 2 | ||
| + | counter-=2; | ||
| + | } | ||
| + | |||
| + | void enable_ground_control() | ||
| + | { | ||
| + | TIMSK1|=(1<<ICIE1); | ||
| + | counter=0; | ||
| + | } | ||
| + | |||
| + | void disable_ground_control() | ||
| + | { | ||
| + | TIMSK1&=~(1<<ICIE1); | ||
| + | GROUND_LED_OFF; | ||
| + | counter=0; | ||
| + | diff=0; | ||
| + | } | ||
| + | #endif | ||
| </code> | </code> | ||
| + | |||
| Line 44: | Line 96: | ||
| - | This AVR code constantly checks the PWM input for pulse lenght. If a stream of 10 pulses are detected that match the criterion, the input PWM in routed to the output. A single failing PWM pulse will cause control to revert back to internal guidance. Useful for UAVs, allowing control to be regained from the ground in the event of a faulty control algorthym. | + | This AVR code constantly checks the PWM input for pulse lenght. If a stream of 10 pulses are detected that match the criterion, the input PWM is routed to the output. A single failing PWM pulse will cause control to revert back to internal guidance. Useful for UAVs, allowing control to be regained from the ground in the event of a faulty control algorthym. |
| ===== ground.h ===== | ===== ground.h ===== | ||
code/ground_control.1225343932.txt.gz · Last modified: 2008/10/30 05:18 by laurenceb
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