[Paparazzi-devel] module period accuracy ???

[Chris]

Hi.
I have made some tests using CHDK and a Canon SX230HS and it "almost" 
works ok but i do
have some small problems.
I want to ask anyone that might know if the module period is accurate 
enough or it might miss
or skip some cycles especially during intialization of the autopilot.
I have wrote the module code and the chdk script and it works flawlessly 
in pulse count mode
where the camera camera counts the number of pulses and decides what to 
do but it is a slow
process. In this mode module period accuracy does not matter thus it 
works fine.
In pulse duration mode which is very fast my pulses during the autopilot 
initialization
are all over the place but i haven't checked what happens during normal 
operation,
maybe during intialization some things take more time which would 
explain the inaccuracy.
Some times it works fine, other times some pulses get longer like the 
call to the module's
periodic function (@ 15 Hz) is delayed.
I am now searching of a way to use a spare autopilot timer otherwise 
there is always the I2C -> PW
converter option using a small AVR (attiny85) or a spare ppm encoder.
Here is the periodic function:

void chdk_periodic(void){

uint8_t x = 0;

if (chdk_command > 0){
   // Since this variable is ment for Joystick camera control where the 
operator
   // has visual confirmation of each command execution there is no 
need for a buffer.
   // If the buffer is completely empty execute the new command else 
try again...
   for (x=0; x<sizeof(cmd_buffer); x++){
       if (cmd_buffer[x] != 0){
          break;

       }else{ *cmd_buffer = chdk_command; }
   }
   chdk_command = 0;
}

if (cmd_buffer[0] > 0){

   if (command_finished == TRUE){
      pulse_counter = *cmd_buffer;
      reset_counter=CHDK_RESET_CYCLES;
      command_finished = FALSE;
   }

   if (pulse_counter > 0){
      LED_OFF(12);  //LED_ON=Low. LED_OFF=High.
      pulse_counter--;

   }else{
           LED_ON(12);
           if (reset_counter <= 0){
              // Shift left the whole buffer one position
              for (x=1; x<COMMAND_BUFFER_SIZE; x++){ cmd_buffer[x-1] = 
cmd_buffer[x]; }
              cmd_buffer[COMMAND_BUFFER_SIZE-1] = 0; // set last buffer 
slot to 0
              command_finished = TRUE;

           }else{ reset_counter--; }
        }
}

return;
}


uint8_t chdk_cmd(uint8_t cam_cmd)
{
uint8_t x = 0;

if (cam_cmd == CHDK_CLEAR_BUFFER){
   for (x=0; x<COMMAND_BUFFER_SIZE; x++){
       cmd_buffer[x]=0;
   }
   pulse_counter = 0;
   reset_counter = 0;
   command_finished = TRUE;

}else{
           // Find an empty slot in the buffer
           for (x=0; x<COMMAND_BUFFER_SIZE; x++){
               if (cmd_buffer[x]==0){ break; }
           }
           if(x != COMMAND_BUFFER_SIZE){ cmd_buffer[x] = cam_cmd; } // 
register the command
     }


return(0);
}