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damiencourousse
Joined: 23 Mar 2006
Posts: 13
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 Posted: Fri Jan 26, 2007 3:29 am Post subject: Input/Output delay with the Servo example |
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Hello,
We experience a strange behavior of the Servo class, using an external clock for the synchronization of the D/A & A/D conversion triggering:
About 50% of the time, there is NO delay between Input and Output,
and 50% of the time, there is a delay of one CLK period between Input and Output (which should be the correct behavior).
This is illustrated in the file attached: Input triangular signal in black, output signal in red.
Each of these cases happen randomly as I launch the Servo application.
here is below the code of the main cpp file:
the interrupt handler:
| Code: |
/******************************************
INT7 Handler
******************************************/
extern "C"
{
#pragma CODE_SECTION(".onchip");
void interrupt II_EINT7_IntHandler()
{
float float_buff[NUM_CHANNELS];
short short_buff[NUM_CHANNELS];
volatile short * buff;
volatile short * buff_ptr;
register int i;
register float i_temp;
static volatile float t=0;
myServoPtr->TransferIn_8pair(); /* adapter selon le nb de canaux engagés */
myServoPtr->TransferOut_8pair(); /* adapter selon le nb de canaux engagés */
}
} // end extern "C"
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and the main function:
| Code: |
/************************************************
IImain()
*************************************************/
void IIMain()
{
HWI_disable();
// Create and configure timebase object
BasicTmb Timebase;
Timebase.Rate(SampleRate);
//Timebase.ClockSource( csDds );
Timebase.ClockSource( csExternal );
Timebase.Stop();
//
// Create Servo object
TestServo ServoIo(intEInt7);
myServoPtr = &ServoIo;
//
// Attach Timebase to servo
ServoIo.AdcDev().Attach(Timebase);
//
// Configure Servo
//
// ...Enable all channels for input & output
//int ServoChannels = HardwareInfo()->DacChannels();
for (int ch=0; ch<NUM_CHANNELS; ch++)
{
ServoIo.ChannelEnabled(ch, true);
}
//
// ...Configure delay of DAC clock
ServoIo.Delay(0);
// Attente de la confirmation host pour lancer la boucle Servo
ServoIo.Open();
ServoIo.Start();
HWI_enable();
// Attente du message d'arret de la part du host
while ( !(*p_host_msg== TD_STOP))
{
*p_dsp_msg=DSP_WAIT_STOP;
// MAJ_Params();
}
*p_host_msg = TD_NULL;
*p_dsp_msg= DSP_ACK;
// Arret de la boucle Bypass
ServoIo.Close();
}
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jhenderson
Site Admin
Joined: 07 Mar 2006
Posts: 1177
Location: So. Cal. USA
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| Posted: Mon Jan 29, 2007 5:22 am Post subject: Servo delay |
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It is theoretically impossible for the servo delay to be zero. So, I suspect that you are really seeing a 360 degree phase shift,
The most likely source of the problem lies in the triggering. The Matador cards can utilize an external clock, but should not commence data flow until the A/D and D/A are triggered. The EngineCtl class contains methods that you should be using to start the triggers for both the A/Ds and D/As simultaneously. If this is done properly, and the servo calculations can be performed in the allotted servo interval, you should eliminate the phase error.
_________________
Jim |
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