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loop time

 
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beaker404



Joined: 24 Jul 2012
Posts: 163

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loop time
PostPosted: Fri May 24, 2019 9:55 am     Reply with quote

working on a high speed ADC project. checking my loop time by using a toggle of a pin. In this case J5. just running the toggle the loop time is 500nS.
when I add a call to this code the loop time goes to 250uS:

Code:

int ADS8584S_START_ACQ() {
// This function starts the ACQ process on the ADS8584S
// CONVSTA and CONVSTB are tied together, use CONVSTA for control.


   
   

    int loop_control = 1;                      // used to control while loop.
   int status = 0;
   int16 t1_start = 0;
    int16 t1_difference = 0;
    int16 t1_end = 0;                   // Timer1 running at 20KHz (50uS per count)

   
   
   output_high(ADC_CONVSTA);
    //delay_us(ADC_DELAY);                     // 2uS delay
    output_low(ADC_CONVSTA);
}


as noted in the comments, I am running timer1 at 20KHz roll rate. but have that code commented out at this time.
ADC_CONVSTA is on PIN_J1
I am surprised that the calls to output_high and output_low take so long.

any ways to speed it up?

18F87K22 running at 60MHz.

CCS 5.061
MPLAB 8.91
windows 10
beaker404



Joined: 24 Jul 2012
Posts: 163

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PostPosted: Fri May 24, 2019 9:58 am     Reply with quote

correction, loop time is 1.05mS not 250uS.
beaker404



Joined: 24 Jul 2012
Posts: 163

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PostPosted: Fri May 24, 2019 10:11 am     Reply with quote

well scrubbed the code and found a random delay_ms(1) call that I forgot to take out.
code runs much faster now. still interested in how to speed code up specifically if there are tricks with the digital I/O to make the output_high output_low calls faster as I am banging pins for CS control of the ADC.

also, using a crude way to build my data word from the 16 bit parallel output of the ADC. the data pins are going to I/O pins on the pic and using the following code for that, interested if there are faster ways to do this without redoing my hardware.
Code:

int16 ADS8584S_BUILD_CHANNEL_VALUE() {

int16 value=0;

if(input(ADC_D15) == 1) {      // 32768

   value = value + 32768;

}

if(input(ADC_D14) == 1) {

   value = value + 16384;

}

if(input(ADC_D13) == 1) {

   value = value + 8192;

}

if(input(ADC_D12) == 1) {

   value = value + 4096;

}

if(input(ADC_D11) == 1) {

   value = value + 2048;

}

if(input(ADC_D10) == 1) {

   value = value + 1024;

}

if(input(ADC_D9) == 1) {

   value = value + 512;

}

if(input(ADC_D8) == 1) {

   value = value + 256;

}

if(input(ADC_D7) == 1) {

   value = value + 128;

}

if(input(ADC_D6) == 1) {

   value = value + 64;

}

if(input(ADC_D5) == 1) {

   value = value + 32;

}

if(input(ADC_D4) == 1) {

   value = value + 16;

}

if(input(ADC_D3) == 1) {

   value = value + 8;

}

if(input(ADC_D2) == 1) {

   value = value + 4;

}

if(input(ADC_D1) == 1) {

   value = value + 2;

}

if(input(ADC_D0) == 1) {

   value = value + 1;

}

return value;

}  // end BUILD_CHANNEL_VALUE()
alan



Joined: 12 Nov 2012
Posts: 349
Location: South Africa

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PostPosted: Fri May 24, 2019 10:42 am     Reply with quote

You can use the FAST_IO directive as well as a union.

with FAST_IO and union
Code:
value_test.val0 = input(PIN_A0);
010A:  BCF    40.0
010B:  BTFSC  0C.0
010C:  BSF    40.0

with FAST_IO and your method
Code:
................... if(input(PIN_A0) == 1) {      // 32768
00A8:  BTFSS  0C.0
00A9:  GOTO   0AC
....................    value = value + 32768;
00AA:  MOVLW  80
00AB:  ADDWF  43,F

without FAST_IO and union
Code:
.................... value_test.val11 = input(PIN_C1);
012E:  MOVLB  01
012F:  BSF    0E.1
0130:  MOVLB  00
0131:  BCF    41.3
0132:  BTFSC  0E.1
0133:  BSF    41.3

without FAST_IO and your method
Code:
.................... if(input(PIN_C0) == 1) {
00D4:  MOVLB  01
00D5:  BSF    0E.0
00D6:  MOVLB  00
00D7:  BTFSS  0E.0
00D8:  GOTO   0DD
....................    value = value + 32;
00D9:  MOVLW  20
00DA:  ADDWF  42,F
00DB:  MOVLW  00
00DC:  ADDWFC 43,F
temtronic



Joined: 01 Jul 2010
Posts: 9081
Location: Greensville,Ontario

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PostPosted: Sat May 25, 2019 4:43 am     Reply with quote

I'm wondering if instead of adding to'value', you bitset 'value' bits based on the testing, if it'd be faster?
I recall a uChip app note or tips 'n tricks about doing that....
Though it's been decades since I read that in a real book.....

hmm...raining cats, dogs and giraffes here so I cut some code...
got this which looks like it shaves off some time and space !
Code:

190:               if(input(ADC_D15) == 1) bit_set(value,15);
  0662    8292     BSF 0xf92, 0x1, ACCESS
  0664    B280     BTFSC 0xf80, 0x1, ACCESS
  0666    8E1B     BSF 0x1b, 0x7, ACCESS

though someone can test, I've got a leaky gutter to fix...arrgh

Jay
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