Objective Development Forums

Code: Select all

    switch(rq->bRequest)
   {
       case CMD_ADC_READ:         
         usbMsgPtr = (uchar *)&ADC;

         return 2;
...

Code: Select all

volatile uint8_t adcbuff[250]; // must be multiple of 5 for 10 bit mode
volatile uint8_t end = 0;
volatile uint8_t start = 0, bytes_ready;
volatile uint8_t adc_10bit_mode = 0;

#define ADCBufferSize()      ((end - start + DAC_BUFF_SIZE) % DAC_BUFF_SIZE)
#define ADCBufferFull()      ((end + 1) % DAC_BUFF_SIZE == start)
#define ADCBufferClear()   end = 0; start = 0

ISR(ADC_vect, ISR_NOBLOCK)
{
   uint8_t high_byte, shift_amount;

   if(ADCBufferFull())
   {
      // throw away oldest samples if buffer is full

      if(adc_10bit_mode)
         start = (start + 5) % DAC_BUFF_SIZE;
      else
         start = (start + 1) % DAC_BUFF_SIZE;
   }

   if(adc_10bit_mode)
   {
      // pack four 10 bit samples into 5 bytes by using every 5th byte to store the 2 LSB's of the previous 4 samples

      // skip every 5th byte
      if((end + 1) % 5 == 0)
         end = (end + 1) % DAC_BUFF_SIZE;

      high_byte = end + 5 - ((end + 1) % 5); // find index of byte to store 2 LSB's
      shift_amount = 6 - (end % 5)*2;       // find bit position in byte to store the 2 bits

      adcbuff[high_byte] = (adcbuff[high_byte] & ~(0b11000000 >> shift_amount)) | (ADCL >> shift_amount);
   }

   adcbuff[end] = ADCH;
   end = (end + 1) % DAC_BUFF_SIZE;

   TIFR |= (1 << OCF0A); // clear interrupt flag
}

Code: Select all

usbMsgLen_t usbFunctionSetup(uchar setupData[8])
{
    usbRequest_t *rq = (void *)setupData;
   static uchar buf;

    switch(rq->bRequest)
   {

// <more non essential commands here>

      case CMD_ADC_BUFFER_READ:
         bytes_ready = MIN(ADCBufferSize(), rq->wValue.bytes[0]);
         
         if(adc_10bit_mode)
            // need to send 5 bytes at a time in 10 bit mode
            bytes_ready = (bytes_ready/5)*5; 

         return USB_NO_MSG;
            
      case CMD_ADC_BUFFER_CLEAR:
         ADCBufferClear();

         return 0;

      case CMD_ADC_SAMPLERATE_SET:
         ADCSampleRateSet(rq->wValue.bytes[0]);

         return 0;
}

Code: Select all

uchar usbFunctionRead(uchar *data, uchar len)
{
    if(len > bytes_ready)
        len = bytes_ready;

    for(uint8_t i = 0; i < len; ++i)
        data[i] = adcbuff[(i + start) % DAC_BUFF_SIZE]; // copy data to ADC buffer

   start = (start + len) % DAC_BUFF_SIZE;
   bytes_ready -= len;

   return len;
}