Objective Development Forums

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uint8_t usbActivity;

int main( void )
{
   ...
   for ( ;; )
   {
      // Wait for 8ms USB interrupt packet
      usbActivity = false;
      do {
         usbPoll();
      }
      while ( !usbActivity );
   
      // Approximate time of USB interrupt
      unsigned frame_begin = clock();
   
      // Give USB plenty of time to do any more packets for this 8ms frame
      while ( clock_elapsed( frame_begin ) < CLOCK_US( 3500 ) )
         usbPoll();
   
      // If LEDs changed, do nothing for this frame as USB tends to be active throughout
      uint8_t new_leds = keyboard_leds;
      if ( old_leds != new_leds )
      {
         old_leds = new_leds;
         continue;
      }
   
      // Poll ADB keyboard
      cli();
      ... ~4ms
      sei();
   }
}


// Modification to usbdrv/asmcommon.inc

#define USB_CFG_ACTIVITY_FLAG 1

...
storeTokenAndReturn:
    sts     usbCurrentTok, token;[35]
#if ! USB_CFG_ACTIVITY_FLAG
doReturn:
#endif
doReturnNoActivity:
    POP_STANDARD                ;[37] 12...16 cycles
    USB_LOAD_PENDING(YL)        ;[49]
    sbrc    YL, USB_INTR_PENDING_BIT;[50] check whether data is already arriving
    rjmp    waitForJ            ;[51] save the pops and pushes -- a new interrupt is already pending
sofError:
    POP_RETI                    ;macro call
    reti
#if USB_CFG_ACTIVITY_FLAG
doReturn:
   ldi     x1, 1
    sts     usbActivity, x1
    rjmp    doReturnNoActivity
#endif

handleData:
#if USB_CFG_CHECK_CRC
    CRC_CLEANUP_AND_CHECK       ; jumps to ignorePacket if CRC error
#endif
    lds     shift, usbCurrentTok;[18]
    tst     shift               ;[20]
    breq    doReturnNoActivity  ;[21]
...

Code: Select all

#define USB_CFG_INTR_POLL_INTERVAL      8 //could set to 1 for 1 ms between polls
/* If you compile a version with endpoint 1 (interrupt-in), this is the poll
 * interval. The value is in milliseconds and must not be less than 10 ms for
 * low speed devices.
 */