ADC sample time varies whle using USB HID rpotocol

[kamransial]

I am using Kiel uvision for arm bare metal example project of  usb device with K20 72 Mhz.I have configured hid to 1 endpoint to send adc data to PC. hid binterval time is 1ms after every 1 ms the PC sends in token to kinetis controller and controller sends 64 bytes of adc data to pc. I have set adc on continuous conversion in interupt mode if i do not connect controller to pc the sample time of adc remains constant but when i connect controller to pc the samples time varies about 10 usec. i want a constant sample time of adc and usb communication in hid

mode together.

[CarlosCasillas · Accepted solution]

Hi Kamran,

Have you verified the ADC conversion time and the ISR duration? Have you checked the duration of the USB transmission function? On some USB tasks, the interrupts are disabled, and during such time, the ADC interrupts will not be serviced. So, you could try implementing DMA transfers for moving the ADC results to a memory buffer at the same time that the USB is transferring the data to the PC.

Hope this will be useful for you.
Best regards!
/Carlos

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