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MDK 4 Systick and USB

ian Fox

Hello, I have a working LPC1758 MDK-arm 4 program that is based on the HID example.

When I set the systick to 1ms or less USB enumination fails. At 10ms all is fine, I need 1 ms for other a2d tasks.

Any ideas?

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    Do your other tasks take >1ms, are you spinning in loops?

    What speed is the processor running?

    The Cortex-M3/4 will starve foreground tasks if an interrupt pends before an IRQ Handler completes, it will just tail-chain into the next handler.

    Check what pre-emption state/mode you have in the NVIC, and then what you have set for the IRQ and system handlers. Make sure the SysTick has the lowest priority.

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  • 0

    Do your other tasks take >1ms, are you spinning in loops?

    What speed is the processor running?

    The Cortex-M3/4 will starve foreground tasks if an interrupt pends before an IRQ Handler completes, it will just tail-chain into the next handler.

    Check what pre-emption state/mode you have in the NVIC, and then what you have set for the IRQ and system handlers. Make sure the SysTick has the lowest priority.

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