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Very high irq rate when using USB OTG in host mode

Question asked by john noyb on Jan 6, 2017

Hi all,

I am using the STM32F427ZI with the CubeMX USB OTG Host library V3.2.1. under FreeRTOS v8.2.1.
Even when the system is idle, there are continuous USB interrupts running at a very high rate. Each ISR takes 24us to process but repeats at 30us intervals so there is only 6us left for any other processing.
Most of the interrupts are "Host channels interrupt", but roughly one in 50 is Start of Frame.
The interrupt is a receive of a NAK, which I understand to mean that the host has sent an invitation (IN token) and the slave has replied with a NAK meaning no data to send at this time.

 

Should the host be sending invitations at this rate?
Is there a way to slow this down without breaking the USB comms?

My actual message rate is very low and the amount of data tiny so there would be no problems with a far lower rate from my applications viewpoint.

 

I raised this with the STM support line but got no answer so any support from the community would be gratefully received.

 

John

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