USB OTG issue. I am working on a project port that uses an STM32F407ZGT that communicates with a PC via a USB VCP. The original implementation used an FTDI USB chip to provide a VCP. We have a simple command, response protocol to talk to the STM32. For the most part, the VCP works well. A command gets sent from the PC to the STM32, gets processed and then replies. On average, a round trip takes around 1ms depending on the command. Occasionally, we will get a delay of about 1 second from when one command completes to when the next command arrives. We have instrumented the code on both the PC sides and the STM32 side, and it appears that the issue is on the STM32 side.
We are using a while loop, interrupt-based architecture. Interrupts are all running at the same priority level in an effort minimize any contention of resources. I’m quite sure it’s a timing issue in our firmware, but I need to ask the question, has anyone seen sporadic time delays using the VCP part of the library?
