ChibiOS Free Embedded RTOS

Hi,

That assertion means that a new transaction has been started before the old one has been completed. You should verify in the code. The stack trace should indicate you where the problem happens, see the caller functions.

In 16.1.x there is a new synchronous API for endpoint I/O in the USB driver, using that would prevent this kind of errors.

Giovanni

Thanks, I'll try

My problem was related to a poor PCB design. It was interference between an MCU running on 48 MHz and a USB3300 PHY (they are too close). When I tried the same code on WaveShare board with the same STM32F407 MCU and the same PHY ULPI driver works well. So, I had to finagle with the MCU freq, and it works now on 64MHz.