In Serial Downloader mode, download using USB, PC does not link to USB

[353533661]

In my design, i.mx6ul's UART2_RXD, UART4_RXD, UART5_RXD connected to other MCUs of UART.Internal Boot start-up, i.mx6ul and MCU's UART data communication is no problem.
When in Serial Downloader mode, and this MCU is working, using USB download, the PC does not link to USB.
If the MCU stops working, the PC can link to USB and download it complete.
Is there a BUG in i.mx6ul?

[igorpadykov]

Hi xiaojun

according to Figure 8-2. Serial Downloader boot flow

i.MX 6UltraLite Applications Processor Reference Manual

both uart and usb are polling by ROM. So uart activity may prevent

PC link to USB.

Best regards
igor
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