topic Re: MIMXRT1176 USB HOST Controller limited to 30Mbps transfer in HS mode in i.MX RT Crossover MCUs

MIMXRT1176 USB HOST Controller limited to 30Mbps transfer in HS mode

nl — Tue, 24 Mar 2026 07:00:44 GMT

Hi,

I am currently working on a USB host controller, high speed 480Mbsp, CDC ACM, 512 bytes Bulk transfer, driver with MIMXR1176. However, I have lower performance than expected (I am testing using USB1 as host and USB2 as device)

It seems often only one bulk transfer of 512 bytes is executed per micro-frame each 125us resulting in 8 * 512Bytes / 125us = 32Mbsp. I monitored the time between enabling async scheduler and entering the ISR and can see ~100us interval but also regularly <1ms interval which confirm one bulk transfer per micro-frame.

I have nothing in the periodic scheduler, only the async scheduler is used.

USBSTS register doesn't return any error when entering the ISR callback. Cerr in qtd is always 3. I can see NAKs were returned as qtd's NaKCnt value decreased (never 0) but I would expect the async scheduler to retry the transaction after AsyncSchedSleepTime instead of stopping until the next micro-frame?

Re: MIMXRT1176 USB HOST Controller limited to 30Mbps transfer in HS mode

EdwinHz — Tue, 24 Mar 2026 18:57:11 GMT

Hi @nl,

If you only queue one QTD at a time, the host controller empties the async schedule and becomes idle until you re‑enable it. This is likely why you see large gaps (1 ms) between transactions. Instead of posting one 512‑byte QTD, queue 8–32 QTDs to keep the async schedule from going empty.

Let me know if this helps.

BR,
Edwin.

Re: MIMXRT1176 USB HOST Controller limited to 30Mbps transfer in HS mode

nl — Mon, 30 Mar 2026 00:08:37 GMT

Hi @EdwinHz ,

Thank you very much, it helped. I was queuing only one large QTD of 8 * 512 bytes for each transmission but queuing 8 QTDs of 8 * 512 bytes solved the issue.