i.MX USB host issue

[bernardxiong]

Hi,  

We have a USB host issue in i.MX 6sx. We connect a FTDI usb device to USB host of i.MX6sx, which is USB2, an EHCI port. 

We found if we send the data to the FTDI (it will send back an ACK, then i.MX6sx send the next data), the interval of two data request is too slow. We need the interval about 1ms. There is a latency timer in FTDI, it can be set from 16ms to 1ms. If it's great than 5ms, it's right. But failed small than 5ms, which is about 7-8ms.

And we compared with the program in PC (connected FTDI usb device to USB host of PC), the 1ms interval is OK. Therefore, we don't know whether some setting should be set in iMX6sx. Thank you.

[CarlosCasillas]

Hi Bernard,

Have you ensured that you are using the last BSP version of the GA release?

Additionally, the USB-serial devices are CDC class, which use Bulk transactions, so, the latency depends of the Host capacity and workload. Besides, are you using the generic CDC driver or a custom one? What about PC-side (regarding the Driver)?

Hope this will be useful for you.
Best regards!
/Carlos
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[bernardxiong]

Thank Carlos, 

We use i.MX6SX USB host, and the USB host is manged by M4 with a modified USB stack from Kinetis. 

It's a generic CDC driver but with the latency timer setting in USB device setup, which is as the same as the PC's.