USB Transfer with chained transfer descriptors - slow

[mrharmonsr]

I using the HSUSB on a K61 MCU in device mode.

I'm using firmware based on the old Freescale USB 4.1.1 stack.

I have setup a bulk transfer of 1MByte using several transfer descriptors chained in a list.

The transfer completes correctly.

But I notice a 40 microsecond delay between transfer descriptors. (seen on USB analyzer)

Is this normal?  I expected the USB engine to work much faster than that.

Anyone have any experience with this?  Is this behavior documented?

[mrharmonsr]

I realize now that the time is spent reading the next packet as well as moving to the next transfer descriptor.

My transfer descriptors are in DDR, but I am reading data directly from Flexbus with wait states, so the data transfer is slowing things down.

I am transferring data from Flexbus one packet at a time, because the Flexbus timing is too slow for HSUSB's DMA engine.

Does anyone know the minimum speed of a slave region to support HSUSB transfers?

[Kan_Li]

Hi Larry,

I have heard some customer using external RAM for FSUSB module, but for HSUSB , you'd better use the internal SRAM.

Have a great day,
Kan

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