the cause of low speed transfer is polling interval | Cypress Semiconductor
the cause of low speed transfer is polling interval
I know why my transfer is so slow. It's the polling interval while slave fifo doesn't have a complet packet.
In my case,I used interrupt transfer mode,ARM clocks datum into slave fifo in 14Mhz,but the USB is so fast that ARM hasn't write a complete packet when USB read out all available datum,so in some time there is no data for reading, then host would wait at least 1ms to read again, but during the interval data overflowed.
So the real working time of USB is small, the transfer is in slow speed also.
Another question: what is the polling intrval of isochronous transfer? and how about the bulk trransfer?