How does USB reach the high speed of theory

[迷足迷]

Hello,

      I use IMX28's USB0 as a custom HID device. At the initial time, the maximum speed of transmission reaches 900KB/S. After modifying the register USBCMD's ITC, the interrupt response time is changed to the immediate response. Now the speed can reach 2MB/S, but the speed is still no more than 8MB/S. How should we do it, and continue to improve the speed?

[joanxie]

maybe you can set the PFSC bit (bit 24) in the PORTSC register during usb controller init and prior to setting the RS bit in the USBCMD register (start controller), the port will work in full speed only. this isn't supported current bsp, so one need to do this manually.

[迷足迷]

Hi Joan Xie,

    Thank you very much for your reply. The reference manual indicates that the default value of PFSC is 0, that is, USB is high speed, and if you write 1 to that bit, it will force the USB to be full speed. At the same time, through the USB analyzer capture, can be seen, PC identified imx283 development board is a high speed equipment, so there is not any other reason?