C6748's USB 2.0 Port : Very low data transfer rate

Hi,

Please refer the TI wiki to know the USB performance,

http://processors.wiki.ti.com/index.php/StarterWare_USB#Performance

http://processors.wiki.ti.com/index.php/StarterWare_01.10.01.01_User_Guide

Dear Titus,

First thank you for you prompt reply and information. :)

The following performance looks nice:

It's a good reference for the performance of Starterware's USB library. However, it's just for USB MSC on AM335X, not for USB CDC on C6748. Anyway, what I expect is to know how to improve the performance of USB CDC on C6748. For example, I noticed that the Maximum Packet Size of CDC is only 64 Byte (for Bulk enpoint):

bEndpointAddress: 0x01 -> Direction: OUT - EndpointID: 1
bmAttributes: 0x02 -> Bulk Transfer Type
wMaxPacketSize: 0x0040 = 0x40 max bytes

bEndpointAddress: 0x81 -> Direction: IN - EndpointID: 1
bmAttributes: 0x03 -> Interrupt Transfer Type
wMaxPacketSize: 0x0010 = 1 transactions per microframe, 0x10

bEndpointAddress: 0x82 -> Direction: IN - EndpointID: 2
bmAttributes: 0x02 -> Bulk Transfer Type
wMaxPacketSize: 0x0040 = 0x40 max bytes

If it is possible to increase this to, e.g., 256 Byte, maybe the performance would be drastically increased?  I'm wondering if anyone in TI who is familiar with Startware's USB library could advise?

Regards,

Oliver

Dear Norman,

Thanks for your prompt reply and helpful information. According to the threads you provide, it seems that Starterware USB library intends to be a working library instead of being a high performance one. If this guess is true, then I can understand since in embedded system performance is normally highly hardware-dependent. I'll try the suggestions in those threads. Thanks again! :)

Regards,

Oliver

Dear Norman,

It's just like a magic: the transfer speed increased from 127 KB/s to 1,869 KB/s! Here is what I've done:

1. Increase both of the DATA_IN_EP_FIFO_SIZE & DATA_OUT_EP_FIFO_SIZE in usbdcdc.c from 64 Byte to 512 Byte

2. Locate all program and data to L2 

Since it's not practical to reserve all the precious L2 memory to USB function, I think I've to enable DMA to transfer data. In the thread you mentioned:

   http://e2e.ti.com/support/embedded/starterware/f/790/t/316923.aspx

there is a line enabling USB DMA:

  USBEndpointDMAEnable(USB0_BASE,USB_EP_1,USB_EP_DEV_OUT);

However, in my code simply calling this function with appropriate (I think) arguments will not work: PC fails to enumerate my USB device. I'm wondering if you happen to know where I can find any information about how to enable the USB DMA feature in Starterware?

Regards,

Oliver

Good to hear. I've always wondered if increasing the packet size would actually work. I guess the USB packet overhead is quite significant.

It has been a while, I vaguely remember that StarterWare uses DMA only in the Mass Storage example. Passing different arguments or enabling flags is not sufficient to enable DMA. The StarterWare USB driver is generic enough. There is DMA speciifc code is also in the USB Class portion as well. The DMA code is surrounded with #ifdef DMA_CODE. Look for that when porting. All other examples do not use DMA. I did eventually port the DMA changes from the Mass Storage to the Bulk Example. DMA uses a huge amount of memory (will not fit in L2 or L3) and I could not see any performance improvement. I might have done the port incorrectly. Others on this forum have also ported the DMA code. Search around. They might have had better luck.

Another thing to try is the interval attribute on the endpoint descriptor. You might be able to get the Host to poll your Device at a higher rate.

Dear Norman,

Thanks to your advice, I've found those files including DMA_MODE in Starterware's USB library. And, unfortunately, decreasing the interval from 10 to 1 doesn't improve performance. So, maybe I got to find some other way.

Anyway, thanks for your advice again! :)

Regards,

Oliver