USB issue on Atmel AT91SAM7X-EK boards
Posted by Dave Harper
on July 2, 2009
I just stumbled across a problem using the FreeRTOS USB task (from the lwIP_Demo_Rowley_ARM7 demo) on the AT91SAM7X-EK board and thought I would share it with anyone else in a similar situation.
I have been using this board to get familiar with FreeRTOS, lwIP and a number of other things before I design a custom board for my final application. I had previously completed an Eclipse project that had an AT45DB642D task (this is the dataflash on the AT91SAM7X-EK board). The task performed a series of tests on the dataflash and displayed the results on a web browser using lwIP. The next step in the roadmap was to add USB as this will be a great way to initially configure my custom board. Using the above demo as a guide, I added the USB to my new project but it didn't work. I finally tracked the problem down to the USB-CDC.c code which manipulates PA16. The comments in the code indicated that this controlled the USB pullup resistor, but looking at the schematics for the AT91SAM7X-EK showed that PA16 was used for SPI0_MISO which is connected to the dataflash device. It appears that the AT91SAM7X-EK doesn't have the ability to control the pullup resistor as this is an integral part of the STMicroelectronics USBUF02W6 part. I commented out all of the PA16 related lines in the code and everything started working. Wondering how this could have happened, I decided to take a look at the Atmel AT91SAM7S-EK schematics (the version of the board WITHOUT Ethernet). Sure enough, this board doesn't have dataflash but it does have the ability to control the USB pullup with - you guessed it - PA16.
The latest versions of board.h from the Atmel at91lib distribution check for a #define of the chip type to pull in the appropriate *.h chip definition file. This definition could also be used within the USB-CDC.c code to either enable or ignore the use of PA16.
RE: USB issue on Atmel AT91SAM7X-EK boards
Posted by Richard
on July 3, 2009
Thanks for the feedback. You are right of course, the 'x' board is a bit of a pain when developing USB because of its inability to turn in on an off. Note that the drivers in the demo are just that, a demo, and not intended to be a fully compliant example.
Copyright (C) 2004-2010 Richard Barry. Copyright (C) 2010-2016 Real Time Engineers Ltd.
Any and all data, files, source code, html content and documentation included in the FreeRTOSTM distribution or available on this site are the exclusive property of Real Time Engineers Ltd..
See the files license.txt (included in the distribution) and this copyright notice for more information. FreeRTOSTM and FreeRTOS.orgTM are trade marks of Real Time Engineers Ltd.