USB DMA issues on AM335x boards

USB DMA issues on AM335x boards
Technical Note
USB DMA issues on AM335x boards
The information in this document is relevant for all PHYTEC products populated with the
Texas Instruments AM335x microcontroller and running with kernel version 3.2.
PHYTEC AM335x boards running with kernel version 3.2 may show USB issues when DMA is
enabled.
The PHYTEC AM335x 3.2 kernel is based on the TI PSP 04.06.00.11 Release, which is also
included in the Sitara SDK 6.00.00. Thus a description of this issue can also be found on
the TI web side at:
http://processors.wiki.ti.com/index.php/Sitara_SDK_6.00.00_Release_Notes
"Devices which use the Mentor MUSB core currently disable the DMA due to instability issues.
This will cause degradation from the expected USB throughput performance. The DMA support
can be enabled in the kernel depending on your use case. The most commonly affected use
cases are when the USB core is being used in host mode and there is both DMA and PIO traffic
occurring at the same time. This has been observed with many USB WiFi adapters as well as
when doing I/O operations to one device which inserting or removing another device.
If you choose to enable DMA you should extensively test your use case to verify that no lockup
occurs."
We could reproduce this issue on different boards, using a USB HUB and connecting 2 USB
sticks. Reading and Writing on both sticks at the same time produced I/O errors.
This issue could not be reproduced when DMA is disabled.
Workaround :
We recommend to disable DMA or to at least test your use case extensively.
Disabling DMA in BSP:
1. Change into the BSP directory
2. Change kernel config like this:
ptxdist kernelconfig
Device Drivers --->
[*] USB support --->
[*] Disable DMA (always use PIO)
3. Exit and Save the kernelconfig
4. Rebuild the kernel with:
ptxdist targetinstall kernel
© PHYTEC Messtechnik GmbH 2014
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Technical Note
Please contact our support if you need any further information.
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ƒ +49 (6131) 9221-31
ƒ [email protected]
France:
ƒ +33 (0) 2 43 29 22 33
ƒ [email protected]
North America:
ƒ +1 (206) 780-9047, or
+1 (800) 278-9913
ƒ [email protected]
India:
ƒ +91 (80) 4130-7589
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ƒ [email protected]
© PHYTEC Messtechnik GmbH 2014
TN-040e_1
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