On 04/05/2012 12:08, David Jander wrote:
Hi all,
Hi David,
I discovered a bug in u-boot, that got evident after Freescale updated the i.MX51 datasheets to revision 5 in March this year. I don't know if it is a serious problem or not, but if I believe the wording of the datasheet many of the boards that use a i.MX51 processor and running u-boot as of latest git, can potentially suffer "permanent damage", whatever that means.
I am referring to the new paragraphs at the end of chapter 4.3.4 of the datasheet, and the wrong interpretation of the meaning of the HVE bit in the iomuxc.h header file of u-boot here:
arch/arm/include/asm/arch-mx5/iomux.h:
... 69 PAD_CTL_DRV_VOT_LOW = 0x0 << 13, /* Low voltage mode */ 70 PAD_CTL_DRV_VOT_HIGH = 0x1 << 13,/* High voltage mode */ ...
Agree. The header defines the bit wrongly.
It seems to me that the Reference Manual is correct. It is from 24/2/2010 and it was not updated.
After a reset, value is set to 1, and this means low-voltage for the most pins.
According to the reference manual, the correct meaning of this bit is negated:
"Bit 13: High / Low Output Voltage Range. This bit selects the output voltage mode for SD2_CMD. 0 High output voltage mode 1 Low output voltage mode"
Added to the new paragraph in the datasheet:
"The UHVIO type of I/O cells have to be configured properly according to their supply voltage level, in order to prevent permanent damage to them and in order to not degrade their timing performance."
Seems like we may have a problem here!
I would like to know if anyone is aware of this? Does anyone know of a board that is actually destroyed this way?
At the moment, we have no problems and I can explain why. The only boards setting these pins (for SD card) are mx51evk and vision2. Both are setting PAD_CTL_DRV_VOT_HIGH, and because the define is wrong, they are really setting the pin to low output voltage mode.
For other boards and other pins, voltage is not explicitely set : this means they work in low voltage mode after a reset.
To fix arch/arm/include/asm/arch-mx5/iomux.h and synchronize it with the documentation, we need also to change mx51evk / vision2, setting the pins to PAD_CTL_DRV_VOT_LOW, and they will work as now.
We can also drop completely PAD_CTL_DRV_VOT_HIGH from these two boards and use the reset value.
Best regards, Stefano Babic