GPMC hardware contention with e-MMC

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Jan 7, 2015, 1:31:19 PM1/7/15
I want to use GPMC with the Bone-Black. For the best GPMC performance I want to use the address/data multiplexed mode: the pins AD0..AD15 will transmit the address and data, the pins A0..A11 transmit the remaining address bits. Looking at the BBB schematics page 3 there seems to be a possible contention on these pins. Could please someone with BBB hardware knowledge explain whether there is electrical contention on GPMC_AD[7:0], GPMC_A4, and GPMC_A9. 

1. There is the e-MMC hanging off AD0..AD7. The e-MMC can be put in reset, but according to the Micron data sheet p.5 the DAT[7:0] drivers are push-pull. The Micron data sheet does not say anything about high impedance. Therefore, even in reset these pins will be driven by the e-MMC chip. (At least this is how I understand the data sheet.)

2. After resetting the e-MMC, it defaults to using only DAT0. It means that even in reset this pin is driven by the e-MMC, conflicting with its GPMC use as an AD0 signal.

3. The e-MMC reset signal hangs off GPMC_A4 (ball R14). It means that I cannot use ball R14 for the GPMC address bit 4, because it is needed to hold the e-MMC in reset.

4. The GPMC_A9 is used as HDMI interrupt. So here again I cannot use this pin for GPMC.

So how can I use the GPMC in the multiplexed mode with AD[15:0], A[11:0]? Should I desolder the e-MMC from the board to avoid electrical contention on these pins?

Should I redirect the HDMI interrupt to some other GPIO pin by cutting the PCB trace and using a jumper wire?

Thank you,

Gerald Coley

Jan 8, 2015, 2:58:07 PM1/8/15
These are decisions you have to make. I mentioned this before as being an issue sharing both modes. Sounds like you finally came to the same conclusion. The chip was designed fro one or the other. Not both, despite the ability in SW to switch modes.

You need to remove the eMMC from the board. Cut an jumper as you wish.But you need to change the SW to make the interrupt work.


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Jan 8, 2015, 3:31:44 PM1/8/15
thank you for explanations. I am a newcomer to the Beagle. I was quite confused seeing frequent remarks that e-MMC can be held in reset in order to use the GPMC. Being neither a SW nor a HW person I tend to consult all such details with the respective data sheets before committing to copper. I just wanted to make sure that my understanding is correct before modifying the schematics.
Thank you -- Wojtek

Mark Lazarewicz

Jan 8, 2015, 5:41:07 PM1/8/15
The gpmc pins will also need to be reconfigured in SW

From: Gerald Coley <>
on with e-MMC
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