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?