I'm working with a custom board that resembles the Zoom OMAP-L138 eXperimenter. I am trying to interface UART2 Tx and Rx pins from the SOM to a Spartan 3 FPGA. I am aware that UART2 is used for the Kernel console, but I disabled it. The FPGA and the SOM's pin are both LVCMOS 3.3v, so the connection is passive. I'm using the default "pull" configuration for the SOM and the FPGAs UART Rx pin is configured as a pull-up. When connected the voltage levels seem fine, but after debugging several events occurred:
1. After a few hours of debugging the SOM stopped booting (no bootloader messages). This occurred on two boards, so I suspect a problem with the interface board, but its a pretty simple design, since It passively connects the UART pins. I verified the data from the UART2 Tx pin.
2. I inserted a new SOM without the UART interface board and I received messages from the bootloaders, but the Linux kernel hangs. When I enable the Linux console to use the UART2 for the control, the last message is: Uncompressing Linux... done, booting the kernel.
3. I attempted to debug the Kernel using the XDS510USB JTAG and after connecting, Linux booted with no reported problems. I did rebuild the Kernel with debug info, but I checked if the Kernel booted before using JTAG.
4. I attempted to test the UART connection one last time, and now I can't even boot using JTAG (SOM seems to be fine). I'm currently trying to figure out where the Kernel is hanging.
When the Kernel booted after connecting JTAG, I was really confused... At this point I'm suspecting an issue with the SOM caused by the UART connection.
Any comments would be appreciated.