Hi,
Are you still having an issue with this example code? I imported the uartEcho example project to my workspace and it worked fine on my BeagleBone (not Black), therefore I can't precisely pinpoint what would be a root cause for what you experienced.
One detail that caught my eye was that it seems you tried to create a project from scratch (due to the two linker .CMD files) and tried to modify the AM3359.cmd to accommodate the example project. This would require more extensive work and I strongly suggest using the original uartEcho.cmd file of the original project and see if it works with your board.
One final note: we at the CCS forum do not directly support these software packages, as they are heavily tied to the device and therefore you may get much better insights from the experts at the device forum.
Regards,
Rafael