Try using the attached binary files for this.
The same flow is used for both "Boot from UART" and "Debug prompt". The flow should be as follows:
- Hold the board in reset.
- Start sending the appropriate file (either debug or boot) as plain binary (no Xmodem or any other protocol)
- Immediately release the reset (so as to execute the BootROM while the pattern is still being transmitted).
- Wait for BootROM prompt (if debug file used) or for NACK signals (if boot file used) and if you terminal shows these NACKs.
- If you are doing boot. Start sending the UBoot with Xmodem.
I suggest to start with the debug prompt first, since you have a visual indication.
I am using the attached files and I can successful do both debug and boot. It is a matter of timing...
If you don't succeed in this try to enlarge the size of the pattern file, this will enhance the BootROM chance to catch the pattern...
I hope this helps.