Agilex 5 premium board - es version - boots with gibberish prompts

Hello,

Few things come to mind that are worth investigating. The fact that U-Boot SPL output looks clean but the subsequent stages go garbled is a strong hint that something changes at that handoff point; most likely the UART baud rate being re-initialized differently, or a flow control mismatch that only surfaces once the next stage takes over. Could also be something in the PuTTY config itself that happens to be compatible with how SPL sets things up but not with what comes after.

Before anything else, it's worth double-checking your PuTTY serial settings and making sure flow control is explicitly set to None; PuTTY defaults to XON/XOFF and that alone can corrupt output on boards that don't use it. Also confirm you're on the right COM port; the Agilex 5 premium board's USB-UART adapter typically shows up as two COM ports on Windows and you want the lower-numbered one.

To help narrow this down further, could you share the following?

• Does the terminal show the same behavior every time you run? Like clean text outputs then garbled?
• Your exact PuTTY serial settings: baud rate, data bits, stop bits, parity, and especially flow control ( a snapshot would be good to have).
• Which COM port you're connected to and how many show up in Device Manager when the board is plugged in.
• How many gibberish transitions you see? is it one clean-to-garbled switch, or does it happen more than once across the boot sequence?
• Another suggestion worth trying: If you can catch the U-Boot prompt (spam a key during SPL to interrupt autoboot), run printenv baudrate and printenv bootargs and send the output; that would tell us about what the later stages are expecting.

Thank you,

Fawaz.