Anyone figured out how to do this? I’ve got a microUSB plugging into the EXT. board’s USB-UART (note: not the USB-UART for the keyboard) but cannot seem to pull up any output. Here’s what I’ve tried so far:
1500000bps N/8/1 (i.e. 1.5 Mbps, no parity, 8/1 bits, no flow control) - this is what uboot’s dtb for clockworkpi-a06 and
/proc/cmdline indicate, as well as other rk3399 chips, but no dice
115200bps N/8/1 - this is what the kernel’s dtb for clockworkpi-a06 is set to for stdout (but is seemingly overridden at boot time with
Here’s what I see in dmesg/kmsg on my machine when trying to connect to the USB-UART (
$ sudo cat /proc/kmsg <6>[866758.924517] usb 3-4: new full-speed USB device number 10 using xhci_hcd <6>[866759.077542] usb 3-4: New USB device found, idVendor=1a86, idProduct=7523, bcdDevice= 2.64 <6>[866759.077552] usb 3-4: Product: USB Serial <6>[866759.080136] usb 3-4: ch341-uart converter now attached to ttyUSB0 <3>[866785.945056] usb 3-4: failed to send control message: -71
Bonus points if you know how to capture output from u-boot too, over UART.
Any of the Clockwork folks around to drop some UART debugging tips or others who have tried?