Hello,

Has anyone been able to squeeze out any extra serial ports on a Pi4? If so, what's the trick?

 I have /dev/ser3 working fine at address 0xfe201600 using IRQ 153. But I can't get any of the others that reside at 
addresses 0xfe201000, 0xfe201400, 0xfe201800, or 0xfe201a00. It seems they all want to share IRQ 153 but if I do this 
for any address other than 0xfe201600 the call to InterruptAttach() (in devc/serpl011/intr.c) results in the kernel gong
 into ga ga land and a subsequent reboot (presumably the watchdog kicks in).

Am I missing something? I feel like I'm so close after pouring over as many of the RPi4B docs that I can find.

Is it true that all the UART's need to attach to IRQ 153?

Thanks,

Geoff.