I look for a way to set the weak pull-up resistor on a HPS pin (UART0_RX) to 'on' from the bootloader, before Linux boot and before an FPGA configuration is loaded to the device.
The general question would be, if it is even possible. The more detailed question of course would be: how?
I something like this
which talkes about exactly what I'm trying to do, but when I try to perform the described steps. nothing happens. I don't even get a file called iocsr_config_cyclone5.c from which I suppose is the file that could contain some pin assignments...
Any help much appreciated.
You can use Quartus prime pin planner, select the pull-up settings you need to apply for that UART, compile Quartus, this will generate the handoff files with the new applied pull-up. After that boot the system, uboot will configure the FPGA and apply all the pins settings before linux boots.