Host CPU load with QEMU ports

[yf13]

I am seeing high host CPU use from QEMU with idle REPL console on both VIRT_RV32 and MPS2_AN385 boards. My host is a PC running Ubuntu 22.04. Is this expected behavior?

[jonnor]

MicroPython is primarily for bare-metal, and there is no RTOS in the core. So probably it just spins as fast as the "CPU" can execute. Which will take up non-trivial amount of CPU on the host, when using an emulator.

[agatti]

The QEMU port will spin in ports/qemu/mphalport.c regardless of the architecture, in mp_hal_stdin_rx_chr to be precise.

If you want to lower CPU time, you may achieve that by rewriting the console's UART interaction to be interrupt driven - and I guess you'll then need to implement your own version of MICROPY_INTERNAL_WFE for both Arm and RV32 targets or the interpreter won't process timers/delayed events until there's an incoming keypress.

[yf13]

thank you both. Now I understand current behavior is expected due to hot spins in UART read.