[ Question ] UART FIFO Constant

[ldelossa]

Hey there,

I'm trying to write directly to UART on the riscv virt machine type in qemu.

I see you're usage here:
https://github.com/noteed/riscv-hello-asm/blob/main/hello.s#L28

I'm not familiar with the way the defined constant is wrapping the t0 register. What is this doing?

[noteed]

Hi, I'm not at all experienced in assembly, but my guess is that it defines t0 to be UART_BASE 5 lines above. Then at the line you highlighted, it defines t2 to be UART_REG_TXFIFO further than t0. A bit like array indexing, where t0 is the beginning of the array, and UART_REG_TXFIFO is its index.