Bare metal, Assembly language • Accessing RP1 Peripherals from the BCM2712 on the Pi 5

I am attempting do some bare metal programming on the raspberry pi 5, and the lack of cohesive documentation has made it difficult.

Currently, as a "Hello World" of sorts, I am attempting to program UART0 on the board. I'm using the following documentation:

RP1 Peripherals
PL011 Documentation

The "RP1 Peripherals" document gives me the following table:



Am I correct in reading that the 40 bit System Addr column is for anything with direct bus access, and the Proc Addr is for the two Cortex M CPUs in the chip?

If so, what is the address space mapping for the BCM2712? For example, the UARTS have the following table:



Let's say I wanted to access UART0. I'm assuming the address given is a relative address.

So, assuming I haven't set up any page tables yet, my actual address will be:

UART_ACTUAL_ADDRESS = SOME_BASE_ADDRESS + 0x40030000

But what is the value of SOME_BASE_ADDRESS? I tried the 0x3F000000 used by the pi 4, and I'm not getting the expected post-reset values.

The first table indicates that 0xC000000000 might be correct for a full 64-bit address, but 0xC000000000 + 0x40030000 seems to give me dead memory.

I would appreciate some pointers here. I'm using the Debug probe + OpenOCD to load the images onto the board and debug, so I can step through the program and see exact values.

Statistics: Posted by tfinnegan937 — Tue Apr 02, 2024 12:12 am — Replies 7 — Views 76

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