Rock64 - Simple Bare-Metal Example
#1
Hi,

I wrote a simple Bare-Metal example for the Rock64.
It just sends a few strings over the UART interface and if a special char will be received, the program resets the Rock64.

The main entry point of the program (written in Assembler):

Code:
#include <asm.h>

IMPORT_C(kern_main)

.text

ENTRY(_start)
   mrs x0, SCTLR_EL1
   and x0, x0, #0xFFFFFFFFFFFFFFFC
   msr SCTLR_EL1, x0
   
   mrs x0, SCTLR_EL2
   and x0, x0, #0xFFFFFFFFFFFFFFFC
   msr SCTLR_EL2, x0
   
   mrs x0, MPIDR_EL1
   and x0, x0, #0x3
   cmp x0, #0
   beq L1
L0:
   wfe
   b L0
L1:
   ldr x0, =_kern_stack_s
   mov sp, x0
   b kern_main
L2:
   wfe
   b L2

.end

It's a minimal setup. It just disables the MMU and the Alignment checks.
Then it reads the processor ID and let only CPU0 run the C main entry point (kern_main).

The C main entry point:

Code:
#include <dev/cru.h>
#include <dev/uart.h>

void kern_main(void)
{
   int c;
   
   uart_init();
   uart_puts("Pine64 Rock64\r\n");
   uart_puts("Press 'r' to reset the board!\r\n");
   
   do {
       c = uart_getc();
   } while (c != 'r');
   
   uart_puts("Resetting...\r\n");
   cru_reset();
   
   while (1)
       ;
}

Should be self explaining.

There is also as very simple UART driver and the CRU driver for resetting the board.
The code includes a very minimal C String library.Only GCC for AArch64 is needed.

To start the application, U-Boot is needed.

I have attached the full code.
The code is also on my GitHub page available.

Edit:
Oops! There is a bug in the attached archive.

Simple change the following line in the file start.S...
Code:
ldr x0, =_kern_stack_s

to..
Code:
ldr x0, =_kern_stack_e


Attached Files
.gz   bare-metal.tar.gz (Size: 4.47 KB / Downloads: 14)
Code:
/* Beware of bugs in the above code; I have only proved it correct, not tried it */
 Original quote by Donald E. Knuth
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