raspi2 with multiple CPU's #1

[Ken Dickey]

Greetings,

I am running a small program for raspi2 (from http://wiki.osdev.org/ARM_RaspberryPi_Tutorial_C).

This code writes "Hello World", but the output ir repeated 4 times.

My thought was that this is emulating a 4 cpu core system.

However, when I check the MPIDR registed for CPU number, it always returns 1.

I git cloned github.com/qemu/qemu.git, made & installed on Acer ARM CB5-311 under Crouton/ubuntu.

./qemu.sh
1111

Linux:armv7l: ~/Downloads/RaspiTest/BareBones >>> uname -a
Linux localhost 3.10.18 #1 SMP Mon Nov 13 16:34:10 PST 2017 armv7l armv7l armv7l GNU/Linux

Linux:armv7l: ~/Downloads/RaspiTest/BareBones >>> qemu-system-arm --version
QEMU emulator version 2.10.91 (v2.11.0-rc1-dirty)
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers

=====
static inline uint32_t read_mpdir(void)
{
  uint32_t id;

  asm volatile("mrc p15, 0, %[id], c0, c0, 0 @ read MIDR\n\t"
        : [id] "=r" (id));
  return id;
}
======
void kernel_main(uint32_t r0, uint32_t r1, uint32_t atags)
{
 // Declare as unused
 (void) r0;
 (void) r1;
 (void) atags;

 uint32_t cpu_id;

 cpu_id = read_mpdir() & 0x03;

 uart_putc( "01234"[cpu_id] ); /* output is "1111" */

 if (cpu_id == 0) { /* code never executes 8^( */ }

====== qemu.sh
qemu-system-arm -m 256 -M raspi2 -no-reboot -serial stdio -kernel myos.elf

Thanks much,
-KenD

[Ken Dickey (ken-dickey)]

NOT A BUG

Reviewed the code and found the problem.

asm volatile("mrc p15, 0, %[id], c0, c0, 0 @ read MIDR\n\t" ...

I miscopied the code above; MIDR should have been MIPDR ( 5 )

I now get:

Linux:armv7l: ~/Downloads/RaspiTest/BareBones >>> ./qemu.sh
0H312ello, kernel World!

Sorry about the bogus report!
-KenD

[Ken Dickey (ken-dickey)]

Sorry again, "MPIDR"

Gotta learn to type!