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raspi2 with multiple CPU's #1
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
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
Sorry again, "MPIDR"
Gotta learn to type!
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