Register difference between emulator and silicone

[urish]

Reproduction instructions

To reproduce, load the following hex file into the emulator and silicone, and set a GDB breakpoint at the beginning of main (e.g. break main):

test-printf.zip

Run both in the emulator and on the silicone rp2040. Then print the register values, and you'll see r12 has a different value between the emulator and the silicone.

I'm not sure if this is actually a bug or just a symptom of a missing peripheral / peripheral implementation difference (e.g. timer), so we need to investigate.

Reproduction logs

Running on silicone:

(gdb) monitor reset init
target halted due to debug-request, current mode: Thread 
xPSR: 0xf1000000 pc: 0x000000ee msp: 0x20041f00
target halted due to debug-request, current mode: Thread
xPSR: 0xf1000000 pc: 0x000000ee msp: 0x20041f00
(gdb) break main
Breakpoint 1 at 0x10000342: file /home/uri/p/test-printf/test-printf.ino, line 2.
(gdb) c
Continuing.
Note: automatically using hardware breakpoints for read-only addresses.
target halted due to debug-request, current mode: Thread 
xPSR: 0x01000000 pc: 0x00000178 msp: 0x20041f00

Thread 1 hit Breakpoint 1, main () at /home/uri/p/test-printf/test-printf.ino:2
2         printf("12 is %d\n", 12);
(gdb) info registers
r0             0x0                 0
r1             0x10001cd9          268442841
r2             0x20002858          536881240
r3             0x1                 1
r4             0x0                 0
r5             0x0                 0
r6             0x0                 0
r7             0x0                 0
r8             0x0                 0
r9             0x0                 0
r10            0x0                 0
r11            0x0                 0
r12            0x5                 5
sp             0x2000ceb0          0x2000ceb0 <_main_stack+32744>
lr             0x100040a7          268452007
pc             0x10000342          0x10000342 <main()+2>
xPSR           0x61000000          1627389952
msp            0x2003ffb8          0x2003ffb8
psp            0x2000ceb0          0x2000ceb0 <_main_stack+32744>
primask        0x0                 0
basepri        0x0                 0
faultmask      0x0                 0
control        0x2                 2

Running in the emulator:

0x10000000 in ?? ()
A program is being debugged already.
Are you sure you want to change the file? (y or n) y
Reading symbols from test-printf.ino.elf...
(gdb) break main
Breakpoint 1 at 0x10000342: file /home/uri/p/test-printf/test-printf.ino, line 2.
(gdb) c
Continuing.

Breakpoint 1, main () at /home/uri/p/test-printf/test-printf.ino:2
2         printf("12 is %d\n", 12);
(gdb) info registers
r0             0x0                 0
r1             0x10001cd9          268442841
r2             0x20002858          536881240
r3             0x1                 1
r4             0x0                 0
r5             0x0                 0
r6             0x0                 0
r7             0x0                 0
r8             0x0                 0
r9             0x0                 0
r10            0x0                 0
r11            0x0                 0
r12            0xa                 10
sp             0x2000ceb0          0x2000ceb0 <_main_stack+32744>
lr             0x100040a7          268452007
pc             0x10000342          0x10000342 <main()+2>
xPSR           0x61000000          1627389952
msp            0x2003ffb8          0x2003ffb8
psp            0x2000ceb0          0x2000ceb0 <_main_stack+32744>
primask        0x0                 0
basepri        0x0                 0
faultmask      0x0                 0
control        0x2                 2
(gdb)

difference:

Silicone - r12 0x5 5
Emulator - r12 0xa 10