ChibiOS Free Embedded RTOS

Interestingly, if
#define CH_DBG_SYSTEM_STATE_CHECK TRUE
SV # 4 happens during initialization tasks "lwip_thread", and if
#define CH_DBG_SYSTEM_STATE_CHECK FALSE
see the situation described above (a few pings).
CH_DBG_SYSTEM_STATE_CHECK and CH_DBG_ENABLE_ASSERTS allows you to abort program flow ...

Looping won't help.

sdcStart(&SDCD1, NULL);
if( sdcConnect(SDCDriver *sdcp) == CH_SUCCESS ){
FRESULT res = f_mount(&SDC_FS, "0:", 1);
if(res == FR_OK ){
chprintf(chp, "mounted succesfully\n");
}else{
chprintf(chp, "mounting failed\n");
}
}else{
chprintf(chp, "sdcConnect failed\n");
}

What ...

I've looked into Chibios used here. (2.6)
But it seems you can only use the fatfs bindings with the SDCDriver, or the MMCDriver. Not Serial, not SPI.

Typically there is no pullup on the clk line. m (the transistor is optional, to be able to turn off the card)
Also, the EMI filters in the image ...

They are the docs of the cortex m4. However, the m0 is equal in he basics. The m4 has some more advanced instructions. I guess (do not know for sure) the interrupt model is equal.
You linked me to the "ARM-V7" port page. I have a cortex M0. People who already know such a thing think it is obvious ...

FATFS* fs;
f_getfree("0:", &freeClusters, &fs);

Works fine here. But, you'd need to call sdcStart, sdcConnect and f_mount (successfully) before f_getfree works.

You say you have an 8mb card, don't you mean 8 GB? If so, you're doing undefined stuff because the maximum size is 4 GB. Make sure ...

chSysLock -> port_lock ->
register uint32_t basepri __asm("basepri");
basepri = CORTEX_BASEPRI_KERNEL;

Does not explicitly disable all interrupts on STM32. It elevates the current interrupt priority mask to some level.
If compiled with CORTEX_SIMPLIFIED_PRIORITY it will be __disable_irq ...

Meanwhile, I can confirm writing and reading from an 8GB SanDisk SDHC card works*.
However, getting metadata doesn't. It won't read the filesize correctly anymore. It does with a FILINFO.
It seems after f_open, the fsize isn't being set correctly if the file is beyond 4 GB.

MSTACK is indeed the first piece or memory to be allocated to the beginning of the coupled memory.
Didn't thought of it that way.

Currently I've set it to 512 bytes. That would be enough to fit two interrupt routines, assuming they to not throw an exception.
I'll set it back to 4kB, which is ...

That makes sense.
But what is preventing interrupts from running out of stack?
Should the stack size fit all enabled interrupts?

Ah, I see it sets basepri to 0x20 in chSysLockFromIsr()...
And if I'm not mistaken this allows nested interrupts for the kernel and not the HAL.
Can I find a list of preemptable interrupts?

Usually I am not going this low level in arm.