Bus Fault caused by write data to fds

RE: Bus Fault caused by write data to fds

Vidar Berg — Wed, 02 Jul 2025 06:02:58 GMT

Hi,

The blog explains how you can make the error precise by writing the DISDEFWBUF bit with GDB, but you can do the same from your code:

int main(void)
{
    /*
     *  "Make all memory stores precise at the cost of performance
     *   by setting DISDEFWBUF in the Cortex M3/M4 ACTLR reg" 
     *   (Ref. https://interrupt.memfault.com/blog/cortex-m-hardfault-debug#analysis-after-making-the-imprecise-error-precise) 
     */
    SCnSCB->ACTLR |= SCnSCB_ACTLR_DISDEFWBUF_Msk;
    
    ...

RE: Bus Fault caused by write data to fds

Chaoyue Ying — Wed, 02 Jul 2025 01:13:43 GMT

Hi,

I have finished reading all the relevant content in this blog.

It is mentioned that there is a trick we can use for the Cortex-M4 to make all memory stores precise.

I don't know what this technique refers to.Do you have any suggestions?

RE: Bus Fault caused by write data to fds

Vidar Berg — Tue, 01 Jul 2025 11:51:41 GMT

Hello,

I'm not familiar with the cmbacktrace tool, but the bfsr reg value (536916996) suggests that the "imprecise" bit is set. Please have a look at this blog post here https://interrupt.memfault.com/blog/cortex-m-hardfault-debug#imprecise-error-code-example which explains the meaning of this and what you can do to debug such faults.

Best regards,

Vidar