STM32 unaligned access | 易学教程

问题

Periodically, the program enters the HardFault_Handler. In the register HFSR set bit FORCED and in UFSR register set UNALIGNED. The project uses STM32F417, FreeRtos, LWIP. In most cases, the error in the stack are LWIP function. The error occurs rarely once a few days. The program is compiled with the flag --no_unaligned_access. It is unclear why there is such an error - while --no_unaligned_access flag is enabled and even every few days, and second whether it is possible to process or ignore this error and continue the program?

回答1:

(I know this is years after the OQ. Posting in case it's still helpful.)

I'm working on a project that is using LWIP 1.4.1 that does have at least one unaligned access fault; I've just now fixed it. (I'm here researching if this is a known issue.)

In src/netif/etharp.c: etharp_request()

  return etharp_raw(netif, (struct eth_addr *)netif->hwaddr, &ethbroadcast,
                (struct eth_addr *)netif->hwaddr, &netif->ip_addr, &ethzero,
                ipaddr, ARP_REQUEST);

The cast (struct eth_addr *)netif->hwaddr is causing the non-alignment of netif->hwaddr to be discarded. A subsquent memcpy() inside etharp_raw() then faults.

The solution I've shoe-horned in is to allocate temporary storage that is aligned and pass that instead:

  struct eth_addr hwaddr;
  memcpy(hwaddr.addr, netif->hwaddr, ETHARP_HWADDR_LEN);

  return etharp_raw(netif, &hwaddr, &ethbroadcast,
                &hwaddr, &netif->ip_addr, &ethzero,
                ipaddr, ARP_REQUEST);

A quick check through the rest of etharp.c reveals quite a number of such casts, some of which are harmless but at least one or two others are also likely to fault.

回答2:

lwIP 2.x has been released since mid-last year (2018). My experience is that changing over from 1.4x to 2.x did not cause any/much issues, so it's best to switch over. That sort of problems (if they are actual problems) might have been fixed.

Also, the F4x series is Cortex-M4, so they can do unaligned access. It would only cause problems if you are using F0xx or L0xx series that uses the Cortex-M0+ core.

回答3:

I don't know if this is already resolved. But I ran into same problem with (STM32F746) during one of the project. Here is one application note from IAR:

STM32 unaligned access

Solution: Just add

SCB->CCR = SCB->CCR & ~(1<<3);//Resetting the 3rd bit (meant for enabling hardfault for unaligned access)

Check if it is still relevant for you.

In my case I was using packed structures which was causing this problem. After above mentioned fix with option 1, it got away for me.

来源：https://stackoverflow.com/questions/41218915/stm32-unaligned-access

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arm

stm32