AC6优化等级-OZ后,触发错误中断,错误原因:企图执行非对齐访问,如何解决?

发布于 2022-12-13 16:10:04 浏览：767 订阅该版

[tocm]

### 环境
- 硬件ART-PI STM32H750
- 编译器 KEIL AC6 -OZ
### 问题
- 进入错误中断,原因企图执行非对齐访问

![screenshot_image.png](https://oss-club.rt-thread.org/uploads/20221213/5c534a280232369f73dc7a843c97a9ff.png)

### 定位错误代码

- 执行如下汇编后进入错误中断

```ASM
LDM           r1!,{r2}
```

![screenshot_image.png](https://oss-club.rt-thread.org/uploads/20221213/17d82471f199d442328322c392a9c2b0.png)

- 执行如下程序,在断点处继续运行触发错误中断
```c
  /* Transmit data in 8 Bit mode */
  else
  {
    while (hspi->TxXferCount > 0UL)
    {
      /* Wait until TXP flag is set to send data */
      if (__HAL_SPI_GET_FLAG(hspi, SPI_FLAG_TXP))
      {
        if ((hspi->TxXferCount > 3UL) && (hspi->Init.FifoThreshold > SPI_FIFO_THRESHOLD_03DATA))
        {
		 //下面这句话发生错误
          *((__IO uint32_t *)&hspi->Instance->TXDR) = *((uint32_t *)hspi->pTxBuffPtr);
          hspi->pTxBuffPtr += sizeof(uint32_t);
          hspi->TxXferCount -= (uint16_t)4UL;
        }
        else if ((hspi->TxXferCount > 1UL) && (hspi->Init.FifoThreshold > SPI_FIFO_THRESHOLD_01DATA))
        {
#if defined (__GNUC__)
          *ptxdr_16bits = *((uint16_t *)hspi->pTxBuffPtr);
#else
          *((__IO uint16_t *)&hspi->Instance->TXDR) = *((uint16_t *)hspi->pTxBuffPtr);
#endif /* __GNUC__ */
          hspi->pTxBuffPtr += sizeof(uint16_t);
          hspi->TxXferCount -= (uint16_t)2UL;
        }
        else
        {
          *((__IO uint8_t *)&hspi->Instance->TXDR) = *((uint8_t *)hspi->pTxBuffPtr);
          hspi->pTxBuffPtr += sizeof(uint8_t);
          hspi->TxXferCount--;
        }
      }
```

### 疑问
- 我对汇编代码进行理解后发现汇编语句并没有问题
- 不知道是哪里错误导致的
- 下面这个是优化等级为-O0的汇编代码,这个可以正常运行

![screenshot_image.png](https://oss-club.rt-thread.org/uploads/20221213/bc603db4c20e8400bf6dda55a6e36b59.png)

- 优化等级-OS,可以运行

![screenshot_image.png](https://oss-club.rt-thread.org/uploads/20221213/64fc3af58a586e22c548c6cd9a91bd57.png)

### 对比-OZ 和 -OS汇编代码
- -OS汇编代码
```ASM
0x900091D6 6DE1      LDR           r1,[r4,#0x5C]
0x900091D8 F8512B04  LDR           r2,[r1],#0x04
0x900091DC 6202      STR           r2,[r0,#0x20]
0x900091DE F64F70FC  MOVW          r0,#0xFFFC
0x900091E2 E013      B             0x9000920C
```

- -Oz汇编代码
```ASM
0x90009012 6DE1      LDR           r1,[r4,#0x5C]
0x90009014 C904      LDM           r1!,{r2}
0x90009016 6202      STR           r2,[r0,#0x20]
0x90009018 F64F70FC  MOVW          r0,#0xFFFC
0x9000901C E013      B             0x90009046
```

- 区别仅在第二行
这运行有什么区别?
我汇编现学的,没看出运行有什么不同来

![screenshot_image.png](https://oss-club.rt-thread.org/uploads/20221213/76a7372730daf9e72d4a25acf0777f1a.png.webp)