1. 我用的是STM32L151C8T6 的芯片，在github 上找了个别人的例程，拿来当模板改，由于他用的是HSE 外部晶振，我用的是内部晶振HSI，所以需要改系统时钟，改完后debug， 一直进不了main 函数，老以为是我改系统时钟改错了, 搞半天才找到原因，是printf 和微库 Use MicroLIB 的问题，keil 里面勾选就可以了
2. 改写系统初始化函数 void SetSysClock(void)， 关闭HSE， 使用HSI
void SetSysClock(void)
{__IO uint32_t StartUpCounter = 0;__IO uint32_t HSEStatus = 0;__IO uint32_t HSIStartUpCounter = 0;__IO uint32_t HSIStatus = 0;/* SYSCLK, HCLK, PCLK2 and PCLK1 configuration ---------------------------*/
// RCC->CR |= ((uint32_t)RCC_CR_HSEON); // Enable HSE
// /* Wait till HSE is ready and if Time out is reached exit */do
// {
// HSEStatus = RCC->CR & RCC_CR_HSERDY;
// StartUpCounter++;
// } while ((HSEStatus == 0) && (StartUpCounter != HSE_STARTUP_TIMEOUT));
// if ((RCC->CR & RCC_CR_HSERDY) != RESET)
// {
// HSEStatus = (uint32_t)0x01;
// }
// else
// {
// HSEStatus = (uint32_t)0x00;
// }
// if (HSEStatus == (uint32_t)0x01)
// {
// FLASH->ACR |= FLASH_ACR_ACC64; // Enable 64-bit access
// FLASH->ACR |= FLASH_ACR_PRFTEN; // Enable Prefetch Buffer
// FLASH->ACR |= FLASH_ACR_LATENCY; // Flash 1 wait state
// RCC->APB1ENR |= RCC_APB1ENR_PWREN; // Power enable
// PWR->CR = PWR_CR_VOS_0; // Select the Voltage Range 1 (1.8 V)
// while((PWR->CSR & PWR_CSR_VOSF) != RESET) // Wait Until the Voltage Regulator is ready
// {
// }
// RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1; // HCLK = SYSCLK /1
// RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE2_DIV1; // PCLK2 = HCLK /1
// RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE1_DIV1; // PCLK1 = HCLK /1
// /* PLL configuration */
// RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLMUL | RCC_CFGR_PLLDIV));
// RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSE | RCC_CFGR_PLLMUL12 | RCC_CFGR_PLLDIV3);
// RCC->CR |= RCC_CR_PLLON; // Enable PLL
// while((RCC->CR & RCC_CR_PLLRDY) == 0) // Wait till PLL is ready
// {
// }
// /* Select PLL as system clock source */
// RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
// RCC->CFGR |= (uint32_t)RCC_CFGR_SW_PLL;
// while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)RCC_CFGR_SWS_PLL) // Wait till PLL is used as system clock source
// {
// }
// }
// else // HSE startup fail, then use HSI as system clock source
// {RCC->CR |= RCC_CR_HSION; // enable HSI as system clock sourcedo{HSIStatus = RCC->CR & RCC_CR_HSIRDY;HSIStartUpCounter++;} while ((HSIStatus == 0) && (HSIStartUpCounter != HSI_STARTUP_TIMEOUT)); // Wait till HSI is ready and if Time out is reached exitif ((RCC->CR & RCC_CR_HSIRDY) != RESET){HSIStatus = (uint32_t)0x01;}else{HSIStatus = (uint32_t)0x00;}if (HSIStatus == (uint32_t)0x01){FLASH->ACR |= FLASH_ACR_ACC64; // Enable 64-bit accessFLASH->ACR |= FLASH_ACR_PRFTEN; // Enable Prefetch BufferFLASH->ACR |= FLASH_ACR_LATENCY; // Flash 1 wait stateRCC->APB1ENR |= RCC_APB1ENR_PWREN; // Power enablePWR->CR = PWR_CR_VOS_0; // Select the Voltage Range 1 (1.8 V)while((PWR->CSR & PWR_CSR_VOSF) != RESET) // Wait Until the Voltage Regulator is ready{}RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1; // HCLK = SYSCLK /1RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE2_DIV1; // PCLK2 = HCLK /1RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE1_DIV1; // PCLK1 = HCLK /1/* PLL configuration */RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLMUL | RCC_CFGR_PLLDIV));RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSI | RCC_CFGR_PLLMUL4 | RCC_CFGR_PLLDIV2);RCC->CR |= RCC_CR_PLLON; // Enable PLLwhile((RCC->CR & RCC_CR_PLLRDY) == 0) // Wait till PLL is ready{}/* Select PLL as system clock source */RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));RCC->CFGR |= (uint32_t)RCC_CFGR_SW_PLL;while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)RCC_CFGR_SWS_PLL) // Wait till PLL is used as system clock source{}}else{// HSI startup fail}
// }
}
3. STM32L151C8T6 系统时钟树，在STM32CubeMX 软件里面可以看的到
4. Debug 的时候一直卡在这个地方
5. 勾选微库，重新编译，再debug调试就OK了
6. 或者不勾选微库也行，禁用半主机模式就可以了
7. 跟fputc 没关系的， 重新编译，调试就可以了，查看系统各个总线的时钟
8. 我的问题是这个宏没有打开，导致下面的代码都没有编译进来，也就没有禁用半主机模式，没注意看他还在这里加了一个日志宏开关，我直接把他干掉了，坑爹的玩意
9. 启动文件，系统宏配置
