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#include <stdio.h>
#include <stm32l476xx.h>
int fputc(int ch, FILE *fp)
{
if (fp == &__stdout)
{
if (ch == '\n')
{
while ((USART2->ISR & USART_ISR_TXE) == 0);
USART2->TDR = '\r';
}
while ((USART2->ISR & USART_ISR_TXE) == 0);
USART2->TDR = ch;
}
return ch;
}
int main(void)
{
uint8_t flag = 0;
RCC->APB1ENR1 |= RCC_APB1ENR1_PWREN;
PWR->CR1 |= PWR_CR1_DBP; // 允许访问备用区域寄存器
// 打开LSE
if ((RCC->BDCR & RCC_BDCR_LSEON) == 0)
{
RCC->BDCR |= RCC_BDCR_LSEON;
while ((RCC->BDCR & RCC_BDCR_LSERDY) == 0); // 等待LSE稳定
flag = 1;
}
RCC->CR = (RCC->CR & ~RCC_CR_MSIRANGE) | RCC_CR_MSIRANGE_7 | RCC_CR_MSIRGSEL // MSI选8MHz时钟
| RCC_CR_MSIPLLEN; // 且使用LSE校准MSI
// 配置PLL: MSI/M*N/R=8MHz/1*18/2=72MHz
RCC->PLLCFGR = RCC_PLLCFGR_PLLREN | RCC_PLLCFGR_PLLN_4 | RCC_PLLCFGR_PLLN_1 | RCC_PLLCFGR_PLLSRC_MSI;
RCC->CR |= RCC_CR_PLLON;
while ((RCC->CR & RCC_CR_PLLRDY) == 0); // 等待PLL稳定
// 根据参考手册3.3.3 Read access latency, Table 11. Number of wait states according to CPU clock (HCLK) frequency
// CPU时钟要达到64MHz以上, LATENCY必须为4WS
// 由PWR_CR1_VOS可知当前V_CORE为Range 1 (最高时钟频率80MHz)
FLASH->ACR |= FLASH_ACR_LATENCY_4WS; // 参阅: Increasing the CPU frequency
while ((FLASH->ACR & FLASH_ACR_LATENCY) != FLASH_ACR_LATENCY_4WS);
// 将PLL选作系统时钟
RCC->CFGR |= RCC_CFGR_SW;
while ((RCC->CFGR & RCC_CFGR_SWS) != RCC_CFGR_SWS);
// LED灯配置
RCC->AHB2ENR = RCC_AHB2ENR_GPIOAEN;
GPIOA->MODER &= ~GPIO_MODER_MODE5_1;
GPIOA->BSRR = GPIO_BSRR_BS5; // LED灯亮
// 配置串口2
RCC->APB1ENR1 |= RCC_APB1ENR1_USART2EN;
GPIOA->MODER &= ~(GPIO_MODER_MODE2_0 | GPIO_MODER_MODE3_0 | GPIO_MODER_MODE9_0 | GPIO_MODER_MODE10_0);
GPIOA->AFR[0] = GPIO_AFRL_AFSEL2_2 | GPIO_AFRL_AFSEL2_1 | GPIO_AFRL_AFSEL2_0;
GPIOA->AFR[0] |= GPIO_AFRL_AFSEL3_2 | GPIO_AFRL_AFSEL3_1 | GPIO_AFRL_AFSEL3_0;
USART2->BRR = 72000000 / 115200; // 被除数为时钟频率, 除数为波特率
USART2->CR1 = USART_CR1_UE | USART_CR1_TE;
// 需要延时一会儿才能使用USART2, 否则会乱码
// 使用定时器2延时
RCC->APB1ENR1 |= RCC_APB1ENR1_TIM2EN;
//TIM2->ARR = 9999; // 10kHz/10000=1Hz -> 1s
TIM2->ARR = 9; // 10kHz/10=1kHz -> 1ms
TIM2->PSC = 7199; // 72MHz/7200=10kHz
TIM2->CR1 = TIM_CR1_OPM | TIM_CR1_URS;
TIM2->EGR = TIM_EGR_UG;
TIM2->CR1 |= TIM_CR1_CEN;
while ((TIM2->SR & TIM_SR_UIF) == 0);
printf("It works!!!\n");
if (flag)
printf("LSE has been connected!\n"); // 只有上电时才会显示这句话
printf("PWR->CR1=0x%08x\n", PWR->CR1);
printf("RCC->BDCR=0x%08x\n", RCC->BDCR);
printf("RCC->CFGR=0x%08x\n", RCC->CFGR);
printf("RCC->CR=0x%08x\n", RCC->CR);
printf("RCC->PLLCFGR=0x%08x\n", RCC->PLLCFGR);
printf("USART2->BRR=%d\n", USART2->BRR);
GPIOA->BRR = GPIO_BRR_BR5; // LED灯灭
while (1);
}
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