本篇文章将从多个方面对ARM裸机开发进行详细阐述，包括硬件配置、编写启动代码、串口输出等。如果您还不了解裸机开发，我们会从简单的示例开始，逐步带您走入ARM裸机开发的世界。
一、硬件配置
在进行ARM裸机开发之前，我们需要了解所需的硬件组件和配置，以便正确进行开发。
首先，我们需要一片带有ARM内核的单片机。以STM32F103为例，需要将芯片的晶振设置为8MHz，并添加必要的外部电路，包括复位电路、串口模块等。以下是对于STM32F103的基本硬件配置示例代码：
#include "stm32f103xb.h"
void SystemInit(void)
{
/* Reset the RCC clock configuration to the default reset state */
RCC->CR |= RCC_CR_HSION; /* Enable HSI */
while ((RCC->CR & RCC_CR_HSIRDY) == 0); /* Wait for HSI Ready */
RCC->CFGR = 0x00000000U; /* Reset CFGR register */
RCC->CR &= ~(RCC_CR_HSEON | RCC_CR_CSSON | RCC_CR_PLLON);
RCC->CR &= ~(RCC_CR_HSEBYP);
RCC->CIR = 0x00000000U; /* Disable all interrupts */
/* Configure the System clock frequency, HCLK, PCLK2 and PCLK1 */
RCC->CFGR &= ~(RCC_CFGR_SW);
RCC->CFGR |= RCC_CFGR_SW_HSI; /* HSI is selected as System clock */
while ((RCC->CFGR & RCC_CFGR_SWS) != RCC_CFGR_SWS_HSI); /* Wait for System Clock switch */
}
二、编写启动代码
在进行ARM裸机开发时，我们需要编写启动代码来初始化处理器，并将其移到正常操作模式。以下示例代码演示了如何编写启动代码：
; Reset Handler Reset_Handler: ; Initialize stack pointer as first thing. LDR R0, =_estack MOV SP, R0 ; Copy data from ROM to RAM LDR R0, =_sdata ; R0 = start address of data in ROM LDR R1, =_sdata ; R1 = start address of data in RAM LDR R2, =_edata ; R2 = end address of data in RAM CopyDataLoop: CMP R1, R2 ; Have we copied all data? ADDLT R3, R0, R1 ; If not, copy the next word LDR R3, [R3] STRLT R3, [R1] ADDLT R1, R1, #4 ; Increment the pointers BLT CopyDataLoop ; And loop if not done. ; Clear the zero-initialized BSS section. LDR R0, =_sbss LDR R1, =_ebss MOV R2, #0 ClearBssLoop: CMP R0, R1 ; Have we cleared everything? STRLT R2, [R0] ; If not, clear the next word ADDLT R0, R0, #4 ; Increment the pointer BLT ClearBssLoop ; And loop if not done. ; Call main() LDR R0, =main BX R0 ; Define an empty stack area _estack: .word 0x20001000 ; Define the beginning and end of the data section. ; We link these to the ROM and RAM addresses being the same. _sdata = _stext _edata = _etext ; Define the beginning and end of the "zero initialized" ; section (which is just full of 0's in the ROM image). _sbss = _edata _ebss = _stack_top
三、串口输出
在ARM裸机开发中，我们经常需要使用串口输出进行调试。以下是使用UART1模块进行串口输出的示例代码：
#include "stm32f103xb.h"
void UART1_Init(void)
{
/* Enable USART1 and GPIOA clocks */
RCC->APB2ENR |= RCC_APB2ENR_USART1EN | RCC_APB2ENR_IOPAEN;
/* Configure PA9 and PA10 for USART1 */
GPIOA->CRH &= ~(GPIO_CRH_CNF9 | GPIO_CRH_MODE9 | GPIO_CRH_CNF10 | GPIO_CRH_MODE10);
GPIOA->CRH |= GPIO_CRH_CNF9_1 | GPIO_CRH_MODE9 | GPIO_CRH_MODE10;
/* Configure USART1 for 115200 baud, 8 data bits, no parity, 1 stop bit */
USART1->BRR = 0x1A1; /* 72MHz / 115200 = 625 */
USART1->CR1 = USART_CR1_TE | USART_CR1_RE | USART_CR1_UE;
}
void UART1_SendChar(char ch)
{
/* Wait for previous byte to be sent */
while ((USART1->SR & USART_SR_TXE) == 0);
/* Write byte to USART1 buffer */
USART1->DR = ch;
}
void UART1_SendString(const char *str)
{
while (*str != ' ')
{
UART1_SendChar(*str);
str++;
}
}
四、中断处理
在ARM裸机开发中，中断是非常重要的一环。以下示例代码演示了如何编写基于NVIC（Nested Vectored Interrupt Controller）的中断处理函数：
#include "stm32f103xb.h"
void USART1_IRQHandler(void)
{
if (USART1->SR & USART_SR_RXNE)
{
char ch = USART1->DR;
/* Do something with received byte */
}
}
int main(void)
{
/* Enable USART1 and GPIOA clocks */
RCC->APB2ENR |= RCC_APB2ENR_USART1EN | RCC_APB2ENR_IOPAEN;
/* Configure PA9 and PA10 for USART1 */
GPIOA->CRH &= ~(GPIO_CRH_CNF9 | GPIO_CRH_MODE9 | GPIO_CRH_CNF10 | GPIO_CRH_MODE10);
GPIOA->CRH |= GPIO_CRH_CNF9_1 | GPIO_CRH_MODE9 | GPIO_CRH_MODE10;
/* Configure USART1 for 115200 baud, 8 data bits, no parity, 1 stop bit */
USART1->BRR = 0x1A1; /* 72MHz / 115200 = 625 */
USART1->CR1 = USART_CR1_TE | USART_CR1_RE | USART_CR1_UE | USART_CR1_RXNEIE;
/* Enable USART1 interrupt */
NVIC_EnableIRQ(USART1_IRQn);
/* Loop forever, handling interrupts as they occur */
while (1)
{
}
}
五、总结
本文主要从硬件配置、编写启动代码、串口输出以及中断处理等方面对ARM裸机开发进行了详细阐述，并提供了相应的示例代码。如果您想深入了解ARM裸机开发，建议阅读更多相关文献，并通过实际的项目实践来提升自己的开发能力。