RISC-V MCU启动文件分析
启动文件由汇编语言编写，是MCU上电复位后第一个执行的程序。主要执行以下内容：
- 初始化gp(global pointer)全局指针寄存器、sp(stack pointer)栈指针寄存器
- 将data数据从flash中加载至RAM中
- 清空bss段数据
- 初始化中断向量表
- 配置系统时钟
- 从Machine模式切换到User模式，进入main函数运行
CH32V103启动文件如下：
1 /********************************** (C) COPYRIGHT ******************************* 2 * File Name : startup_ch32v10x.s 3 * Author : WCH 4 * Version : V1.0.0 5 * Date : 2020/04/30 6 * Description : CH32V10x vector table for eclipse toolchain. 7 *******************************************************************************/ 8 9 .section .init,"ax",@progbits /* 声明section 为 .init */ 10 .global _start /* 指明标签_start的属性为全局性的 */ 11 .align 1 12 _start: /* 标签_start处 */ 13 j handle_reset /* 跳转至 handle_reset处 */ 14 .word 0x00000013 /* 内核设计需要，不用关注 */ 15 .word 0x00000013 16 .word 0x00000013 17 .word 0x00000013 18 .word 0x00000013 19 .word 0x00000013 20 .word 0x00000013 21 .word 0x00000013 22 .word 0x00000013 23 .word 0x00000013 24 .word 0x00000013 25 .word 0x00000013 26 .word 0x00100073 27 .section .vector,"ax",@progbits 28 .align 1 29 _vector_base: /* 中断向量表 */ 30 .option norvc; 31 j _start 32 .word 0 33 j NMI_Handler /* NMI Handler */ 34 j HardFault_Handler /* Hard Fault Handler */ 35 .word 0 36 .word 0 37 .word 0 38 .word 0 39 .word 0 40 .word 0 41 .word 0 42 .word 0 43 j SysTick_Handler /* SysTick Handler */ 44 .word 0 45 j SW_handler /* SW Handler */ 46 .word 0 47 /* External Interrupts */ 48 j WWDG_IRQHandler /* Window Watchdog */ 49 j PVD_IRQHandler /* PVD through EXTI Line detect */ 50 j TAMPER_IRQHandler /* TAMPER */ 51 j RTC_IRQHandler /* RTC */ 52 j FLASH_IRQHandler /* Flash */ 53 j RCC_IRQHandler /* RCC */ 54 j EXTI0_IRQHandler /* EXTI Line 0 */ 55 j EXTI1_IRQHandler /* EXTI Line 1 */ 56 j EXTI2_IRQHandler /* EXTI Line 2 */ 57 j EXTI3_IRQHandler /* EXTI Line 3 */ 58 j EXTI4_IRQHandler /* EXTI Line 4 */ 59 j DMA1_Channel1_IRQHandler /* DMA1 Channel 1 */ 60 j DMA1_Channel2_IRQHandler /* DMA1 Channel 2 */ 61 j DMA1_Channel3_IRQHandler /* DMA1 Channel 3 */ 62 j DMA1_Channel4_IRQHandler /* DMA1 Channel 4 */ 63 j DMA1_Channel5_IRQHandler /* DMA1 Channel 5 */ 64 j DMA1_Channel6_IRQHandler /* DMA1 Channel 6 */ 65 j DMA1_Channel7_IRQHandler /* DMA1 Channel 7 */ 66 j ADC1_2_IRQHandler /* ADC1_2 */ 67 .word 0 68 .word 0 69 .word 0 70 .word 0 71 j EXTI9_5_IRQHandler /* EXTI Line 9..5 */ 72 j TIM1_BRK_IRQHandler /* TIM1 Break */ 73 j TIM1_UP_IRQHandler /* TIM1 Update */ 74 j TIM1_TRG_COM_IRQHandler /* TIM1 Trigger and Commutation */ 75 j TIM1_CC_IRQHandler /* TIM1 Capture Compare */ 76 j TIM2_IRQHandler /* TIM2 */ 77 j TIM3_IRQHandler /* TIM3 */ 78 j TIM4_IRQHandler /* TIM4 */ 79 j I2C1_EV_IRQHandler /* I2C1 Event */ 80 j I2C1_ER_IRQHandler /* I2C1 Error */ 81 j I2C2_EV_IRQHandler /* I2C2 Event */ 82 j I2C2_ER_IRQHandler /* I2C2 Error */ 83 j SPI1_IRQHandler /* SPI1 */ 84 j SPI2_IRQHandler /* SPI2 */ 85 j USART1_IRQHandler /* USART1 */ 86 j USART2_IRQHandler /* USART2 */ 87 j USART3_IRQHandler /* USART3 */ 88 j EXTI15_10_IRQHandler /* EXTI Line 15..10 */ 89 j RTCAlarm_IRQHandler /* RTC Alarm through EXTI Line */ 90 j USBWakeUp_IRQHandler /* USB Wakeup from suspend */ 91 j USBHD_IRQHandler /* USBHD */ 92 93 .option rvc; 94 95 .section .text. , "ax", @progbits /* 中断服务程序弱定义 */ 96 .weak NMI_Handler 97 .weak HardFault_Handler 98 .weak SysTick_Handler 99 .weak SW_handler 100 .weak WWDG_IRQHandler 101 .weak PVD_IRQHandler 102 .weak TAMPER_IRQHandler 103 .weak RTC_IRQHandler 104 .weak FLASH_IRQHandler 105 .weak RCC_IRQHandler 106 .weak EXTI0_IRQHandler 107 .weak EXTI1_IRQHandler 108 .weak EXTI2_IRQHandler 109 .weak EXTI3_IRQHandler 110 .weak EXTI4_IRQHandler 111 .weak DMA1_Channel1_IRQHandler 112 .weak DMA1_Channel2_IRQHandler 113 .weak DMA1_Channel3_IRQHandler 114 .weak DMA1_Channel4_IRQHandler 115 .weak DMA1_Channel5_IRQHandler 116 .weak DMA1_Channel6_IRQHandler 117 .weak DMA1_Channel7_IRQHandler 118 .weak ADC1_2_IRQHandler 119 .weak EXTI9_5_IRQHandler 120 .weak TIM1_BRK_IRQHandler 121 .weak TIM1_UP_IRQHandler 122 .weak TIM1_TRG_COM_IRQHandler 123 .weak TIM1_CC_IRQHandler 124 .weak TIM2_IRQHandler 125 .weak TIM3_IRQHandler 126 .weak TIM4_IRQHandler 127 .weak I2C1_EV_IRQHandler 128 .weak I2C1_ER_IRQHandler 129 .weak I2C2_EV_IRQHandler 130 .weak I2C2_ER_IRQHandler 131 .weak SPI1_IRQHandler 132 .weak SPI2_IRQHandler 133 .weak USART1_IRQHandler 134 .weak USART2_IRQHandler 135 .weak USART3_IRQHandler 136 .weak EXTI15_10_IRQHandler 137 .weak RTCAlarm_IRQHandler 138 .weak USBWakeUp_IRQHandler 139 .weak USBHD_IRQHandler 140 141 .section .text.handle_reset,"ax",@progbits 142 .weak handle_reset 143 .align 1 144 handle_reset: /* handle_reset起始位置 */ 145 .option push 146 .option norelax 147 la gp, __global_pointer$ /* 将ld文件中的标签__global_pointer所处的地址值赋给gp寄存器 */ 148 .option pop 149 1: 150 la sp, _eusrstack /* 将ld文件中的标签_eusrstack所处的地址值赋给sp寄存器 */ 151 2: 152 /* Load data section from flash to RAM */ 153 la a0, _data_lma 154 la a1, _data_vma 155 la a2, _edata 156 bgeu a1, a2, 2f 157 1: 158 lw t0, (a0) 159 sw t0, (a1) 160 addi a0, a0, 4 161 addi a1, a1, 4 162 bltu a1, a2, 1b 163 2: 164 /* clear bss section */ 165 la a0, _sbss 166 la a1, _ebss 167 bgeu a0, a1, 2f 168 1: 169 sw zero, (a0) 170 addi a0, a0, 4 171 bltu a0, a1, 1b 172 2: 173 /* enable all interrupt */ /* csrs ，根据寄存器中每个为1的位，把CSR寄存器对应位置位 */ 174 li t0, 0x88 175 csrs mstatus, t0 /* 状态寄存器mstatus赋值为0x88，打开所有中断，设置MPP值为00 */ 176 la t0, _vector_base 177 ori t0, t0, 1 178 csrw mtvec, t0 /* 将中断向量表的首地址赋值给mtvec寄存器（中断发生时PC的地址） */ 179 180 jal SystemInit /* 设置MCU系统时钟 */ 181 la t0, main 182 csrw mepc, t0 183 mret 184 185 /* 186 mret返回指令(M模式特有的指令)，调用该指令会进行如下操作： 187 188 - 将PC指针设置为mepc的值 189 - 将mstatus的MPIE域复制到MIE来恢复之前的中断使能 190 - 将权限模式设置为mstatus的MPP域中的值。 191 192 芯片上电默认进入的是机器模式，通过将mstatus中的MPP值设置为00（00: User, 01: Supervisor, 11: Machine）， 193 并将main函数的地址赋值给mepc，调用mret，使得用户在进入main函数运行时，芯片由机器模式切换为用户模式。 194 */
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