1 *.S文件分析
1.1 文件位置
启动文件为：freertos_GD32VF103/nuclei_sdk/SoC/gd32vf103/Common/Source/GCC/startup_gd32vf103.S
1.2 中断异常背景知识
GD32VF103的中断控制器具有两种模式：默认模式和ECLIC模式。模式的设置由mtvec[5:0]指定，当mtvec[5:0]==6’b000011时为ECLIC模式。处理函数入口由mtvec[31:6]指定（处理函数入口地址必须为64字节对齐）。
默认模式：所有中断，异常，NMI都由mtvec[31:6]指定的处理函数进行处理；
ECLIC模式：异常，NMI由mtvec[31:6]指定的处理函数进行处理，中断由mtvt2寄存器指定的处理函数进行处理，并由mtvt寄存器指定中断向量表地址
RISC-V处理器的中断系统和NVIC的中断系统不同，RISC-V的中断系统分为NMI，异常，外部中断三个概念。因此也分由不同的向量寄存器设置入口地址。由于risc-v的中断和异常都不进行自动现场保护，所以需要软件手动进行现场保护处理，因此无法直接使用C函数响应中断，需要一个基于汇编的入口函数进行处理，在汇编入口函数中再对C函数进行调用。
GD32VF103在ECLIC中断模式中，mtvec用于保存NMI和异常入口函数地址，不会进行自动的向量表调用。需要由入口函数进行转发处理。在官方代码中，响应函数为entry.S中的trap_entry函数。
mtvt2用于保存中断响应入口函数地址，处理函数位于entry.S中的irq_entry，函数mtvt保存向量表地址，mtvt2寄存器的irq_entry函数和mtvt寄存器中的向量表共同组成一个two-stage的中断向量表系统，irq_entry中对现场进行保护，并触发ECLIC调用中断向量表。
GD32VF103 ECLIC的中断向量寄存器
| 寄存器 | 全名 | 说明 |
|---|---|---|
| mtvec | Machine Trap-Vector Base-Address Register | 用于配置中断和异常处理程序的入口地址。一般用于处理NMI和异常中断 |
| mtvt | ECLIC Interrupt Vector Table Base Address | 用于保存ECLIC中断向量表的基地址，此基地址至少为64byte对齐。 |
| mtvt2 | ECLIC non-vectored interrupt handler address register | 用于指定ECLIC非向量模式的中断common-code入口地址。 |
2 源码分析
/*
* Copyright (c) 2019 Nuclei Limited. All rights reserved.
*
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the License); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an AS IS BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/******************************************************************************
* \file startup_gd32vf103.S
* \brief NMSIS Nuclei N/NX Class Core based Core Device Startup File for
* Device gd32vf103
* \version V1.00
* \date 21 Nov 2019
*
*
******************************************************************************/
#include "riscv_encoding.h"
.macro DECLARE_INT_HANDLER INT_HDL_NAME
#if defined(__riscv_xlen) && (__riscv_xlen == 32)
.word \INT_HDL_NAME
#else
.dword \INT_HDL_NAME
#endif
.endm
/*
* Put the interrupt vectors in this section according to the run mode:
* FlashXIP: .vtable
* ILM: .vtable
* Flash: .vtable_ilm
*/
//中断处理函数定义
#if defined(DOWNLOAD_MODE) && (DOWNLOAD_MODE == DOWNLOAD_MODE_FLASH)
.section .vtable_ilm
#else
.section .vtable
#endif
.weak eclic_msip_handler
.weak eclic_mtip_handler
.weak eclic_bwei_handler
.weak eclic_pmovi_handler
.weak WWDGT_IRQHandler
.weak LVD_IRQHandler
.weak TAMPER_IRQHandler
.weak RTC_IRQHandler
.weak FMC_IRQHandler
.weak RCU_IRQHandler
.weak EXTI0_IRQHandler
.weak EXTI1_IRQHandler
.weak EXTI2_IRQHandler
.weak EXTI3_IRQHandler
.weak EXTI4_IRQHandler
.weak DMA0_Channel0_IRQHandler
.weak DMA0_Channel1_IRQHandler
.weak DMA0_Channel2_IRQHandler
.weak DMA0_Channel3_IRQHandler
.weak DMA0_Channel4_IRQHandler
.weak DMA0_Channel5_IRQHandler
.weak DMA0_Channel6_IRQHandler
.weak ADC0_1_IRQHandler
.weak CAN0_TX_IRQHandler
.weak CAN0_RX0_IRQHandler
.weak CAN0_RX1_IRQHandler
.weak CAN0_EWMC_IRQHandler
.weak EXTI5_9_IRQHandler
.weak TIMER0_BRK_IRQHandler
.weak TIMER0_UP_IRQHandler
.weak TIMER0_TRG_CMT_IRQHandler
.weak TIMER0_Channel_IRQHandler
.weak TIMER1_IRQHandler
.weak TIMER2_IRQHandler
.weak TIMER3_IRQHandler
.weak I2C0_EV_IRQHandler
.weak I2C0_ER_IRQHandler
.weak I2C1_EV_IRQHandler
.weak I2C1_ER_IRQHandler
.weak SPI0_IRQHandler
.weak SPI1_IRQHandler
.weak USART0_IRQHandler
.weak USART1_IRQHandler
.weak USART2_IRQHandler
.weak EXTI10_15_IRQHandler
.weak RTC_Alarm_IRQHandler
.weak USBFS_WKUP_IRQHandler
.weak EXMC_IRQHandler
.weak TIMER4_IRQHandler
.weak SPI2_IRQHandler
.weak UART3_IRQHandler
.weak UART4_IRQHandler
.weak TIMER5_IRQHandler
.weak TIMER6_IRQHandler
.weak DMA1_Channel0_IRQHandler
.weak DMA1_Channel1_IRQHandler
.weak DMA1_Channel2_IRQHandler
.weak DMA1_Channel3_IRQHandler
.weak DMA1_Channel4_IRQHandler
.weak CAN1_TX_IRQHandler
.weak CAN1_RX0_IRQHandler
.weak CAN1_RX1_IRQHandler
.weak CAN1_EWMC_IRQHandler
.weak USBFS_IRQHandler
//中断向量表定义中断向量表vector_base被放置在.init段的首部从flash地址0x08000000开始。
//GD32VF103的中断向量表实际是由ECLIC控制器CSR寄存器中的mtvec、mtvt、mtvt2寄存器指定
//GD32VF103的中断控制器具有两种模式：默认模式和ECLIC模式。模式的设置由mtvec[5:0]指定，
//当mtvec[5:0]==6’b000011时为ECLIC模式。处理函数入口由mtvec[31:6]指定（处理函数入口地址必须为64字节对齐）。
//默认模式：所有中断，异常，NMI都由mtvec[31:6]指定的处理函数进行处理；
//ECLIC模式：异常，NMI由mtvec[31:6]指定的处理函数进行处理，中断由mtvt2寄存器指定的处理函数进行处理，并由mtvt寄存器指定中断向量表地址
.globl vector_base
vector_base:
#if defined(DOWNLOAD_MODE) && (DOWNLOAD_MODE != DOWNLOAD_MODE_FLASH)
j _start /* 0: Reserved, Jump to _start when reset for ILM/FlashXIP mode.*/
.align LOG_REGBYTES /* Need to align 4 byte for RV32, 8 Byte for RV64 */
#else
DECLARE_INT_HANDLER default_intexc_handler /* 0: Reserved, default handler for Flash download mode */
#endif
DECLARE_INT_HANDLER default_intexc_handler /* 1: Reserved */
DECLARE_INT_HANDLER default_intexc_handler /* 2: Reserved */
DECLARE_INT_HANDLER eclic_msip_handler /* 3: Machine software interrupt */
DECLARE_INT_HANDLER default_intexc_handler /* 4: Reserved */
DECLARE_INT_HANDLER default_intexc_handler /* 5: Reserved */
DECLARE_INT_HANDLER default_intexc_handler /* 6: Reserved */
DECLARE_INT_HANDLER eclic_mtip_handler /* 7: Machine timer interrupt */
DECLARE_INT_HANDLER default_intexc_handler /* 8: Reserved */
DECLARE_INT_HANDLER default_intexc_handler /* 9: Reserved */
DECLARE_INT_HANDLER default_intexc_handler /* 10: Reserved */
DECLARE_INT_HANDLER default_intexc_handler /* 11: Reserved */
DECLARE_INT_HANDLER default_intexc_handler /* 12: Reserved */
DECLARE_INT_HANDLER default_intexc_handler /* 13: Reserved */
DECLARE_INT_HANDLER default_intexc_handler /* 14: Reserved */
DECLARE_INT_HANDLER default_intexc_handler /* 15: Reserved */
DECLARE_INT_HANDLER default_intexc_handler /* 16: Reserved */
DECLARE_INT_HANDLER eclic_bwei_handler /* 17: Bus Error interrupt */
DECLARE_INT_HANDLER eclic_pmovi_handler /* 18: Performance Monitor */
DECLARE_INT_HANDLER WWDGT_IRQHandler
DECLARE_INT_HANDLER LVD_IRQHandler
DECLARE_INT_HANDLER TAMPER_IRQHandler
DECLARE_INT_HANDLER RTC_IRQHandler
DECLARE_INT_HANDLER FMC_IRQHandler
DECLARE_INT_HANDLER RCU_IRQHandler
DECLARE_INT_HANDLER EXTI0_IRQHandler
DECLARE_INT_HANDLER EXTI1_IRQHandler
DECLARE_INT_HANDLER EXTI2_IRQHandler
DECLARE_INT_HANDLER EXTI3_IRQHandler
DECLARE_INT_HANDLER EXTI4_IRQHandler
DECLARE_INT_HANDLER DMA0_Channel0_IRQHandler
DECLARE_INT_HANDLER DMA0_Channel1_IRQHandler
DECLARE_INT_HANDLER DMA0_Channel2_IRQHandler
DECLARE_INT_HANDLER DMA0_Channel3_IRQHandler
DECLARE_INT_HANDLER DMA0_Channel4_IRQHandler
DECLARE_INT_HANDLER DMA0_Channel5_IRQHandler
DECLARE_INT_HANDLER DMA0_Channel6_IRQHandler
DECLARE_INT_HANDLER ADC0_1_IRQHandler
DECLARE_INT_HANDLER CAN0_TX_IRQHandler
DECLARE_INT_HANDLER CAN0_RX0_IRQHandler
DECLARE_INT_HANDLER CAN0_RX1_IRQHandler
DECLARE_INT_HANDLER CAN0_EWMC_IRQHandler
DECLARE_INT_HANDLER EXTI5_9_IRQHandler
DECLARE_INT_HANDLER TIMER0_BRK_IRQHandler
DECLARE_INT_HANDLER TIMER0_UP_IRQHandler
DECLARE_INT_HANDLER TIMER0_TRG_CMT_IRQHandler
DECLARE_INT_HANDLER TIMER0_Channel_IRQHandler
DECLARE_INT_HANDLER TIMER1_IRQHandler
DECLARE_INT_HANDLER TIMER2_IRQHandler
DECLARE_INT_HANDLER TIMER3_IRQHandler
DECLARE_INT_HANDLER I2C0_EV_IRQHandler
DECLARE_INT_HANDLER I2C0_ER_IRQHandler
DECLARE_INT_HANDLER I2C1_EV_IRQHandler
DECLARE_INT_HANDLER I2C1_ER_IRQHandler
DECLARE_INT_HANDLER SPI0_IRQHandler
DECLARE_INT_HANDLER SPI1_IRQHandler
DECLARE_INT_HANDLER USART0_IRQHandler
DECLARE_INT_HANDLER USART1_IRQHandler
DECLARE_INT_HANDLER USART2_IRQHandler
DECLARE_INT_HANDLER EXTI10_15_IRQHandler
DECLARE_INT_HANDLER RTC_Alarm_IRQHandler
DECLARE_INT_HANDLER USBFS_WKUP_IRQHandler
DECLARE_INT_HANDLER default_intexc_handler
DECLARE_INT_HANDLER default_intexc_handler
DECLARE_INT_HANDLER default_intexc_handler
DECLARE_INT_HANDLER default_intexc_handler
DECLARE_INT_HANDLER default_intexc_handler
DECLARE_INT_HANDLER EXMC_IRQHandler
DECLARE_INT_HANDLER default_intexc_handler
DECLARE_INT_HANDLER TIMER4_IRQHandler
DECLARE_INT_HANDLER SPI2_IRQHandler
DECLARE_INT_HANDLER UART3_IRQHandler
DECLARE_INT_HANDLER UART4_IRQHandler
DECLARE_INT_HANDLER TIMER5_IRQHandler
DECLARE_INT_HANDLER TIMER6_IRQHandler
DECLARE_INT_HANDLER DMA1_Channel0_IRQHandler
DECLARE_INT_HANDLER DMA1_Channel1_IRQHandler
DECLARE_INT_HANDLER DMA1_Channel2_IRQHandler
DECLARE_INT_HANDLER DMA1_Channel3_IRQHandler
DECLARE_INT_HANDLER DMA1_Channel4_IRQHandler
DECLARE_INT_HANDLER default_intexc_handler
DECLARE_INT_HANDLER default_intexc_handler
DECLARE_INT_HANDLER CAN1_TX_IRQHandler
DECLARE_INT_HANDLER CAN1_RX0_IRQHandler
DECLARE_INT_HANDLER CAN1_RX1_IRQHandler
DECLARE_INT_HANDLER CAN1_EWMC_IRQHandler
DECLARE_INT_HANDLER USBFS_IRQHandler
.section .init //指明此处section名为.init
.globl _start //指明标签_start的属性为全局性
.type _start,@function
/**
* Reset Handler called on controller reset
*/
_start:
/* ===== Startup Stage 1 ===== */
/* Disable Global Interrupt */
// 关闭所有中断
csrc CSR_MSTATUS, MSTATUS_MIE
/* Jump to logical address first to ensure correct operation of RAM region */
//把_start地址载入到a0，根据启动位置的不同，_start可能在ram地址中也可能在flash中
la a0, _start
li a1, 1
// a1 = a1 << 29 (a1=0x20000000，ram起始地址)
slli a1, a1, 29
//if (a1 <= a0) goto _start0800检测是否在ram中运行，如果在ram中运行，_start地址将会大于 0x20000000
bleu a1, a0, _start0800
//a1 = a1 >> 2 （a1=0x08000000 flash起始地址)
srli a1, a1, 2
//if (a1 <= a0) goto _start0800
bleu a1, a0, _start0800
//a0 =_start0800 程序地址不正确
la a0, _start0800
//a0 = a0+0x08000000 (把程序地址重新定位到flash中)
add a0, a0, a1
//跳转到a0所存的地址
jr a0
_start0800:
/* Initialize GP and Stack Pointer SP */
.option push //保存编译设置
.option norelax //禁用相对寻址
//设置全局变量指针
la gp, __global_pointer$ //将标签__global_pointer$所处的地址赋值给gp寄存器
//标签__global_pointer$在链接脚本中定义，见链接脚本__global_pointer$标签
.option pop
//设置堆栈指针
la sp, _sp //将标签_sp所处的地址赋值给sp寄存器
//标签_sp在链接脚本中定义，见链接脚本_sp$标签
/*
* Set the the NMI base mnvec to share
* with mtvec by setting CSR_MMISC_CTL
* bit 9 NMI_CAUSE_FFF to 1
*/
//mmisc_ctl = 0x200 ECLIC寄存器mmisc_ctl用于控制NMI中断向量表，这里设置成和mtvec一致
li t0, MMISC_CTL_NMI_CAUSE_FFF
csrs CSR_MMISC_CTL, t0
/*
* Intialize ECLIC vector interrupt
* base address mtvt to vector_base
*/
//保存ECLIC中断向量表的基地址，mtvt保存向量表地址
la t0, vector_base
csrw CSR_MTVT, t0
/*
* Set ECLIC non-vector entry to be controlled
* by mtvt2 CSR register.
* Intialize ECLIC non-vector interrupt
* base address mtvt2 to irq_entry.
*/
//mtvt2用于保存中断响应入口函数地址
la t0, irq_entry
csrw CSR_MTVT2, t0
csrs CSR_MTVT2, 0x1
/*
* Set Exception Entry MTVEC to exc_entry
* Due to settings above, Exception and NMI
* will share common entry.
*/
//RISCV处理器在程序执行过程中，一旦遇到异常或者中断，则终止当前程序流，处理器被强行跳转到一
//个新的PC地址，该地址由mtvec寄存器指定。设置mtvec寄存器的值，使其指向异常处理函数入口
//mtvec用于保存NMI和异常入口函数地址
la t0, exc_entry
csrw CSR_MTVEC, t0
/* Set the interrupt processing mode to ECLIC mode */
//将中断处理模式设置为ECLIC模式，默认模式和ECLIC模式。模式的设置由mtvec[5:0]指定
li t0, 0x3f
csrc CSR_MTVEC, t0
csrs CSR_MTVEC, 0x3
/* ===== Startup Stage 2 ===== */
#ifdef __riscv_flen
/* Enable FPU */
li t0, MSTATUS_FS
csrs mstatus, t0
csrw fcsr, x0
#endif
/* Enable mcycle and minstret counter */
csrci CSR_MCOUNTINHIBIT, 0x5
//下列代码判断_ilm_lma和_ilm标签的地址是否相同
//如果相同，则意味着代码直接从Flash中执行，那么直接跳转到后面数字标签2所在的代码执行
//如果不相同，则意味着代码需要从Flash中上载至_ilm中执行，因此lw指令逐条将指令从Flash中读取出来，然后使用sw指令
//逐条写入_ilm中，通过此方式完成将指令上载至_ilm中
/* ===== Startup Stage 3 ===== */
/*
* Load code section from FLASH to ILM
* when code LMA is different with VMA
*/
la a0, _ilm_lma //将标签_ilm_lma所处的地址赋值给a0寄存器
//标签_ilm_lma在链接脚本中定义，见链接脚本_ilm_lma标签
la a1, _ilm //将标签_ilm所处的地址赋值给a1寄存器
//标签_ilm在链接脚本中定义，见链接脚本_ilm标签
/* If the ILM phy-address same as the logic-address, then quit */
beq a0, a1, 2f //a0和a1的值分别为标签_ilm_lma和_ilm标签的地址，判断其是否相等，如果相等
//则直接跳转到后面数字标签2所在的位置
la a2, _eilm //将_eilm所处我地址赋值给a2寄存器
//标签_eilm在链接脚本中定义，见链接脚本_eilm标签
//通过一个循环，将指令从Flash中搬到ITCM中
bgeu a1, a2, 2f//如果_ilm标签地址比_eilm标签地址还大，属于不正常的配置
//如果放弃搬运，直接跳转到后面数字标签2所在的位置
1:
/* Load code section if necessary */
lw t0, (a0) //从地址指针a0所在的位置（Flash中）读取32位数
sw t0, (a1) //将读取的32位数写入地址指针a1所在的位置（_ilm中）
addi a0, a0, 4 //将地址指针a0寄存器加4（即32位）
addi a1, a1, 4 //将地址指针a1寄存器加4（即32位）
bltu a1, a2, 1b //跳回之前数字标签1所在的位置
2:
/* Load data section */
//使用与上述相同的原理，通过一个循环，将数据从FLASH中搬运到DTCM中
la a0, _data_lma
la a1, _data
la a2, _edata
bgeu a1, a2, 2f
1:
lw t0, (a0)
sw t0, (a1)
addi a0, a0, 4
addi a1, a1, 4
bltu a1, a2, 1b
2:
/* Clear bss section */
//BSS段是链接器预留的未初始化变量所处的地址段，引导程序必须对其初始化为0
//此处通过一个循环来初始化BSS段
la a0, __bss_start
la a1, _end
bgeu a0, a1, 2f
1:
sw zero, (a0)
addi a0, a0, 4
bltu a0, a1, 1b
2:
/*
* Call vendor defined SystemInit to
* initialize the micro-controller system
*/
//系统初始化，主要是时钟初始化
call SystemInit
/* Call global constructors */
la a0, __libc_fini_array //将标签__libc_fini_array的值赋值给a0作为函数参数
call atexit //调用atexit函数
/* Call C/C++ constructor start up code */
call __libc_init_array //调用__libc_init_array
//上述 __libc_fini_array、atexit和__libc_init_array函数都是Newlib C运行库的特殊库函数，用于处理一些C/C++程序中
//的全局性的构造和析构函数。
//__libc_init_array函数会调用一个名为_init的函数
/* do pre-init steps before main */
call _premain_init
/* ===== Call Main Function ===== */
/* argc = argv = 0 */
//函数调用时由a0和a1寄存器传递参数
li a0, 0
li a1, 0
#ifdef RTOS_RTTHREAD
// Call entry function when using RT-Thread
call entry //调用entry函数，开始执行entry函数
#else
call main //调用main函数，开始执行main函数
#endif
/* do post-main steps after main */
call _postmain_fini
1:
j 1b //最后死循环，程序理论上不可能执行到此处
(1)__libc_init_array函数会调用一个名为_init的函数，该函数位于：freertos_GD32VF103/nuclei_sdk/SoC/gd32vf103/Common/Source/system_gd32vf103.c
_init函数源码：
void _init(void)
{
/* Don't put any code here, please use _premain_init now */
//该函数已经不在使用，使用_premain_init()函数
}
（2）由上述源码可知，_init函数已经不在使用，使用_premain_init()函数，_premain_init()函数源码：
void _premain_init(void)
{
/* TODO: Add your own initialization code here, called before main */
//用来计算当前运行频率
SystemCoreClock = get_cpu_freq();
/* configure USART */
//调用gd_com_init()函数对UART模块进行设计，串口打印信息就是要对uart进行初始化
gd_com_init(SOC_DEBUG_UART);
/* Display banner after UART initialized */
//UART初始化以后打印相关信息，有兴趣的可以进入函数看看打印了哪些内容
SystemBannerPrint();
/* Initialize exception default handlers */
//初始化异常处理程序
Exception_Init();
/* ECLIC initialization, mainly MTH and NLBIT */
//ECLIC初始化，主要是MTH和NLBIT
ECLIC_Init();
}
（2-1）get_cpu_freq()函数源码
uint32_t get_cpu_freq()
{
uint32_t cpu_freq;
// warm up
measure_cpu_freq(1);
// measure for real
//调用measure_cpu_freq()函数
cpu_freq = measure_cpu_freq(100);
return cpu_freq;
}
调用measure_cpu_freq()函数，measure_cpu_freq()函数源码：
uint32_t measure_cpu_freq(uint32_t n)
{
uint32_t start_mcycle, delta_mcycle;
uint32_t start_mtime, delta_mtime;
uint32_t mtime_freq = get_timer_freq();
// Don't start measuruing until we see an mtime tick
uint32_t tmp = (uint32_t)SysTimer_GetLoadValue();
do {
start_mtime = (uint32_t)SysTimer_GetLoadValue();
start_mcycle = __RV_CSR_READ(CSR_MCYCLE); //通过读取CSR寄存器MCYCLE得到当前时钟周期，并作为初始计数值
} while (start_mtime == tmp); //不断观察MTIME计数器并将其值作为初始化时间值
do {
delta_mtime = (uint32_t)SysTimer_GetLoadValue() - start_mtime;
//通过读取CSR寄存器MCYCLE得到当前时钟周期，并与初始计数值相减得到这段时间消耗的时钟周期
delta_mcycle = __RV_CSR_READ(CSR_MCYCLE) - start_mcycle;
} while (delta_mtime < n);
//MTIME计数器的频率是常开域的参考频率，Core的运行频率与CSR寄存器MCYCLE的值一致
//通过MCYCLE和MTIME的相对关系计算出当前Core的时钟频率
return (delta_mcycle / delta_mtime) * mtime_freq
+ ((delta_mcycle % delta_mtime) * mtime_freq) / delta_mtime;
}
（3）调用gd_com_init()函数对UART模块进行设计，串口打印信息就是要对uart进行初始化，有兴趣的同学可以自行查看
（4） SystemBannerPrint()，UART初始化以后打印相关信息，有兴趣的可以进入函数看看打印了哪些内容 ;
（5）Exception_Init()，初始化异常处理程序
（6）ECLIC_Init()，ECLIC初始化，主要是MTH和NLBIT
3 中断异常
3.1文件位置
中断异常文件：freertos_GD32VF103/nuclei_sdk/SoC/gd32vf103/Common/Source/GCC/intexc_gd32vf103.S
3.2源码分析
/*
* Copyright (c) 2019 Nuclei Limited. All rights reserved.
*
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the License); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an AS IS BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/******************************************************************************
* \file intexc_gd32vf103.S
* \brief NMSIS Interrupt and Exception Handling Template File
* for Device gd32vf103
* \version V1.00
* \date 7 Jan 2020
*
******************************************************************************/
#include "riscv_encoding.h"
/**
* \brief Global interrupt disabled
* \details
* This function disable global interrupt.
* \remarks
* - All the interrupt requests will be ignored by CPU.
*/
.macro DISABLE_MIE
csrc CSR_MSTATUS, MSTATUS_MIE
.endm
/**
* \brief Macro for context save
* \details
* This macro save ABI defined caller saved registers in the stack.
* \remarks
* - This Macro could use to save context when you enter to interrupt
* or exception
*/
/* Save caller registers */
.macro SAVE_CONTEXT
/* Allocate stack space for context saving */
//根据宏定义更改堆栈指针，分配20个单字（40位）或者14个单字（28位）空间用于保存寄存器
#ifndef __riscv_32e
addi sp, sp, -20*REGBYTES
#else
addi sp, sp, -14*REGBYTES
#endif /* __riscv_32e */
//保存ABI定义的“调用者应存储的寄存器（Caller saved register）”进入堆栈
STORE x1, 0*REGBYTES(sp)
STORE x4, 1*REGBYTES(sp)
STORE x5, 2*REGBYTES(sp)
STORE x6, 3*REGBYTES(sp)
STORE x7, 4*REGBYTES(sp)
STORE x10, 5*REGBYTES(sp)
STORE x11, 6*REGBYTES(sp)
STORE x12, 7*REGBYTES(sp)
STORE x13, 8*REGBYTES(sp)
STORE x14, 9*REGBYTES(sp)
STORE x15, 10*REGBYTES(sp)
#ifndef __riscv_32e
STORE x16, 14*REGBYTES(sp)
STORE x17, 15*REGBYTES(sp)
STORE x28, 16*REGBYTES(sp)
STORE x29, 17*REGBYTES(sp)
STORE x30, 18*REGBYTES(sp)
STORE x31, 19*REGBYTES(sp)
#endif /* __riscv_32e */
.endm
/**
* \brief Macro for restore caller registers
* \details
* This macro restore ABI defined caller saved registers from stack.
* \remarks
* - You could use this macro to restore context before you want return
* from interrupt or exeception
*/
/* Restore caller registers */
//回复用于从堆栈中恢复ABI定义的“调用者应存储的寄存器（Caller saved register）”
.macro RESTORE_CONTEXT
LOAD x1, 0*REGBYTES(sp)
LOAD x4, 1*REGBYTES(sp)
LOAD x5, 2*REGBYTES(sp)
LOAD x6, 3*REGBYTES(sp)
LOAD x7, 4*REGBYTES(sp)
LOAD x10, 5*REGBYTES(sp)
LOAD x11, 6*REGBYTES(sp)
LOAD x12, 7*REGBYTES(sp)
LOAD x13, 8*REGBYTES(sp)
LOAD x14, 9*REGBYTES(sp)
LOAD x15, 10*REGBYTES(sp)
#ifndef __riscv_32e
LOAD x16, 14*REGBYTES(sp)
LOAD x17, 15*REGBYTES(sp)
LOAD x28, 16*REGBYTES(sp)
LOAD x29, 17*REGBYTES(sp)
LOAD x30, 18*REGBYTES(sp)
LOAD x31, 19*REGBYTES(sp)
//恢复寄存器后，更改堆栈指针，回收20个单字（40位）或者14个单字（28位）空间
/* De-allocate the stack space */
addi sp, sp, 20*REGBYTES
#else
/* De-allocate the stack space */
addi sp, sp, 14*REGBYTES
#endif /* __riscv_32e */
.endm
/**
* \brief Macro for save necessary CSRs to stack
* \details
* This macro store MCAUSE, MEPC, MSUBM to stack.
*/
//将MCAUSE, MEPC, MSUBM寄存器里面的值存入到栈中
.macro SAVE_CSR_CONTEXT
/* Store CSR mcause to stack using pushmcause */
csrrwi x0, CSR_PUSHMCAUSE, 11
/* Store CSR mepc to stack using pushmepc */
csrrwi x0, CSR_PUSHMEPC, 12
/* Store CSR msub to stack using pushmsub */
csrrwi x0, CSR_PUSHMSUBM, 13
.endm
/**
* \brief Macro for restore necessary CSRs from stack
* \details
* This macro restore MSUBM, MEPC, MCAUSE from stack.
*/
//将MCAUSE, MEPC, MSUBM寄存器的值从栈中恢复
.macro RESTORE_CSR_CONTEXT
LOAD x5, 13*REGBYTES(sp)
csrw CSR_MSUBM, x5
LOAD x5, 12*REGBYTES(sp)
csrw CSR_MEPC, x5
LOAD x5, 11*REGBYTES(sp)
csrw CSR_MCAUSE, x5
.endm
/**
* \brief Exception/NMI Entry
* \details
* This function provide common entry functions for exception/nmi.
* \remarks
* This function provide a default exception/nmi entry.
* ABI defined caller save register and some CSR registers
* to be saved before enter interrupt handler and be restored before return.
*/
.section .text.trap
/* In CLIC mode, the exeception entry must be 64bytes aligned */
.align 6
.global exc_entry
//此处exc_entry标签为“弱（weak）属性”，“弱（weak）属性”为C/C++语法中定义的一种属性，一旦有具体的“非弱”性质同名函数存在/将会覆盖此函数
.weak exc_entry
exc_entry:
//保存相应的状态寄存器
/* Save the caller saving registers (context) */
SAVE_CONTEXT
/* Save the necessary CSR registers */
SAVE_CSR_CONTEXT
/*
* Set the exception handler function arguments
* argument 1: mcause value
* argument 2: current stack point(SP) value
*/
//传参，将mcause value和栈指针作为参数传给core_exception_handler()函数
csrr a0, mcause
mv a1, sp
/*
* TODO: Call the exception handler function
* By default, the function template is provided in
* system_Device.c, you can adjust it as you want
*/
//调用core_exception_handler()函数
call core_exception_handler
//恢复相应的状态寄存器
/* Restore the necessary CSR registers */
RESTORE_CSR_CONTEXT
/* Restore the caller saving registers (context) */
RESTORE_CONTEXT
/* Return to regular code */
//调用从异常模式返回
mret
/**
* \brief Non-Vector Interrupt Entry
* \details
* This function provide common entry functions for handling
* non-vector interrupts
* \remarks
* This function provide a default non-vector interrupt entry.
* ABI defined caller save register and some CSR registers need
* to be saved before enter interrupt handler and be restored before return.
*/
.section .text.irq
/* In CLIC mode, the interrupt entry must be 4bytes aligned */
.align 2
.global irq_entry
//此处irq_entry标签为“弱（weak）属性”，“弱（weak）属性”为C/C++语法中定义的一种属性，一旦有具体的“非弱”性质同名函数存在
//将会覆盖此函数
.weak irq_entry
/* This label will be set to MTVT2 register */
irq_entry:
保存相应的状态寄存器
/* Save the caller saving registers (context) */
SAVE_CONTEXT
/* Save the necessary CSR registers */
SAVE_CSR_CONTEXT
/* This special CSR read/write operation, which is actually
* claim the CLIC to find its pending highest ID, if the ID
* is not 0, then automatically enable the mstatus.MIE, and
* jump to its vector-entry-label, and update the link register
*/
//跳到中断向量表进行中断处理
csrrw ra, CSR_JALMNXTI, ra
/* Critical section with interrupts disabled */
//禁止所有中断
DISABLE_MIE
//恢复相应的状态寄存器
/* Restore the necessary CSR registers */
RESTORE_CSR_CONTEXT
/* Restore the caller saving registers (context) */
RESTORE_CONTEXT
/* Return to regular code */
//调用从中断模式返回
mret
/* Default Handler for Exceptions / Interrupts */
.global default_intexc_handler
.weak default_intexc_handler
Undef_Handler:
default_intexc_handler:
1: //数字标签
j 1b //跳转回标签1处，因此会成为死循环
