RISCV基础开发(十四)

gewenbin
gewenbin
gewenbin
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2021年8月21日13:41:26 评论 734

QEMU裸机开发之S模式软中断

S模式下的软中断我们借助m模式下的定时器中断进行触发,在m模式下设置sip中的soft位域就可以触发S模式下的软中断,如下所示。

void machine_trap(void)
{ 
    unsigned long cause = mcause_get();
    unsigned long mepc  = mepc_get();
    unsigned long tval  = mtval_get();

    int is_int = (cause & (1l << 63l)) ? 1 : 0;
    int mcode = cause & 0xff;

    if (mcode >= 16) {
        printf("%s : %s.\r\n", is_int ? "Interrupt" : "Exception", "Unknown code");
        return;
    }

    if (is_int) {
        printf("Interrupt : %s.\r\n", interrupt_cause[mcode]); 
        switch (mcode) {
        case M_SOFT_INT:
            msoftint_clear();
            break;
        case M_TIMER_INT:
            timer_set(timer_get() + TIMER_CLK_RATE);
            // raise a supervisor software interrupt.
            sip_set(SIP_SSIP);
            break;
        }
    } else {
        printf("Exception : %s.\r\n", exception_cause[mcode]); 
        switch (mcode) {
        case ILLEGAL_INSTRUCTION:
            printf("tval = %p\r\n", tval);
            printf("mepc = %p\r\n", mepc);
            break;
        case ECALL_FROM_SMODE:
            break;
        }

        mepc_set(mepc + 4);
    }

    return;
}

当m模式中断处理结束时就会立马进入s模式中断处理,在s模式的软中断处理中通过将sip中的soft位域置0来清除s模式软中断状态,如下所示。

void supervisor_trap(void)
{ 
    unsigned long tval = stval_get();
    unsigned long sepc = sepc_get();
    unsigned long cause = scause_get();

    int is_int = (cause & (1l << 63l)) ? 1 : 0;
    int scode = cause & 0xff;

    if (scode >= 16) {
        printf("%s : %s.\r\n", is_int ? "Interrupt" : "Exception", "Unknown code");
        return;
    }

    if (is_int) {
        printf("Interrupt : %s.\r\n", interrupt_cause[scode]); 
        switch (scode) {
        case S_SOFT_INT:
            // acknowledge the software interrupt by clearing
            // the SSIP bit in sip.
            sip_set(sip_get() & (~SIP_SSIP));
            break;
        case S_TIMER_INT:
            break;
        }
    } else {
        printf("Exception : %s.\r\n", exception_cause[scode]); 
        switch (scode) {
        case ILLEGAL_INSTRUCTION:
            printf("tval = %p\r\n", tval);
            printf("sepc = %p\r\n", sepc);
            break;
        }

        sepc_set(sepc + 4);
    }

    return;
}

在“start”中设置定时器以让定时器产生可以产生中断,如下所示。

void start(void)
{
    printf("%s %d.\r\n", __func__, __LINE__);

    machine_trap_init();

    //msoftint_make();
    timer_set(timer_get() + TIMER_CLK_RATE);

    machine_switchto_supervisor();
}

注意本章节只是为了说明S模式软中断是如何使用的而采用了一种简单方便的测试方法,在实际的软件中,需要借助OpenSBI来进行核间中断设置和处理。

在命令行执行“make qemu”,可以看到先打印m模式下定时器中断信息,然后再打印s模式下的软中断信息,如下所示。

gewenbin@gewenbin-virtual-machine:~/Desktop/qemu_test/lesson9$ make qemu
riscv64-unknown-elf-gcc    -c -o entry.o entry.S
riscv64-unknown-elf-gcc -Wall -Werror -O -fno-omit-frame-pointer -ggdb -mcmodel=medany -ffreestanding -fno-common -nostdlib -mno-relax -I. -fno-stack-protector -fno-pie -no-pie   -c -o start.o start.c
riscv64-unknown-elf-gcc -Wall -Werror -O -fno-omit-frame-pointer -ggdb -mcmodel=medany -ffreestanding -fno-common -nostdlib -mno-relax -I. -fno-stack-protector -fno-pie -no-pie   -c -o uart.o uart.c
riscv64-unknown-elf-gcc -Wall -Werror -O -fno-omit-frame-pointer -ggdb -mcmodel=medany -ffreestanding -fno-common -nostdlib -mno-relax -I. -fno-stack-protector -fno-pie -no-pie   -c -o trap.o trap.c
riscv64-unknown-elf-gcc -Wall -Werror -O -fno-omit-frame-pointer -ggdb -mcmodel=medany -ffreestanding -fno-common -nostdlib -mno-relax -I. -fno-stack-protector -fno-pie -no-pie   -c -o clint.o clint.c
riscv64-unknown-elf-ld -z max-page-size=4096 -T kernel.ld -o kernelimage entry.o start.o uart.o trap.o clint.o 
riscv64-unknown-elf-objdump -S kernelimage > kernel.asm
riscv64-unknown-elf-objdump -t kernelimage | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$/d' > kernel.sym
qemu-system-riscv64 -machine virt -bios none -kernel kernelimage -m 128M -smp 1 -nographic
start 76.
main 44.
Interrupt : Machine timer interrupt.
Interrupt : Supervisor software interrupt.
Interrupt : Machine timer interrupt.
Interrupt : Supervisor software interrupt.
Interrupt : Machine timer interrupt.
Interrupt : Supervisor software interrupt.

工程源码:链接:https://pan.baidu.com/s/1TnTYr7mywdKj5bxpdmWnyA,提取码:q772,见lesson9。

gewenbin
  • 本文由 发表于 2021年8月21日13:41:26
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