在picorv32上面对 rt-thread nano的移植

发布于 2020-07-01 20:08:35 浏览：2480 订阅该版

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* 本帖最后由 Stupid_bird 于 2020-7-1 20:20 编辑 *

PicoRV32 是使用verilog实现一个简单的RISC-V CPU 
只需要很少的资源消耗便可以移植到FPGA中运行起来。
几个月之前忽然想尝试将RT-Thread 内核移植到 PicoRV32 CPU上运行起来的想法，于是有了目前这个帖子。
第一次写帖子如有问题望大家见谅 ，记录一下移植的方法 欢迎大家交流。
 PicoRV32  内核的github地址 ： [https://github.com/cliffordwolf/picorv32](https://github.com/cliffordwolf/picorv32)

目前情况 已经基本完成RT-Thread的移植工作。工程连接：[https://github.com/flyfishR/rtthread-nano](https://github.com/flyfishR/rtthread-nano)FPGA工程 ：https://gitee.com/Stupid_bird/picorv32_EG4S20.git
移植方法
1、使用的工具链是 gcc 在picorv32 GitHub上有安装方法
2、调试的时候使用的是modelsim （:L 好麻烦。。。。）移植主要需要实现下面几个函数 
1、启动代码 start.s
2、上下文切换函数 
      rt_hw_context_switch_to
      rt_hw_context_switch
      rt_hw_context_switch_interrupt
3、全局中断开关
      rt_hw_interrupt_disable
      rt_hw_interrupt_enable
4、中断管理函数
     rt_hw_interrupt_init
     rt_hw_interrupt_mask
     rt_hw_interrupt_umask
     rt_hw_interrupt_install

启动代码1、主要完成了CPU寄存器、数据段和BSS段的初始化工作 提供好C语言的运行环境
```_pvstart: 
/* zero-initialize all registers */
    addi x1, zero, 0
    addi x2, zero, 0
    addi x3, zero, 0
    addi x4, zero, 0
    addi x5, zero, 0
    addi x6, zero, 0
    addi x7, zero, 0
    addi x8, zero, 0
    addi x9, zero, 0
    addi x10, zero, 0
    addi x11, zero, 0
    addi x12, zero, 0
    addi x13, zero, 0
    addi x14, zero, 0
    addi x15, zero, 0
    addi x16, zero, 0
    addi x17, zero, 0
    addi x18, zero, 0
    addi x19, zero, 0
    addi x20, zero, 0
    addi x21, zero, 0
    addi x22, zero, 0
    addi x23, zero, 0
    addi x24, zero, 0
    addi x25, zero, 0
    addi x26, zero, 0
    addi x27, zero, 0
    addi x28, zero, 0
    addi x29, zero, 0
    addi x30, zero, 0
    addi x31, zero, 0

/* set stack pointer */

lui sp, %hi(_riscv_sp)
    addi sp, sp, %lo(_riscv_sp)

addi sp,sp,-16
    sw zero,0(sp)
    sw zero,4(sp)
    sw zero,8(sp)
    sw zero,12(sp)
//        picorv32_waitirq_insn(zero)
    picorv32_maskirq_insn(zero, zero)
    j _start
    ebreak

_start:
# Initialize global pointer
1:  auipc gp, %pcrel_hi(__global_pointer$)
    addi  gp, gp, %pcrel_lo(1b)
# Clear the bss segment
    la      a0, _edata
    la      a1, _end
_bss_init: 
    addi        a0,a0,4
    sw            zero,-4(a0)
    bgeu        a1,a0,_bss_init
  
# Init the data segment 
    la      a0, _data
    la      a1, _edata
    la      a2, _data_lma  
_data_init: 
    addi        a2,a2,4
    lw            a5,-4(a2)
    addi        a0,a0,4
    sw            a5,-4(a0)
    bgeu        a1,a0,_data_init
# call entry  
    li      a0, 0             
    call    entry
    ebreak

riscv_maskirq:
        picorv32_maskirq_insn(a0, a0)
        ret
riscv_timer:
        picorv32_timer_insn(a0, a0)
        ret
riscv_getirq:
        picorv32_getq_insn(a0, q1)
        ret

```

2、进程切换
 rt_hw_context_switch_interrupt
```void rt_hw_context_switch_interrupt(rt_ubase_t from, rt_ubase_t to)
{
    if (rt_thread_switch_interrupt_flag == 0)
        rt_interrupt_from_thread = from;

rt_interrupt_to_thread = to;
    rt_thread_switch_interrupt_flag = 1;

return ;
}``` rt_hw_context_switch 
这个函数要说明一下 我这边使用的触发中断的方式来实现进程切换的 使用的rt_thread_switch_interrupt_flag  这个变量来标记 是否要进入中断状态 ，实际进入中断是在 rt_hw_interrupt_enable函数中后面会看到实现方法。
```void rt_hw_context_switch(rt_ubase_t from, rt_ubase_t to)
{
    if (rt_thread_switch_interrupt_flag == 0)
        rt_interrupt_from_thread = from;

rt_interrupt_to_thread = to;
    rt_thread_switch_interrupt_flag = 1;
    rt_hw_context_switch_flag=1 ;
    return ;
}```rt_hw_context_switch_to加载第一个线程的时候使用。
```/*
 * void rt_hw_context_switch_to(rt_ubase_t to);
 * a0 --> to
 */
.globl rt_hw_context_switch_to
rt_hw_context_switch_to:
    LOAD sp, (a0)
    /* resw ra to mepc */
    LOAD tp,   0 * 4(sp) // 加载PC指针 到线程指针中 待用 
    LOAD x1,   1 * REGBYTES(sp) /* x1  - ra     - return address for jumps            */
    
    LOAD x5,   5 * REGBYTES(sp)
    LOAD x6,   6 * REGBYTES(sp)
    LOAD x7,   7 * REGBYTES(sp)
    LOAD x8,   8 * REGBYTES(sp)
    LOAD x9,   9 * REGBYTES(sp)
    LOAD x10, 10 * REGBYTES(sp)
    LOAD x11, 11 * REGBYTES(sp)
    LOAD x12, 12 * REGBYTES(sp)
    LOAD x13, 13 * REGBYTES(sp)
    LOAD x14, 14 * REGBYTES(sp)
    LOAD x15, 15 * REGBYTES(sp)
    LOAD x16, 16 * REGBYTES(sp)
    LOAD x17, 17 * REGBYTES(sp)
    LOAD x18, 18 * REGBYTES(sp)
    LOAD x19, 19 * REGBYTES(sp)
    LOAD x20, 20 * REGBYTES(sp)
    LOAD x21, 21 * REGBYTES(sp)
    LOAD x22, 22 * REGBYTES(sp)
    LOAD x23, 23 * REGBYTES(sp)
    LOAD x24, 24 * REGBYTES(sp)
    LOAD x25, 25 * REGBYTES(sp)
    LOAD x26, 26 * REGBYTES(sp)
    LOAD x27, 27 * REGBYTES(sp)
    LOAD x28, 28 * REGBYTES(sp)
    LOAD x29, 29 * REGBYTES(sp)
    LOAD x30, 30 * REGBYTES(sp)
    LOAD x31, 31 * REGBYTES(sp)

addi sp,  sp, 32 * REGBYTES
    jr tp // 跳转至线程指针```3、中断开关

```rt_base_t rt_hw_interrupt_disable(void)
{
    return riscv_maskirq(0xffffffff);
}
void rt_hw_interrupt_enable(rt_base_t level)
{
    riscv_maskirq(level);
    
    if(rt_hw_context_switch_flag)
    {
        rt_hw_context_switch_flag =0;
        if((level & 0x0002)==0)
        {
            /* 判断是否要触发系统中断*/
           if(rt_thread_switch_interrupt_flag)   
           {
                __asm("ecall");
           }
        }
    }
    return;
}
```

中断入口 实际进行线程切换的地方
```irq_entry:
        /* save registers */
    addi sp, sp, -32 * REGBYTES
    
        picorv32_setq_insn(q2, x1)
        
        picorv32_getq_insn(x1, q0)
        
        sw x1,   0*REGBYTES(sp)  // 保存 epc 指针
        
        picorv32_getq_insn(x1, q2)  // 保存 return address 
        sw x1,   1 * REGBYTES(sp)
        
        sw x5,   5 * REGBYTES(sp)
        sw x6,   6 * REGBYTES(sp)
        sw x7,   7 * REGBYTES(sp)
        sw x8,   8 * REGBYTES(sp)
        sw x9,   9 * REGBYTES(sp)
        sw x10, 10 * REGBYTES(sp)
        sw x11, 11 * REGBYTES(sp)
        sw x12, 12 * REGBYTES(sp)
        sw x13, 13 * REGBYTES(sp)
        sw x14, 14 * REGBYTES(sp)
        sw x15, 15 * REGBYTES(sp)
        sw x16, 16 * REGBYTES(sp)
        sw x17, 17 * REGBYTES(sp)
        sw x18, 18 * REGBYTES(sp)
        sw x19, 19 * REGBYTES(sp)
        sw x20, 20 * REGBYTES(sp)
        sw x21, 21 * REGBYTES(sp)
        sw x22, 22 * REGBYTES(sp)
        sw x23, 23 * REGBYTES(sp)
        sw x24, 24 * REGBYTES(sp)
        sw x25, 25 * REGBYTES(sp)
        sw x26, 26 * REGBYTES(sp)
        sw x27, 27 * REGBYTES(sp)
        sw x28, 28 * REGBYTES(sp)
        sw x29, 29 * REGBYTES(sp)
        sw x30, 30 * REGBYTES(sp)
        sw x31, 31 * REGBYTES(sp)
        
    picorv32_setq_insn(q3, x2) // 保存sp 至q3 寄存器

/* switch to interrupt stack */
    la sp , irq_stack // 加载 irq 堆栈

/* interrupt handle */
    call  rt_interrupt_enter
            /* call interrupt handler C function */
    picorv32_getq_insn(a1, q1)
        // call to C function
        jal ra, irq
    
    call  rt_interrupt_leave

/* switch to from thread stack */
    picorv32_getq_insn(sp, q3)
    /* need to switch new thread */
    la    s0, rt_thread_switch_interrupt_flag
    lw    s2, 0(s0)
    beqz  s2, rt_hw_context_switch_interrupt_exit
    /* clear switch interrupt flag */
    sw    zero, 0(s0)

la    s0, rt_interrupt_from_thread
    lw  s1, 0(s0)
    sw sp, 0(s1)

la    s0, rt_interrupt_to_thread
    lw  s1, 0(s0)
    lw  sp, 0(s1)

lw  a0,  0 * REGBYTES(sp)
    picorv32_setq_insn(q0, a0)

/* restore registers */
rt_hw_context_switch_interrupt_exit:

lw x1,   0 * REGBYTES(sp)
        picorv32_setq_insn(q0, x1)

lw x1,   1 * REGBYTES(sp)
        picorv32_setq_insn(q2, x1)

lw x5,   5 * REGBYTES(sp)
        lw x6,   6 * REGBYTES(sp)
        lw x7,   7 * REGBYTES(sp)
        lw x8,   8 * REGBYTES(sp)
        lw x9,   9 * REGBYTES(sp)
        lw x10, 10 * REGBYTES(sp)
        lw x11, 11 * REGBYTES(sp)
        lw x12, 12 * REGBYTES(sp)
        lw x13, 13 * REGBYTES(sp)
        lw x14, 14 * REGBYTES(sp)
        lw x15, 15 * REGBYTES(sp)
        lw x16, 16 * REGBYTES(sp)
        lw x17, 17 * REGBYTES(sp)
        lw x18, 18 * REGBYTES(sp)
        lw x19, 19 * REGBYTES(sp)
        lw x20, 20 * REGBYTES(sp)
        lw x21, 21 * REGBYTES(sp)
        lw x22, 22 * REGBYTES(sp)
        lw x23, 23 * REGBYTES(sp)
        lw x24, 24 * REGBYTES(sp)
        lw x25, 25 * REGBYTES(sp)
        lw x26, 26 * REGBYTES(sp)
        lw x27, 27 * REGBYTES(sp)
        lw x28, 28 * REGBYTES(sp)
        lw x29, 29 * REGBYTES(sp)
        lw x30, 30 * REGBYTES(sp)
        lw x31, 31 * REGBYTES(sp)
        
        picorv32_getq_insn(x1, q2)

addi  sp, sp, 32 * REGBYTES

picorv32_retirq_insn()

```运行效果 
安路FPGA上运行效果

![QQ截图20200701200411.png](https://oss-club.rt-thread.org/uploads/202007/01/200525eegk18boe87i1zbr.png)