【RISC-V设计-09】- RISC-V处理器设计K0A之CIC

【RISC-V设计-09】- RISC-V处理器设计K0A之CIC

1.简介

核内中断控制器（Core Interrupt Controller，简称CIC）是管理和仲裁中断的模块，能够根据预设的优先级规则，逐一上报中断请求的序号。本模块具有如下几点功能：

1. 根据全局中断使能，控制中断序号的上报；
2. 根据独立中断使能，控制对应的中断请求；
3. 记录中断状态，根据中断状态向指令译码单元发出中断请求；
4. 根据指令译码单元发出中断应答，清除中断请求；
5. 通过软件、硬件结合的方式，支持晚到中断、咬尾中断；

2.顶层设计

3.端口说明

4.代码设计

// -------------------------------------------------------------------------------------------------
// Copyright 2024 Kearn Chen, kearn.chen@aliyun.com
//
// 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
// 
//     http://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.
// -------------------------------------------------------------------------------------------------
// Description :
//             1. Core Interrupt Controller
// -------------------------------------------------------------------------------------------------

module k0a_core_cic (
    input  wire         core_clk        ,
    input  wire         core_rstn       ,

    input  wire [15:0]  irq_lines       ,

    input  wire         csr2cic_gie     ,
    input  wire [15:0]  csr2cic_mie     ,
    input  wire [15:0]  csr2cic_mip     ,
    output wire [15:0]  cic2csr_irq     ,
    output reg  [4:0]   cic2csr_mcause  ,

    output reg          cic2idu_int_req ,
    input  wire         idu2cic_int_ack ,
    input  wire         idu2cic_int_mret
);

reg     status_irq;

wire cic_int_hit = cic2idu_int_req & idu2cic_int_ack;

wire [15:0] irq_src = csr2cic_mip & csr2cic_mie;

assign cic2csr_irq = irq_lines;

always @(posedge core_clk or negedge core_rstn)
begin
    if(!core_rstn)
        status_irq <= 1'b0;
    else if(cic_int_hit)
        status_irq <= 1'b1;
    else if(idu2cic_int_mret)
        status_irq <= 1'b0;
end

always @(posedge core_clk)
begin
    if(csr2cic_gie) begin
        case(1'b1)
            irq_src[ 0] : cic2csr_mcause <= {1'b1, 4'h0};
            irq_src[ 1] : cic2csr_mcause <= {1'b1, 4'h1};
            irq_src[ 2] : cic2csr_mcause <= {1'b1, 4'h2};
            irq_src[ 3] : cic2csr_mcause <= {1'b1, 4'h3};
            irq_src[ 4] : cic2csr_mcause <= {1'b1, 4'h4};
            irq_src[ 5] : cic2csr_mcause <= {1'b1, 4'h5};
            irq_src[ 6] : cic2csr_mcause <= {1'b1, 4'h6};
            irq_src[ 7] : cic2csr_mcause <= {1'b1, 4'h7};
            irq_src[ 8] : cic2csr_mcause <= {1'b1, 4'h8};
            irq_src[ 9] : cic2csr_mcause <= {1'b1, 4'h9};
            irq_src[10] : cic2csr_mcause <= {1'b1, 4'ha};
            irq_src[11] : cic2csr_mcause <= {1'b1, 4'hb};
            irq_src[12] : cic2csr_mcause <= {1'b1, 4'hc};
            irq_src[13] : cic2csr_mcause <= {1'b1, 4'hd};
            irq_src[14] : cic2csr_mcause <= {1'b1, 4'he};
            irq_src[15] : cic2csr_mcause <= {1'b1, 4'hf};
            default     : cic2csr_mcause <= 5'd0;
        endcase
    end
end

always @(posedge core_clk or negedge core_rstn)
begin
    if(!core_rstn)
        cic2idu_int_req <= 1'b0;
    else if(cic_int_hit)
        cic2idu_int_req <= 1'b0;
    else if(~status_irq & (|irq_src))
        cic2idu_int_req <= 1'b1;
end

endmodule

5.仲裁代码

# -------------------------------------------------------------------------------------------------
# Copyright 2024 Kearn Chen, kearn.chen@aliyun.com
#
# 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
# 
#     http://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.
# -------------------------------------------------------------------------------------------------

	.section .init, "ax", @progbits
	.globl  _start
	.align  2
_start:
	.option norvc;
    j       handler_reset
    .word   handler_irq0
    .word   handler_irq1
    .word   handler_irq2
    .word   handler_irq3
    .word   handler_irq4
    .word   handler_irq5
    .word   handler_irq6
    .word   handler_irq7
    .word   handler_irq8
    .word   handler_irq9
    .word   handler_irq10
    .word   handler_irq11
    .word   handler_irq12
    .word   handler_irq13
    .word   handler_irq14
    .word   handler_irq15

	.section .text.handler_isr, "ax", @progbits
	.align    2
handler_isr:
    addi sp, sp, -56
    sw x1 , 0(sp)
    sw x4 , 4(sp)
    sw x5 , 8(sp)
    sw x6 , 12(sp)
    sw x7 , 16(sp)
    sw x8 , 20(sp)
    sw x9 , 24(sp)
    sw x10, 28(sp)
    sw x11, 32(sp)
    sw x12, 36(sp)
    sw x13, 40(sp)
    sw x14, 44(sp)
    sw x15, 48(sp)
1:
    csrr a0, mcause
    beq x0, a0, 2f
    andi a0, a0, 15
    addi a1, x0, 1
    sll a2, a1, a0
    csrrc a2, mip, a2
    slli a0, a0, 2
    lw a1, 4(a0)
    jalr ra, a1, 0
    jal x0, 1b
2:
    lw x15, 48(sp)
    lw x14, 44(sp)
    lw x13, 40(sp)
    lw x12, 36(sp)
    lw x11, 32(sp)
    lw x10, 28(sp)
    lw x9 , 24(sp)
    lw x8 , 20(sp)
    lw x7 , 16(sp)
    lw x6 , 12(sp)
    lw x5 , 8(sp)
    lw x4 , 4(sp)
    lw x1 , 0(sp)
    addi sp, sp, 56
    mret

	.section .text.handler_default, "ax", @progbits
	.align    2
	.weak   handler_irq0
	.weak   handler_irq1
	.weak   handler_irq2
	.weak   handler_irq3
	.weak   handler_irq4
	.weak   handler_irq5
	.weak   handler_irq6
	.weak   handler_irq7
	.weak   handler_irq8
	.weak   handler_irq9
	.weak   handler_irq10
	.weak   handler_irq11
	.weak   handler_irq12
	.weak   handler_irq13
	.weak   handler_irq14
	.weak   handler_irq15
handler_irq0:
handler_irq1:
handler_irq2:
handler_irq3:
handler_irq4:
handler_irq5:
handler_irq6:
handler_irq7:
handler_irq8:
handler_irq9:
handler_irq10:
handler_irq11:
handler_irq12:
handler_irq13:
handler_irq14:
handler_irq15:
loop_isr:
	j loop_isr

	.section  .text.handler_reset, "ax", @progbits
	.align    2
handler_reset:
.option push
.option norelax
	la gp, __global_pointer$
.option pop
1:
	la sp, _eusrstack
2:
	la a0, _data_lma
	la a1, _data_vma
	la a2, _edata
	bgeu a1, a2, 2f
1:
	lw a3, 0(a0)
	sw a3, 0(a1)
	addi a0, a0, 4
	addi a1, a1, 4
	bgeu a1, a2, 2f
	lw a3, 0(a0)
	sw a3, 0(a1)
	addi a0, a0, 4
	addi a1, a1, 4
	bltu a1, a2, 1b
2:
    la a0, _sbss
    la a1, _ebss
    bgeu a0, a1, 2f
1:
    sw x0, 0(a0)
    addi a0, a0, 4
    bgeu a0, a1, 2f
    sw x0, 0(a0)
    addi a0, a0, 4
    bgeu a0, a1, 2f
    sw x0, 0(a0)
    addi a0, a0, 4
    bltu a0, a1, 1b
2:
    la a3, handler_isr
    csrw mtvec, a3

    j main

这段代码是开始运行时初始化的代码，同时还存在中断处理相关的操作，通过读取中断原因、进行一些位操作确定中断序号。如果中断原因不为 0，根据中断序号查找到中断向量表，跳转到特定的地址执行相应的中断处理程序。

6.总结

本文阐述了一种极为简洁的中断控制模块。该模块采用软件与硬件相结合的方式，来达成中断的处理。并且，它还能够支持晚到中断和咬尾中断，一次进出栈就能够处置多个现存的中断。如此一来，节省了中断处理的时间，提高了中断处理的效率。