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litex/verilog/lm32/lm32_icache.v

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// ==================================================================
// >>>>>>>>>>>>>>>>>>>>>>> COPYRIGHT NOTICE <<<<<<<<<<<<<<<<<<<<<<<<<
// ------------------------------------------------------------------
// Copyright (c) 2006-2011 by Lattice Semiconductor Corporation
// ALL RIGHTS RESERVED
// ------------------------------------------------------------------
//
// IMPORTANT: THIS FILE IS AUTO-GENERATED BY THE LATTICEMICO SYSTEM.
//
// Permission:
//
// Lattice Semiconductor grants permission to use this code
// pursuant to the terms of the Lattice Semiconductor Corporation
// Open Source License Agreement.
//
// Disclaimer:
//
// Lattice Semiconductor provides no warranty regarding the use or
// functionality of this code. It is the user's responsibility to
// verify the user's design for consistency and functionality through
// the use of formal verification methods.
//
// --------------------------------------------------------------------
//
// Lattice Semiconductor Corporation
// 5555 NE Moore Court
// Hillsboro, OR 97214
// U.S.A
//
// TEL: 1-800-Lattice (USA and Canada)
// 503-286-8001 (other locations)
//
// web: http://www.latticesemi.com/
// email: techsupport@latticesemi.com
//
// --------------------------------------------------------------------
// FILE DETAILS
// Project : LatticeMico32
// File : lm32_icache.v
// Title : Instruction cache
// Dependencies : lm32_include.v
//
// Version 3.5
// 1. Bug Fix: Instruction cache flushes issued from Instruction Inline Memory
// cause segmentation fault due to incorrect fetches.
//
// Version 3.1
// 1. Feature: Support for user-selected resource usage when implementing
// cache memory. Additional parameters must be defined when invoking module
// lm32_ram. Instruction cache miss mechanism is dependent on branch
// prediction being performed in D stage of pipeline.
//
// Version 7.0SP2, 3.0
// No change
// =============================================================================
`include "lm32_include.v"
`ifdef CFG_ICACHE_ENABLED
`define LM32_IC_ADDR_OFFSET_RNG addr_offset_msb:addr_offset_lsb
`define LM32_IC_ADDR_SET_RNG addr_set_msb:addr_set_lsb
`define LM32_IC_ADDR_TAG_RNG addr_tag_msb:addr_tag_lsb
`define LM32_IC_ADDR_IDX_RNG addr_set_msb:addr_offset_lsb
`define LM32_IC_TMEM_ADDR_WIDTH addr_set_width
`define LM32_IC_TMEM_ADDR_RNG (`LM32_IC_TMEM_ADDR_WIDTH-1):0
`define LM32_IC_DMEM_ADDR_WIDTH (addr_offset_width+addr_set_width)
`define LM32_IC_DMEM_ADDR_RNG (`LM32_IC_DMEM_ADDR_WIDTH-1):0
`define LM32_IC_TAGS_WIDTH (addr_tag_width+1)
`define LM32_IC_TAGS_RNG (`LM32_IC_TAGS_WIDTH-1):0
`define LM32_IC_TAGS_TAG_RNG (`LM32_IC_TAGS_WIDTH-1):1
`define LM32_IC_TAGS_VALID_RNG 0
`define LM32_IC_STATE_RNG 3:0
`define LM32_IC_STATE_FLUSH_INIT 4'b0001
`define LM32_IC_STATE_FLUSH 4'b0010
`define LM32_IC_STATE_CHECK 4'b0100
`define LM32_IC_STATE_REFILL 4'b1000
/////////////////////////////////////////////////////
// Module interface
/////////////////////////////////////////////////////
module lm32_icache (
// ----- Inputs -----
clk_i,
rst_i,
stall_a,
stall_f,
address_a,
address_f,
read_enable_f,
refill_ready,
refill_data,
iflush,
`ifdef CFG_IROM_ENABLED
select_f,
`endif
valid_d,
branch_predict_taken_d,
// ----- Outputs -----
stall_request,
restart_request,
refill_request,
refill_address,
refilling,
inst
);
/////////////////////////////////////////////////////
// Parameters
/////////////////////////////////////////////////////
parameter associativity = 1; // Associativity of the cache (Number of ways)
parameter sets = 512; // Number of sets
parameter bytes_per_line = 16; // Number of bytes per cache line
parameter base_address = 0; // Base address of cachable memory
parameter limit = 0; // Limit (highest address) of cachable memory
localparam addr_offset_width = clogb2(bytes_per_line)-1-2;
localparam addr_set_width = clogb2(sets)-1;
localparam addr_offset_lsb = 2;
localparam addr_offset_msb = (addr_offset_lsb+addr_offset_width-1);
localparam addr_set_lsb = (addr_offset_msb+1);
localparam addr_set_msb = (addr_set_lsb+addr_set_width-1);
localparam addr_tag_lsb = (addr_set_msb+1);
localparam addr_tag_msb = clogb2(`CFG_ICACHE_LIMIT-`CFG_ICACHE_BASE_ADDRESS)-1;
localparam addr_tag_width = (addr_tag_msb-addr_tag_lsb+1);
/////////////////////////////////////////////////////
// Inputs
/////////////////////////////////////////////////////
input clk_i; // Clock
input rst_i; // Reset
input stall_a; // Stall instruction in A stage
input stall_f; // Stall instruction in F stage
input valid_d; // Valid instruction in D stage
input branch_predict_taken_d; // Instruction in D stage is a branch and is predicted taken
input [`LM32_PC_RNG] address_a; // Address of instruction in A stage
input [`LM32_PC_RNG] address_f; // Address of instruction in F stage
input read_enable_f; // Indicates if cache access is valid
input refill_ready; // Next word of refill data is ready
input [`LM32_INSTRUCTION_RNG] refill_data; // Data to refill the cache with
input iflush; // Flush the cache
`ifdef CFG_IROM_ENABLED
input select_f; // Instruction in F stage is mapped through instruction cache
`endif
/////////////////////////////////////////////////////
// Outputs
/////////////////////////////////////////////////////
output stall_request; // Request to stall the pipeline
wire stall_request;
output restart_request; // Request to restart instruction that caused the cache miss
reg restart_request;
output refill_request; // Request to refill a cache line
wire refill_request;
output [`LM32_PC_RNG] refill_address; // Base address of cache refill
reg [`LM32_PC_RNG] refill_address;
output refilling; // Indicates the instruction cache is currently refilling
reg refilling;
output [`LM32_INSTRUCTION_RNG] inst; // Instruction read from cache
wire [`LM32_INSTRUCTION_RNG] inst;
/////////////////////////////////////////////////////
// Internal nets and registers
/////////////////////////////////////////////////////
wire enable;
wire [0:associativity-1] way_mem_we;
wire [`LM32_INSTRUCTION_RNG] way_data[0:associativity-1];
wire [`LM32_IC_TAGS_TAG_RNG] way_tag[0:associativity-1];
wire [0:associativity-1] way_valid;
wire [0:associativity-1] way_match;
wire miss;
wire [`LM32_IC_TMEM_ADDR_RNG] tmem_read_address;
wire [`LM32_IC_TMEM_ADDR_RNG] tmem_write_address;
wire [`LM32_IC_DMEM_ADDR_RNG] dmem_read_address;
wire [`LM32_IC_DMEM_ADDR_RNG] dmem_write_address;
wire [`LM32_IC_TAGS_RNG] tmem_write_data;
reg [`LM32_IC_STATE_RNG] state;
wire flushing;
wire check;
wire refill;
reg [associativity-1:0] refill_way_select;
reg [`LM32_IC_ADDR_OFFSET_RNG] refill_offset;
wire last_refill;
reg [`LM32_IC_TMEM_ADDR_RNG] flush_set;
genvar i;
/////////////////////////////////////////////////////
// Functions
/////////////////////////////////////////////////////
`include "lm32_functions.v"
/////////////////////////////////////////////////////
// Instantiations
/////////////////////////////////////////////////////
generate
for (i = 0; i < associativity; i = i + 1)
begin : memories
lm32_ram
#(
// ----- Parameters -------
.data_width (32),
.address_width (`LM32_IC_DMEM_ADDR_WIDTH)
// Modified for Milkymist: removed non-portable RAM parameters
)
way_0_data_ram
(
// ----- Inputs -------
.read_clk (clk_i),
.write_clk (clk_i),
.reset (rst_i),
.read_address (dmem_read_address),
.enable_read (enable),
.write_address (dmem_write_address),
.enable_write (`TRUE),
.write_enable (way_mem_we[i]),
.write_data (refill_data),
// ----- Outputs -------
.read_data (way_data[i])
);
lm32_ram
#(
// ----- Parameters -------
.data_width (`LM32_IC_TAGS_WIDTH),
.address_width (`LM32_IC_TMEM_ADDR_WIDTH)
// Modified for Milkymist: removed non-portable RAM parameters
)
way_0_tag_ram
(
// ----- Inputs -------
.read_clk (clk_i),
.write_clk (clk_i),
.reset (rst_i),
.read_address (tmem_read_address),
.enable_read (enable),
.write_address (tmem_write_address),
.enable_write (`TRUE),
.write_enable (way_mem_we[i] | flushing),
.write_data (tmem_write_data),
// ----- Outputs -------
.read_data ({way_tag[i], way_valid[i]})
);
end
endgenerate
/////////////////////////////////////////////////////
// Combinational logic
/////////////////////////////////////////////////////
// Compute which ways in the cache match the address address being read
generate
for (i = 0; i < associativity; i = i + 1)
begin : match
assign way_match[i] = ({way_tag[i], way_valid[i]} == {address_f[`LM32_IC_ADDR_TAG_RNG], `TRUE});
end
endgenerate
// Select data from way that matched the address being read
generate
if (associativity == 1)
begin : inst_1
assign inst = way_match[0] ? way_data[0] : 32'b0;
end
else if (associativity == 2)
begin : inst_2
assign inst = way_match[0] ? way_data[0] : (way_match[1] ? way_data[1] : 32'b0);
end
endgenerate
// Compute address to use to index into the data memories
generate
if (bytes_per_line > 4)
assign dmem_write_address = {refill_address[`LM32_IC_ADDR_SET_RNG], refill_offset};
else
assign dmem_write_address = refill_address[`LM32_IC_ADDR_SET_RNG];
endgenerate
assign dmem_read_address = address_a[`LM32_IC_ADDR_IDX_RNG];
// Compute address to use to index into the tag memories
assign tmem_read_address = address_a[`LM32_IC_ADDR_SET_RNG];
assign tmem_write_address = flushing
? flush_set
: refill_address[`LM32_IC_ADDR_SET_RNG];
// Compute signal to indicate when we are on the last refill accesses
generate
if (bytes_per_line > 4)
assign last_refill = refill_offset == {addr_offset_width{1'b1}};
else
assign last_refill = `TRUE;
endgenerate
// Compute data and tag memory access enable
assign enable = (stall_a == `FALSE);
// Compute data and tag memory write enables
generate
if (associativity == 1)
begin : we_1
assign way_mem_we[0] = (refill_ready == `TRUE);
end
else
begin : we_2
assign way_mem_we[0] = (refill_ready == `TRUE) && (refill_way_select[0] == `TRUE);
assign way_mem_we[1] = (refill_ready == `TRUE) && (refill_way_select[1] == `TRUE);
end
endgenerate
// On the last refill cycle set the valid bit, for all other writes it should be cleared
assign tmem_write_data[`LM32_IC_TAGS_VALID_RNG] = last_refill & !flushing;
assign tmem_write_data[`LM32_IC_TAGS_TAG_RNG] = refill_address[`LM32_IC_ADDR_TAG_RNG];
// Signals that indicate which state we are in
assign flushing = |state[1:0];
assign check = state[2];
assign refill = state[3];
assign miss = (~(|way_match)) && (read_enable_f == `TRUE) && (stall_f == `FALSE) && !(valid_d && branch_predict_taken_d);
assign stall_request = (check == `FALSE);
assign refill_request = (refill == `TRUE);
/////////////////////////////////////////////////////
// Sequential logic
/////////////////////////////////////////////////////
// Record way selected for replacement on a cache miss
generate
if (associativity >= 2)
begin : way_select
always @(posedge clk_i `CFG_RESET_SENSITIVITY)
begin
if (rst_i == `TRUE)
refill_way_select <= {{associativity-1{1'b0}}, 1'b1};
else
begin
if (miss == `TRUE)
refill_way_select <= {refill_way_select[0], refill_way_select[1]};
end
end
end
endgenerate
// Record whether we are refilling
always @(posedge clk_i `CFG_RESET_SENSITIVITY)
begin
if (rst_i == `TRUE)
refilling <= `FALSE;
else
refilling <= refill;
end
// Instruction cache control FSM
always @(posedge clk_i `CFG_RESET_SENSITIVITY)
begin
if (rst_i == `TRUE)
begin
state <= `LM32_IC_STATE_FLUSH_INIT;
flush_set <= {`LM32_IC_TMEM_ADDR_WIDTH{1'b1}};
refill_address <= {`LM32_PC_WIDTH{1'bx}};
restart_request <= `FALSE;
end
else
begin
case (state)
// Flush the cache for the first time after reset
`LM32_IC_STATE_FLUSH_INIT:
begin
if (flush_set == {`LM32_IC_TMEM_ADDR_WIDTH{1'b0}})
state <= `LM32_IC_STATE_CHECK;
flush_set <= flush_set - 1'b1;
end
// Flush the cache in response to an write to the ICC CSR
`LM32_IC_STATE_FLUSH:
begin
if (flush_set == {`LM32_IC_TMEM_ADDR_WIDTH{1'b0}})
`ifdef CFG_IROM_ENABLED
if (select_f)
state <= `LM32_IC_STATE_REFILL;
else
`endif
state <= `LM32_IC_STATE_CHECK;
flush_set <= flush_set - 1'b1;
end
// Check for cache misses
`LM32_IC_STATE_CHECK:
begin
if (stall_a == `FALSE)
restart_request <= `FALSE;
if (iflush == `TRUE)
begin
refill_address <= address_f;
state <= `LM32_IC_STATE_FLUSH;
end
else if (miss == `TRUE)
begin
refill_address <= address_f;
state <= `LM32_IC_STATE_REFILL;
end
end
// Refill a cache line
`LM32_IC_STATE_REFILL:
begin
if (refill_ready == `TRUE)
begin
if (last_refill == `TRUE)
begin
restart_request <= `TRUE;
state <= `LM32_IC_STATE_CHECK;
end
end
end
endcase
end
end
generate
if (bytes_per_line > 4)
begin
// Refill offset
always @(posedge clk_i `CFG_RESET_SENSITIVITY)
begin
if (rst_i == `TRUE)
refill_offset <= {addr_offset_width{1'b0}};
else
begin
case (state)
// Check for cache misses
`LM32_IC_STATE_CHECK:
begin
if (iflush == `TRUE)
refill_offset <= {addr_offset_width{1'b0}};
else if (miss == `TRUE)
refill_offset <= {addr_offset_width{1'b0}};
end
// Refill a cache line
`LM32_IC_STATE_REFILL:
begin
if (refill_ready == `TRUE)
refill_offset <= refill_offset + 1'b1;
end
endcase
end
end
end
endgenerate
endmodule
`endif
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