// ==================================================================
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// Copyright (c) 2006-2011 by Lattice Semiconductor Corporation
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// FILE DETAILS
// Project : LatticeMico32
// File : lm32_dcache.v
// Title : Data cache
// Dependencies : lm32_include.v
// Version : 6.1.17
// : Initial Release
// Version : 7.0SP2, 3.0
// : No Change
// Version : 3.1
// : Support for user-selected resource usage when implementing
// : cache memory. Additional parameters must be defined when
// : invoking lm32_ram.v
// =============================================================================
`include "lm32_include.v"
`ifdef CFG_DCACHE_ENABLED
`define LM32_DC_ADDR_OFFSET_RNG addr_offset_msb:addr_offset_lsb
`define LM32_DC_ADDR_SET_RNG addr_set_msb:addr_set_lsb
`define LM32_DC_ADDR_TAG_RNG addr_tag_msb:addr_tag_lsb
`define LM32_DC_ADDR_IDX_RNG addr_set_msb:addr_offset_lsb
`define LM32_DC_TMEM_ADDR_WIDTH addr_set_width
`define LM32_DC_TMEM_ADDR_RNG (`LM32_DC_TMEM_ADDR_WIDTH-1):0
`define LM32_DC_DMEM_ADDR_WIDTH (addr_offset_width+addr_set_width)
`define LM32_DC_DMEM_ADDR_RNG (`LM32_DC_DMEM_ADDR_WIDTH-1):0
`define LM32_DC_TAGS_WIDTH (addr_tag_width+1)
`define LM32_DC_TAGS_RNG (`LM32_DC_TAGS_WIDTH-1):0
`define LM32_DC_TAGS_TAG_RNG (`LM32_DC_TAGS_WIDTH-1):1
`define LM32_DC_TAGS_VALID_RNG 0
`define LM32_DC_STATE_RNG 2:0
`define LM32_DC_STATE_FLUSH 3'b001
`define LM32_DC_STATE_CHECK 3'b010
`define LM32_DC_STATE_REFILL 3'b100
/////////////////////////////////////////////////////
// Module interface
/////////////////////////////////////////////////////
module lm32_dcache (
// ----- Inputs -----
clk_i,
rst_i,
stall_a,
stall_x,
stall_m,
address_x,
address_m,
load_q_m,
store_q_m,
store_data,
store_byte_select,
refill_ready,
refill_data,
dflush,
// ----- Outputs -----
stall_request,
restart_request,
refill_request,
refill_address,
refilling,
load_data
);
/////////////////////////////////////////////////////
// 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_DCACHE_LIMIT-`CFG_DCACHE_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 A stage
input stall_x; // Stall X stage
input stall_m; // Stall M stage
input [`LM32_WORD_RNG] address_x; // X stage load/store address
input [`LM32_WORD_RNG] address_m; // M stage load/store address
input load_q_m; // Load instruction in M stage
input store_q_m; // Store instruction in M stage
input [`LM32_WORD_RNG] store_data; // Data to store
input [`LM32_BYTE_SELECT_RNG] store_byte_select; // Which bytes in store data should be modified
input refill_ready; // Indicates next word of refill data is ready
input [`LM32_WORD_RNG] refill_data; // Refill data
input dflush; // Indicates cache should be flushed
/////////////////////////////////////////////////////
// Outputs
/////////////////////////////////////////////////////
output stall_request; // Request pipeline be stalled because cache is busy
wire stall_request;
output restart_request; // Request to restart instruction that caused the cache miss
reg restart_request;
output refill_request; // Request a refill
reg refill_request;
output [`LM32_WORD_RNG] refill_address; // Address to refill from
reg [`LM32_WORD_RNG] refill_address;
output refilling; // Indicates if the cache is currently refilling
reg refilling;
output [`LM32_WORD_RNG] load_data; // Data read from cache
wire [`LM32_WORD_RNG] load_data;
/////////////////////////////////////////////////////
// Internal nets and registers
/////////////////////////////////////////////////////
wire read_port_enable; // Cache memory read port clock enable
wire write_port_enable; // Cache memory write port clock enable
wire [0:associativity-1] way_tmem_we; // Tag memory write enable
wire [0:associativity-1] way_dmem_we; // Data memory write enable
wire [`LM32_WORD_RNG] way_data[0:associativity-1]; // Data read from data memory
wire [`LM32_DC_TAGS_TAG_RNG] way_tag[0:associativity-1];// Tag read from tag memory
wire [0:associativity-1] way_valid; // Indicates which ways are valid
wire [0:associativity-1] way_match; // Indicates which ways matched
wire miss; // Indicates no ways matched
wire [`LM32_DC_TMEM_ADDR_RNG] tmem_read_address; // Tag memory read address
wire [`LM32_DC_TMEM_ADDR_RNG] tmem_write_address; // Tag memory write address
wire [`LM32_DC_DMEM_ADDR_RNG] dmem_read_address; // Data memory read address
wire [`LM32_DC_DMEM_ADDR_RNG] dmem_write_address; // Data memory write address
wire [`LM32_DC_TAGS_RNG] tmem_write_data; // Tag memory write data
reg [`LM32_WORD_RNG] dmem_write_data; // Data memory write data
reg [`LM32_DC_STATE_RNG] state; // Current state of FSM
wire flushing; // Indicates if cache is currently flushing
wire check; // Indicates if cache is currently checking for hits/misses
wire refill; // Indicates if cache is currently refilling
wire valid_store; // Indicates if there is a valid store instruction
reg [associativity-1:0] refill_way_select; // Which way should be refilled
reg [`LM32_DC_ADDR_OFFSET_RNG] refill_offset; // Which word in cache line should be refilled
wire last_refill; // Indicates when on last cycle of cache refill
reg [`LM32_DC_TMEM_ADDR_RNG] flush_set; // Which set is currently being flushed
genvar i, j;
/////////////////////////////////////////////////////
// Functions
/////////////////////////////////////////////////////
`include "lm32_functions.v"
/////////////////////////////////////////////////////
// Instantiations
/////////////////////////////////////////////////////
generate
for (i = 0; i < associativity; i = i + 1)
begin : memories
// Way data
if (`LM32_DC_DMEM_ADDR_WIDTH < 11)
begin : data_memories
lm32_ram
#(
// ----- Parameters -------
.data_width (32),
.address_width (`LM32_DC_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 (read_port_enable),
.write_address (dmem_write_address),
.enable_write (write_port_enable),
.write_enable (way_dmem_we[i]),
.write_data (dmem_write_data),
// ----- Outputs -------
.read_data (way_data[i])
);
end
else
begin
for (j = 0; j < 4; j = j + 1)
begin : byte_memories
lm32_ram
#(
// ----- Parameters -------
.data_width (8),
.address_width (`LM32_DC_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 (read_port_enable),
.write_address (dmem_write_address),
.enable_write (write_port_enable),
.write_enable (way_dmem_we[i] & (store_byte_select[j] | refill)),
.write_data (dmem_write_data[(j+1)*8-1:j*8]),
// ----- Outputs -------
.read_data (way_data[i][(j+1)*8-1:j*8])
);
end
end
// Way tags
lm32_ram
#(
// ----- Parameters -------
.data_width (`LM32_DC_TAGS_WIDTH),
.address_width (`LM32_DC_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 (read_port_enable),
.write_address (tmem_write_address),
.enable_write (`TRUE),
.write_enable (way_tmem_we[i]),
.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 being read
generate
for (i = 0; i < associativity; i = i + 1)
begin : match
assign way_match[i] = ({way_tag[i], way_valid[i]} == {address_m[`LM32_DC_ADDR_TAG_RNG], `TRUE});
end
endgenerate
// Select data from way that matched the address being read
generate
if (associativity == 1)
begin : data_1
assign load_data = way_data[0];
end
else if (associativity == 2)
begin : data_2
assign load_data = way_match[0] ? way_data[0] : way_data[1];
end
endgenerate
generate
if (`LM32_DC_DMEM_ADDR_WIDTH < 11)
begin
// Select data to write to data memories
always @(*)
begin
if (refill == `TRUE)
dmem_write_data = refill_data;
else
begin
dmem_write_data[`LM32_BYTE_0_RNG] = store_byte_select[0] ? store_data[`LM32_BYTE_0_RNG] : load_data[`LM32_BYTE_0_RNG];
dmem_write_data[`LM32_BYTE_1_RNG] = store_byte_select[1] ? store_data[`LM32_BYTE_1_RNG] : load_data[`LM32_BYTE_1_RNG];
dmem_write_data[`LM32_BYTE_2_RNG] = store_byte_select[2] ? store_data[`LM32_BYTE_2_RNG] : load_data[`LM32_BYTE_2_RNG];
dmem_write_data[`LM32_BYTE_3_RNG] = store_byte_select[3] ? store_data[`LM32_BYTE_3_RNG] : load_data[`LM32_BYTE_3_RNG];
end
end
end
else
begin
// Select data to write to data memories - FIXME: Should use different write ports on dual port RAMs, but they don't work
always @(*)
begin
if (refill == `TRUE)
dmem_write_data = refill_data;
else
dmem_write_data = store_data;
end
end
endgenerate
// Compute address to use to index into the data memories
generate
if (bytes_per_line > 4)
assign dmem_write_address = (refill == `TRUE)
? {refill_address[`LM32_DC_ADDR_SET_RNG], refill_offset}
: address_m[`LM32_DC_ADDR_IDX_RNG];
else
assign dmem_write_address = (refill == `TRUE)
? refill_address[`LM32_DC_ADDR_SET_RNG]
: address_m[`LM32_DC_ADDR_IDX_RNG];
endgenerate
assign dmem_read_address = address_x[`LM32_DC_ADDR_IDX_RNG];
// Compute address to use to index into the tag memories
assign tmem_write_address = (flushing == `TRUE)
? flush_set
: refill_address[`LM32_DC_ADDR_SET_RNG];
assign tmem_read_address = address_x[`LM32_DC_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 read_port_enable = (stall_x == `FALSE);
assign write_port_enable = (refill_ready == `TRUE) || !stall_m;
// Determine when we have a valid store
assign valid_store = (store_q_m == `TRUE) && (check == `TRUE);
// Compute data and tag memory write enables
generate
if (associativity == 1)
begin : we_1
assign way_dmem_we[0] = (refill_ready == `TRUE) || ((valid_store == `TRUE) && (way_match[0] == `TRUE));
assign way_tmem_we[0] = (refill_ready == `TRUE) || (flushing == `TRUE);
end
else
begin : we_2
assign way_dmem_we[0] = ((refill_ready == `TRUE) && (refill_way_select[0] == `TRUE)) || ((valid_store == `TRUE) && (way_match[0] == `TRUE));
assign way_dmem_we[1] = ((refill_ready == `TRUE) && (refill_way_select[1] == `TRUE)) || ((valid_store == `TRUE) && (way_match[1] == `TRUE));
assign way_tmem_we[0] = ((refill_ready == `TRUE) && (refill_way_select[0] == `TRUE)) || (flushing == `TRUE);
assign way_tmem_we[1] = ((refill_ready == `TRUE) && (refill_way_select[1] == `TRUE)) || (flushing == `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_DC_TAGS_VALID_RNG] = ((last_refill == `TRUE) || (valid_store == `TRUE)) && (flushing == `FALSE);
assign tmem_write_data[`LM32_DC_TAGS_TAG_RNG] = refill_address[`LM32_DC_ADDR_TAG_RNG];
// Signals that indicate which state we are in
assign flushing = state[0];
assign check = state[1];
assign refill = state[2];
assign miss = (~(|way_match)) && (load_q_m == `TRUE) && (stall_m == `FALSE);
assign stall_request = (check == `FALSE);
/////////////////////////////////////////////////////
// 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 (refill_request == `TRUE)
refill_way_select <= {refill_way_select[0], refill_way_select[1]};
end
end
end
endgenerate
// Record whether we are currently 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_DC_STATE_FLUSH;
flush_set <= {`LM32_DC_TMEM_ADDR_WIDTH{1'b1}};
refill_request <= `FALSE;
refill_address <= {`LM32_WORD_WIDTH{1'bx}};
restart_request <= `FALSE;
end
else
begin
case (state)
// Flush the cache
`LM32_DC_STATE_FLUSH:
begin
if (flush_set == {`LM32_DC_TMEM_ADDR_WIDTH{1'b0}})
state <= `LM32_DC_STATE_CHECK;
flush_set <= flush_set - 1'b1;
end
// Check for cache misses
`LM32_DC_STATE_CHECK:
begin
if (stall_a == `FALSE)
restart_request <= `FALSE;
if (miss == `TRUE)
begin
refill_request <= `TRUE;
refill_address <= address_m;
state <= `LM32_DC_STATE_REFILL;
end
else if (dflush == `TRUE)
state <= `LM32_DC_STATE_FLUSH;
end
// Refill a cache line
`LM32_DC_STATE_REFILL:
begin
refill_request <= `FALSE;
if (refill_ready == `TRUE)
begin
if (last_refill == `TRUE)
begin
restart_request <= `TRUE;
state <= `LM32_DC_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_DC_STATE_CHECK:
begin
if (miss == `TRUE)
refill_offset <= {addr_offset_width{1'b0}};
end
// Refill a cache line
`LM32_DC_STATE_REFILL:
begin
if (refill_ready == `TRUE)
refill_offset <= refill_offset + 1'b1;
end
endcase
end
end
end
endgenerate
endmodule
`endif