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FPGA-Neural/rtl/neuron_memory.v
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micheleandClaude Sonnet 5 7e2711fa27 feat: widen ADDR_WIDTH to 23 bits for full 8MB PSRAM addressing 
Bumps ADDR_WIDTH's default from 22 to 23 bits across every RTL
module (neuron_memory, layer_sequencer, spi_engine, spi_neuron_top,
mem_arbiter, int8_memory_access, memory_interface, psram_controller,
memory_model) and every testbench that mirrors it, so the system's
byte-address space reaches the full 8 MiB the recommended PSRAM part
(ISSI IS66WVE4M16EBLL-70BLI, docs/FPGA-Neural-Hardware-Design.md §3)
actually provides -- previously only 4 MiB (half the chip) was
reachable, since int8_memory_access.v's byte->word address shift
(addr >> 1) turned the old 22-bit byte address into only 21 real word
bits, one short of the chip's real 22-bit word address (A0-A21). At
23 bits, that same shift lands exactly on all 22 chip address lines,
so the whole part is usable now instead of deferred to a future
widening.

Also fixes a stray 22'd11-sized literal in layer_sequencer.v's
descriptor-table address increment (numerically already safe via
Verilog's zero-extension, but now correctly unsized so it always
matches ADDR_WIDTH instead of silently assuming 22).

Updated docs/FPGA-NeuralNetwork-Engine.md's SPI protocol address-field
note (23 bits, top 1 reserved bit instead of 2) and
docs/FPGA-Neural-Hardware-Design.md's PSRAM section (the "chip has
one spare address line" framing is gone now that all 22 are wired
and used).

Full regression (all 11 ADDR_WIDTH-touching testbenches, plus a
Yosys elaboration check of spi_neuron_top with the new default and
no override) passes clean.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WQV3vS9TXaGDJ5cRfnfidt
2026-09-02 21:00:46 +02:00

499 lines
15 KiB
Verilog
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`timescale 1ns/1ps
module neuron_memory #(
parameter ADDR_WIDTH = 23,
parameter DATA_WIDTH = 8,
parameter N_INPUTS = 32,
parameter N_NEURONS = 1,
parameter PARALLEL = 8,
parameter ACC_WIDTH = 32
)(
input wire clk,
input wire rst,
input wire start,
// ------------------------------------------------------------
// Memory interface
//
// BYTE-ADDRESS / INT8 interface
// ------------------------------------------------------------
output wire mem_req,
output wire mem_wr,
output wire [ADDR_WIDTH-1:0] mem_addr,
output wire signed [7:0] mem_wdata,
input wire signed [7:0] mem_rdata,
input wire mem_ready,
// ------------------------------------------------------------
// Network memory layout
// ------------------------------------------------------------
input wire [ADDR_WIDTH-1:0] x_base,
input wire [ADDR_WIDTH-1:0] w_base,
input wire [ADDR_WIDTH-1:0] bias_addr,
// Activation function for this run, forwarded to neuron_parallel
// (see rtl/neuron_parallel.v's ACT_* localparams). Defaults to
// ACT_RELU (2'd1), neuron_parallel's own default, so any caller
// that leaves this unconnected is unaffected.
input wire [1:0] activation = 2'd1,
// Real (runtime) width for THIS run: how many of the N_INPUTS/
// N_NEURONS this instance was BUILT for are actually real for
// the network currently loaded. Lets one synthesized bitstream
// serve any network topology up to its build-time max width --
// X/W are read from RAM for n_inputs_real elements per neuron
// (not N_INPUTS), and only n_neurons_real neurons are computed
// (not N_NEURONS); n_inputs_real must be a multiple of PARALLEL
// (the caller's responsibility -- same constraint N_INPUTS
// itself is held to at elaboration time, see
// rtl/neuron_parallel.v's PARAMETER GUARD). Defaults to the
// full build-time width, so any caller that leaves these
// unconnected is completely unaffected.
input wire [15:0] n_inputs_real = N_INPUTS[15:0],
input wire [15:0] n_neurons_real = N_NEURONS[15:0],
// ------------------------------------------------------------
// Result
//
// One INT8 output per neuron, packed neuron-major (same
// convention as layer.v's y_bus): neuron n occupies
// y_bus[n*DATA_WIDTH +: DATA_WIDTH].
// ------------------------------------------------------------
output wire signed [DATA_WIDTH*N_NEURONS-1:0] y_bus,
output reg busy,
output reg done
);
// ============================================================
// STATES
// ============================================================
localparam STATE_IDLE = 4'd0;
localparam STATE_READ_X = 4'd1;
localparam STATE_READ_W = 4'd2;
localparam STATE_READ_BIAS = 4'd3;
localparam STATE_START_N = 4'd4;
localparam STATE_WAIT_N = 4'd5;
reg [3:0] state;
reg [$clog2(N_INPUTS+1)-1:0] index;
// ============================================================
// NEURON LOOP (Phase 3: multi-neuron memory integration)
//
// X is shared and read once per layer invocation. W and bias
// are re-read from memory for each neuron in turn and fed to a
// single, reused neuron_parallel instance (memory-bound design:
// one neuron computed at a time). w_group_base/bias_group_addr
// track the current neuron's base address and are advanced by
// N_INPUTS / 1 byte respectively between neurons, following the
// same neuron-major layout as layer.v's weights_bus/bias_bus.
// ============================================================
localparam NEURON_INDEX_WIDTH =
(N_NEURONS <= 1) ? 1 : $clog2(N_NEURONS);
reg [NEURON_INDEX_WIDTH-1:0] neuron_index;
reg [ADDR_WIDTH-1:0] w_group_base;
reg [ADDR_WIDTH-1:0] bias_group_addr;
reg signed [7:0] y_reg [0:N_NEURONS-1];
// ============================================================
// LOCAL MEMORY ARRAYS
// ============================================================
reg signed [7:0] x_mem [0:N_INPUTS-1];
reg signed [7:0] w_mem [0:N_INPUTS-1];
reg signed [7:0] bias_reg;
// ============================================================
// NEURON BUS
// ============================================================
wire signed [DATA_WIDTH*N_INPUTS-1:0] x_bus;
wire signed [DATA_WIDTH*N_INPUTS-1:0] w_bus;
genvar i;
generate
for (i = 0; i < N_INPUTS; i = i + 1) begin : GEN_BUS
assign x_bus[i*DATA_WIDTH +: DATA_WIDTH] = x_mem[i];
assign w_bus[i*DATA_WIDTH +: DATA_WIDTH] = w_mem[i];
end
endgenerate
genvar j;
generate
for (j = 0; j < N_NEURONS; j = j + 1) begin : GEN_Y_BUS
assign y_bus[j*DATA_WIDTH +: DATA_WIDTH] = y_reg[j];
end
endgenerate
// ============================================================
// INT8 MEMORY ACCESS
//
// This converts BYTE addresses into 16-bit word accesses.
//
// IMPORTANT:
// The memory side of this block is connected to the EXTERNAL
// memory_interface through the neuron_memory ports.
//
// It must NOT be connected directly to the PSRAM controller.
// ============================================================
reg access_req;
reg access_wr;
reg [ADDR_WIDTH-1:0] access_addr;
reg signed [7:0] access_wdata;
wire signed [7:0] access_rdata;
wire access_ready;
wire access_mem_req;
wire access_mem_wr;
wire [ADDR_WIDTH-1:0] access_mem_addr;
wire [15:0] access_mem_wdata;
wire access_mem_lb_n;
wire access_mem_ub_n;
// ------------------------------------------------------------
// Return data from the external memory interface.
//
// memory_interface returns a 16-bit word, while neuron_memory
// exposes only the requested INT8 byte.
//
// int8_memory_access expects the complete 16-bit word.
// ------------------------------------------------------------
wire [15:0] access_mem_rdata;
assign access_mem_rdata =
access_addr[0]
? {mem_rdata, 8'h00}
: {8'h00, mem_rdata};
// ------------------------------------------------------------
// IMPORTANT:
//
// mem_ready comes from the EXTERNAL memory_interface.
// mem_rdata comes from the EXTERNAL memory_interface.
//
// This fixes the previous deadlock where int8_memory_access
// was waiting for the PSRAM controller's mem_ready directly.
// ------------------------------------------------------------
int8_memory_access #(
.ADDR_WIDTH(ADDR_WIDTH)
) u_mem (
.clk (clk),
.rst (rst),
.req (access_req),
.wr (access_wr),
.addr (access_addr),
.wdata (access_wdata),
.rdata (access_rdata),
.ready (access_ready),
.mem_req (access_mem_req),
.mem_wr (access_mem_wr),
.mem_addr (access_mem_addr),
.mem_wdata (access_mem_wdata),
.mem_lb_n (access_mem_lb_n),
.mem_ub_n (access_mem_ub_n),
.mem_rdata (access_mem_rdata),
.mem_ready (mem_ready)
);
// ============================================================
// EXTERNAL MEMORY INTERFACE
//
// The external interface expects the INT8-level signals.
// The testbench converts these into its 16-bit bus.
//
// IMPORTANT:
// access_mem_addr is already a WORD address.
// However, the external neuron_memory interface is defined
// as a BYTE address.
//
// Therefore expose the original byte address here.
// ============================================================
assign mem_req = access_mem_req;
assign mem_wr = access_mem_wr;
assign mem_addr =
access_addr;
assign mem_wdata =
access_wdata;
// ============================================================
// NEURON
// ============================================================
reg neuron_start;
integer rst_i;
wire signed [7:0] neuron_y;
wire neuron_busy;
wire neuron_done;
neuron_parallel #(
.DATA_WIDTH(DATA_WIDTH),
.N_INPUTS(N_INPUTS),
.PARALLEL(PARALLEL),
.ACC_WIDTH(ACC_WIDTH)
) u_neuron (
.clk(clk),
.rst(rst),
.start(neuron_start),
.x_bus(x_bus),
.w_bus(w_bus),
.bias(bias_reg),
.activation(activation),
.n_inputs_real(n_inputs_real),
.y(neuron_y),
.busy(neuron_busy),
.done(neuron_done)
);
// ============================================================
// CONTROLLER
// ============================================================
always @(posedge clk) begin
if (rst) begin
state <= STATE_IDLE;
index <= 0;
neuron_index <= 0;
w_group_base <= 0;
bias_group_addr <= 0;
bias_reg <= 0;
access_req <= 1'b0;
access_wr <= 1'b0;
access_addr <= 0;
access_wdata <= 0;
neuron_start <= 1'b0;
for (rst_i = 0; rst_i < N_NEURONS; rst_i = rst_i + 1)
y_reg[rst_i] <= 0;
busy <= 1'b0;
done <= 1'b0;
end else begin
// ----------------------------------------------------
// Default pulse signals
// ----------------------------------------------------
access_req <= 1'b0;
neuron_start <= 1'b0;
done <= 1'b0;
case (state)
// =================================================
// IDLE
// =================================================
STATE_IDLE: begin
busy <= 1'b0;
if (start) begin
busy <= 1'b1;
index <= 0;
neuron_index <= 0;
w_group_base <= w_base;
bias_group_addr <= bias_addr;
// First X byte
access_addr <= x_base;
access_wr <= 1'b0;
access_req <= 1'b1;
state <= STATE_READ_X;
end
end
// =================================================
// READ X
// =================================================
STATE_READ_X: begin
if (access_ready) begin
x_mem[index] <= access_rdata;
if (index == n_inputs_real[$clog2(N_INPUTS+1)-1:0]-1'b1) begin
index <= 0;
access_addr <= w_group_base;
access_wr <= 1'b0;
access_req <= 1'b1;
state <= STATE_READ_W;
end else begin
index <= index + 1'b1;
access_addr <= x_base + index + 1'b1;
access_req <= 1'b1;
end
end
end
// =================================================
// READ W
// =================================================
STATE_READ_W: begin
if (access_ready) begin
w_mem[index] <= access_rdata;
if (index == n_inputs_real[$clog2(N_INPUTS+1)-1:0]-1'b1) begin
access_addr <= bias_group_addr;
access_wr <= 1'b0;
access_req <= 1'b1;
state <= STATE_READ_BIAS;
end else begin
index <= index + 1'b1;
access_addr <= w_group_base + index + 1'b1;
access_req <= 1'b1;
end
end
end
// =================================================
// READ BIAS
// =================================================
STATE_READ_BIAS: begin
if (access_ready) begin
bias_reg <= access_rdata;
state <= STATE_START_N;
end
end
// =================================================
// START NEURON
// =================================================
STATE_START_N: begin
neuron_start <= 1'b1;
state <= STATE_WAIT_N;
end
// =================================================
// WAIT NEURON
// =================================================
STATE_WAIT_N: begin
if (neuron_done) begin
y_reg[neuron_index] <= neuron_y;
if (neuron_index == n_neurons_real[NEURON_INDEX_WIDTH-1:0]-1'b1) begin
// Last neuron of the layer: done.
busy <= 1'b0;
done <= 1'b1;
state <= STATE_IDLE;
end else begin
// Advance to the next neuron: X stays
// in x_mem (shared), reload W and bias
// for neuron_index+1 from memory.
neuron_index <= neuron_index + 1'b1;
w_group_base <= w_group_base + n_inputs_real;
bias_group_addr <= bias_group_addr + 1'b1;
index <= 0;
access_addr <= w_group_base + n_inputs_real;
access_wr <= 1'b0;
access_req <= 1'b1;
state <= STATE_READ_W;
end
end
end
// =================================================
// DEFAULT
// =================================================
default: begin
state <= STATE_IDLE;
busy <= 1'b0;
end
endcase
end
end
endmodule
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