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FPGA-Neural/rtl/layer_sequencer.v
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michele 233d6ff7fb feat: complete Phase 5 multi-layer network (RUN_NETWORK) + fix STATUS race 
Wires the already-present layer_sequencer.v into the SPI stack:

- spi_engine.v: RUN_NETWORK opcode (0x23) + SET_BASE selectors for
  table_base/buf_a_base/buf_b_base; STATUS.busy/done extended to
  track the sequencer (seq_busy/seq_done) alongside neuron_memory
  directly, so done latches on the last layer only.
- spi_neuron_top.v: instantiates layer_sequencer, muxes
  neuron_memory's control inputs between it (while seq_busy) and
  spi_engine's direct-drive path (legacy single-layer mode), wires
  the sequencer's own RAM master to mem_arbiter's Port C.

Found and fixed a real race while writing the end-to-end test: STATUS's
sticky/clear-on-read done bit read its value live/combinationally
during transmission and cleared unconditionally on any STATUS read.
A done_event landing mid-transmission of a STATUS response byte could
be silently dropped -- the host would receive a stale byte while the
sticky bit was cleared regardless, hanging any host polling STATUS in
a loop. Present since Phase 4, not RUN_NETWORK-specific; only
surfaced under this test's continuous polling. Fixed by latching a
status_snapshot at opcode-accept time and gating the clear on what
was actually transmitted.

Tests: spi_engine_tb.v gains RUN_NETWORK/SET_BASE opcode tests (K/L);
new layer_sequencer_tb.v unit-tests the sequencer FSM directly
(descriptor table, ping-pong buffer addressing, byte-exact copy-out);
new spi_neuron_top_runnetwork_tb.v drives a real 2-layer network over
simulated SPI end to end (real neuron_memory + PSRAM, hand-computed
expected output) and confirms the legacy single-layer path still
works afterward. All existing testbenches still pass.
2026-09-02 19:47:36 +02:00

316 lines
11 KiB
Verilog
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`timescale 1ns/1ps
// ================================================================
// LAYER_SEQUENCER (Phase 5 - Multi-Layer Network)
//
// Chains up to N_LAYERS runs of a single, reused neuron_memory
// instance to execute a feedforward network of N_LAYERS dense
// layers, without touching neuron_memory.v or the validated compute
// core (neuron_parallel/mac8/mac_unit) at all.
//
// KEY DESIGN CHOICE: neuron_memory's N_INPUTS and N_NEURONS are both
// fixed at synthesis to the SAME value (this module's N_WIDTH
// parameter, e.g. 256). A logical layer with fewer real inputs or
// neurons than N_WIDTH is handled entirely by DATA convention, not
// RTL: the host zero-pads that layer's weight matrix beyond its
// real input count (so the extra MAC lanes contribute 0 regardless
// of input value) and its bias beyond its real neuron count. This
// sequencer then always reads/writes the FULL N_WIDTH-byte buffer
// for every layer transition -- it does not need to know any
// layer's "real" input/neuron count at all. Trade-off: a layer with
// few real inputs still takes as long as a full N_WIDTH-wide layer
// (wasted MAC cycles on zero-weighted padding); documented as a
// known Phase 7 (Optimization) follow-up, not solved here.
//
// Layer descriptor table (host-written via WRITE_RAM, read-only to
// this module): N_LAYERS entries of 6 bytes each, MSB-first,
// starting at `table_base`:
// w_base(3B), bias_addr(3B)
// Layer 0's input is the external `x_base` (same register used for
// single-layer/manual mode). Layer k>0's input is the ping-pong
// output buffer (`buf_a_base`/`buf_b_base`) written by layer k-1.
// The final layer's output is left both in neuron_memory's own
// y_bus (readable via the existing READ_OUTPUT opcode, unchanged)
// and in the ping-pong buffer it was copied to.
// ================================================================
module layer_sequencer #(
parameter ADDR_WIDTH = 22,
parameter DATA_WIDTH = 8,
parameter N_WIDTH = 256, // = neuron_memory's N_INPUTS = N_NEURONS
parameter N_LAYERS = 4
)(
input wire clk,
input wire rst,
// ------------------------------------------------------------
// Trigger (from spi_engine's RUN_NETWORK opcode)
// ------------------------------------------------------------
input wire run_start, // one-cycle pulse
input wire [7:0] run_num_layers, // 1..N_LAYERS
output reg seq_busy,
output reg seq_done, // one-cycle pulse, mirrors neuron_memory.done
// ------------------------------------------------------------
// Config registers (from spi_engine's SET_BASE)
// ------------------------------------------------------------
input wire [ADDR_WIDTH-1:0] x_base, // layer 0's external input
input wire [ADDR_WIDTH-1:0] table_base,
input wire [ADDR_WIDTH-1:0] buf_a_base,
input wire [ADDR_WIDTH-1:0] buf_b_base,
// ------------------------------------------------------------
// neuron_memory control (sequencer-owned; only meaningful while
// seq_busy -- the top level muxes these against spi_engine's
// own direct-drive outputs based on seq_busy)
// ------------------------------------------------------------
output reg [ADDR_WIDTH-1:0] nm_x_base,
output reg [ADDR_WIDTH-1:0] nm_w_base,
output reg [ADDR_WIDTH-1:0] nm_bias_addr,
output reg nm_start,
input wire nm_busy,
input wire nm_done, // one-cycle pulse
input wire signed [DATA_WIDTH*N_WIDTH-1:0] y_bus,
// ------------------------------------------------------------
// Byte-level RAM master port (own arbiter port)
// ------------------------------------------------------------
output reg ram_req,
output reg ram_wr,
output reg [ADDR_WIDTH-1:0] ram_addr,
output reg signed [7:0] ram_wdata,
input wire signed [7:0] ram_rdata,
input wire ram_ready
);
// ============================================================
// STATES
// ============================================================
localparam ST_IDLE = 4'd0;
localparam ST_READ_DESC = 4'd1;
localparam ST_READ_WAIT = 4'd2;
localparam ST_START_LAYER = 4'd3;
localparam ST_WAIT_LAYER = 4'd4;
localparam ST_COPY_ISSUE = 4'd5;
localparam ST_COPY_WAIT = 4'd6;
reg [3:0] state;
reg [7:0] layer_idx;
reg [7:0] num_layers_reg;
reg [ADDR_WIDTH-1:0] desc_table_addr;
reg [2:0] desc_byte_idx; // 0..5
reg [23:0] w_base_acc;
reg [23:0] bias_addr_acc;
reg cur_sel; // which ping-pong buffer to READ from for this layer (layer_idx>0)
reg write_sel; // which ping-pong buffer to WRITE this layer's output to
reg [$clog2(N_WIDTH+1)-1:0] copy_idx;
always @(posedge clk) begin
if (rst) begin
state <= ST_IDLE;
layer_idx <= 8'd0;
num_layers_reg <= 8'd0;
desc_table_addr <= {ADDR_WIDTH{1'b0}};
desc_byte_idx <= 3'd0;
w_base_acc <= 24'h0;
bias_addr_acc <= 24'h0;
cur_sel <= 1'b0;
write_sel <= 1'b0;
copy_idx <= 0;
nm_x_base <= {ADDR_WIDTH{1'b0}};
nm_w_base <= {ADDR_WIDTH{1'b0}};
nm_bias_addr <= {ADDR_WIDTH{1'b0}};
nm_start <= 1'b0;
ram_req <= 1'b0;
ram_wr <= 1'b0;
ram_addr <= {ADDR_WIDTH{1'b0}};
ram_wdata <= 8'sd0;
seq_busy <= 1'b0;
seq_done <= 1'b0;
end else begin
// --------------------------------------------------
// Default pulses
// --------------------------------------------------
nm_start <= 1'b0;
ram_req <= 1'b0;
seq_done <= 1'b0;
case (state)
// =================================================
// IDLE
// =================================================
ST_IDLE: begin
if (run_start) begin
seq_busy <= 1'b1;
layer_idx <= 8'd0;
num_layers_reg <= run_num_layers;
desc_table_addr <= table_base;
desc_byte_idx <= 3'd0;
write_sel <= 1'b0;
state <= ST_READ_DESC;
end
end
// =================================================
// READ DESCRIPTOR (6 bytes: w_base, bias_addr)
// =================================================
ST_READ_DESC: begin
ram_req <= 1'b1;
ram_wr <= 1'b0;
ram_addr <= desc_table_addr + desc_byte_idx;
state <= ST_READ_WAIT;
end
ST_READ_WAIT: begin
if (ram_ready) begin
case (desc_byte_idx)
3'd0: w_base_acc[23:16] <= ram_rdata;
3'd1: w_base_acc[15:8] <= ram_rdata;
3'd2: w_base_acc[7:0] <= ram_rdata;
3'd3: bias_addr_acc[23:16] <= ram_rdata;
3'd4: bias_addr_acc[15:8] <= ram_rdata;
3'd5: bias_addr_acc[7:0] <= ram_rdata;
endcase
if (desc_byte_idx == 3'd5) begin
desc_byte_idx <= 3'd0;
state <= ST_START_LAYER;
end else begin
desc_byte_idx <= desc_byte_idx + 3'd1;
state <= ST_READ_DESC;
end
end
end
// =================================================
// START LAYER
// =================================================
ST_START_LAYER: begin
nm_w_base <= w_base_acc[ADDR_WIDTH-1:0];
nm_bias_addr <= bias_addr_acc[ADDR_WIDTH-1:0];
nm_x_base <= (layer_idx == 8'd0)
? x_base
: (cur_sel ? buf_b_base : buf_a_base);
nm_start <= 1'b1;
state <= ST_WAIT_LAYER;
end
// =================================================
// WAIT FOR THIS LAYER TO FINISH
// =================================================
ST_WAIT_LAYER: begin
if (nm_done) begin
copy_idx <= 0;
state <= ST_COPY_ISSUE;
end
end
// =================================================
// COPY y_bus INTO THE PING-PONG OUTPUT BUFFER
// =================================================
ST_COPY_ISSUE: begin
ram_req <= 1'b1;
ram_wr <= 1'b1;
ram_addr <= (write_sel ? buf_b_base : buf_a_base) + copy_idx;
ram_wdata <= y_bus[copy_idx*DATA_WIDTH +: DATA_WIDTH];
state <= ST_COPY_WAIT;
end
ST_COPY_WAIT: begin
if (ram_ready) begin
if (copy_idx == N_WIDTH-1) begin
if (layer_idx == num_layers_reg - 8'd1) begin
// Last layer done.
seq_busy <= 1'b0;
seq_done <= 1'b1;
state <= ST_IDLE;
end else begin
// The buffer just written becomes
// the next layer's input.
cur_sel <= write_sel;
write_sel <= ~write_sel;
layer_idx <= layer_idx + 8'd1;
desc_table_addr <= desc_table_addr + 22'd6;
desc_byte_idx <= 3'd0;
state <= ST_READ_DESC;
end
end else begin
copy_idx <= copy_idx + 1'b1;
state <= ST_COPY_ISSUE;
end
end
end
default: begin
state <= ST_IDLE;
end
endcase
end
end
endmodule
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