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perf(v2): word-level burst reads - 2.24-2.37x real wall-clock speedup (DEC-0015)

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Implements optimization #1 from the final benchmark campaign's own
recommendation: exploit psram_controller.v's already-implemented
page-mode support (confirmed present by direct inspection) by
fetching multiple bytes per real backend transaction instead of one
at a time.

Root cause addressed: int8_memory_access.v (the byte-level backend
prefetch_engine.v originally sat on) already converts every 8-bit
logical request into a full 16-bit PSRAM word access internally
(mem_addr <= addr >> 1), discarding half of every word it already
paid for. prefetch_engine.v/memory_manager.v now speak
memory_interface.v's own 16-bit word protocol directly, bypassing
int8_memory_access.v entirely - which remains untouched, still frozen
V1 (§1/§34); V2 simply reuses the lower layer of the same frozen
chain instead of the byte-splitting layer on top of it, the same
"reuse what fits" precedent slot_mem_arbiter.v already set.
slot_mem_arbiter.v and neural_multiprocessor.v widened to match
(lb_n/ub_n added, master port wired directly to memory_interface.v).

Real, measured results: M4's own single-job testbench shows 49-56%
fewer cycles (166->84, 446->204, 728->322, all still bit-exact). The
full final-benchmark campaign (24/24 workload/config combinations)
re-verified bit-exact with D-Stress's real wall-clock time (cycles /
real POST-P&R Fmax) improving 2.24-2.37x across every N_SLOTS tested,
against a small real Fmax cost (unchanged at N=1, -6.2% at N=2, -1.2%
at N=4).

tb_neural_multiprocessor.v (M8) and tb_benchmark_suite.v (final
campaign) needed zero changes - both treat neural_multiprocessor.v as
a black box. Only tb_memory_manager.v (M4, rewired to skip
int8_memory_access.v) and tb_dataflow_core.v (M7, behavioral model
widened to word-level) needed updates.

The "real parallel scaling is flat beyond N_SLOTS=2" finding (DEC-0014)
still holds - this optimization made the shared PSRAM port more
efficient per transaction, not multi-ported - so N_SLOTS=2 remains
the recommended default.

Logged: simulation/synthesis/timing/benchmark/decisions (DEC-0015)/
experiments (EXP-0015)/development.log.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013xXuuRUWZScuo1DeYJxs3v
This commit is contained in:
michele
2026-09-05 20:35:19 +02:00
co-authored by Claude Sonnet 5
parent 3cdaeaee35
commit e4a5540b6e
14 changed files with 489 additions and 168 deletions
Download Patch File Download Diff File Expand all files Collapse all files
hardware/v2/sim/tb_memory_manager.v
+14 -24
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@@ -50,11 +50,14 @@ module tb;
wire mm_result_valid, mm_result_ready;
wire signed [DATA_WIDTH-1:0] mm_result_data;
// ---- memory_manager <-> int8_memory_access (Memory Backend Interface) ----
// ---- memory_manager <-> memory_interface (word-level Memory
// Backend Interface, post-M10 DEC-0015 -- int8_memory_access is no
// longer in this datapath, see memory_manager.v's own header) ----
wire mem_req, mem_wr;
wire [ADDR_WIDTH-1:0] mem_addr;
wire signed [7:0] mem_wdata;
wire signed [7:0] mem_rdata;
wire [ADDR_WIDTH-1:0] mem_addr; // WORD address
wire [15:0] mem_wdata;
wire mem_lb_n, mem_ub_n;
wire [15:0] mem_rdata;
wire mem_ready;
memory_manager #(
@@ -67,6 +70,7 @@ module tb;
.input_data(mm_input_data), .weight_data(mm_weight_data), .tile_last(mm_tile_last),
.result_valid(mm_result_valid), .result_ready(mm_result_ready), .result_data(mm_result_data),
.mem_req(mem_req), .mem_wr(mem_wr), .mem_addr(mem_addr), .mem_wdata(mem_wdata),
.mem_lb_n(mem_lb_n), .mem_ub_n(mem_ub_n),
.mem_rdata(mem_rdata), .mem_ready(mem_ready)
);
@@ -105,23 +109,9 @@ module tb;
else if (job_valid_np && job_ready_np) job_valid_np <= 1'b0;
end
// ---- REAL, unmodified V1 backend chain ----
wire if_mem_req, if_mem_wr;
wire [ADDR_WIDTH-1:0] if_mem_addr;
wire [PSRAM_DATA_WIDTH-1:0] if_mem_wdata;
wire if_mem_lb_n, if_mem_ub_n;
wire [PSRAM_DATA_WIDTH-1:0] if_mem_rdata;
wire if_mem_ready;
int8_memory_access #(.ADDR_WIDTH(ADDR_WIDTH)) u_int8 (
.clk(clk), .rst(rst),
.req(mem_req), .wr(mem_wr), .addr(mem_addr), .wdata(mem_wdata),
.rdata(mem_rdata), .ready(mem_ready),
.mem_req(if_mem_req), .mem_wr(if_mem_wr), .mem_addr(if_mem_addr), .mem_wdata(if_mem_wdata),
.mem_lb_n(if_mem_lb_n), .mem_ub_n(if_mem_ub_n),
.mem_rdata(if_mem_rdata), .mem_ready(if_mem_ready)
);
// ---- REAL, unmodified V1 backend chain (memory_interface ->
// psram_controller; int8_memory_access no longer in this datapath,
// see memory_manager.v's own header, DEC-0015) ----
wire pc_mem_req, pc_mem_wr;
wire [ADDR_WIDTH-1:0] pc_mem_addr;
wire [PSRAM_DATA_WIDTH-1:0] pc_mem_wdata;
@@ -131,9 +121,9 @@ module tb;
memory_interface #(.ADDR_WIDTH(ADDR_WIDTH), .DATA_WIDTH(PSRAM_DATA_WIDTH)) u_memif (
.clk(clk), .rst(rst),
.req(if_mem_req), .wr(if_mem_wr), .addr(if_mem_addr), .wdata(if_mem_wdata),
.lb_n(if_mem_lb_n), .ub_n(if_mem_ub_n),
.rdata(if_mem_rdata), .ready(if_mem_ready),
.req(mem_req), .wr(mem_wr), .addr(mem_addr), .wdata(mem_wdata),
.lb_n(mem_lb_n), .ub_n(mem_ub_n),
.rdata(mem_rdata), .ready(mem_ready),
.mem_req(pc_mem_req), .mem_wr(pc_mem_wr), .mem_addr(pc_mem_addr), .mem_wdata(pc_mem_wdata),
.mem_lb_n(pc_mem_lb_n), .mem_ub_n(pc_mem_ub_n),
.mem_rdata(pc_mem_rdata), .mem_ready(pc_mem_ready)