Split the post-route table into tx and rx

README.md

@@ -60,12 +60,12 @@ Properties proven in formal:
 Every module builds from the top-level Makefile.
 
 ```
-make MOD=uart_rx         # run a module's testbench
-make wave MOD=uart_rx    # run the testbench and open the waveform in Surfer
-make formal MOD=uart_rx  # run the module's SymbiYosys proof
-make cocotb              # run the top-level cocotb loopback test
-./synth_stats.sh uart    # report a module's synthesis cost
-./fmax.sh uart tt_uart clk        # fmax and utilization
+make MOD=uart_rx                    # run a module's testbench
+make wave MOD=uart_rx               # run the testbench and open the waveform in Surfer
+make formal MOD=uart_rx             # run the module's SymbiYosys proof
+make cocotb                         # run the top-level cocotb loopback test
+./synth_stats.sh uart               # report a module's synthesis cost
+./fmax.sh uart_tx tt_uart_tx clk    # fmax and utilization
 ```
 
 ## Synthesis
@@ -82,11 +82,12 @@ Synthesized for the Digilent Basys 3 (Xilinx Artix-7).
 
 ### Post-route timing
 
-`fmax.sh` places and routes the core in a registered-boundary harness and reports the maximum clock frequency. The frequency comes from the open nextpnr-xilinx flow, which is experimental and not vendor signed timing analysis.
+`fmax.sh` places and routes each module in a registered-boundary harness and reports the maximum clock frequency. This data relies on the experimental nextpnr-xilinx open-source toolchain, meaning frequencies are unverified and lack vendor-signed timing analysis.
 
 | Module | LUTs | Flip-flops | Block RAMs | Fmax |
 |--------|------|------------|------------|------|
-| `uart` | 63 | 60 | 0 | 277 MHz |
+| `uart_tx` | 25 | 26 | 0 | 316 MHz |
+| `uart_rx` | 32 | 34 | 0 | 296 MHz |
 
 ### Tool versions
 

fmax/tt_uart_rx.sv

@@ -0,0 +1,26 @@
+// UART RX harness
+module tt_uart_rx (
+    input  logic clk,
+    input  logic rst_n,
+    input  logic si,
+    output logic so
+);
+  localparam int NOUT = 10;
+
+  logic rx_serial_r;
+  logic [NOUT-1:0] out_w, out_r;
+
+  always_ff @(posedge clk) rx_serial_r <= si;
+
+  uart_rx dut (
+      .clk     (clk),
+      .rst_n   (rst_n),
+      .rx_serial(rx_serial_r),
+      .rx_data (out_w[7:0]),
+      .rx_valid(out_w[8]),
+      .rx_error(out_w[9])
+  );
+
+  always_ff @(posedge clk) out_r <= out_w;
+  always_ff @(posedge clk) so <= ^out_r;
+endmodule

fmax/tt_uart.sv → fmax/tt_uart_tx.sv

@@ -1,29 +1,25 @@
-// UART timing harness
-module tt_uart (
+// UART TX harness
+module tt_uart_tx (
     input  logic clk,
     input  logic rst_n,
     input  logic si,
     output logic so
 );
-  localparam int NIN = 10;
-  localparam int NOUT = 12;
+  localparam int NIN = 9;
+  localparam int NOUT = 2;
 
   logic [NIN-1:0] in_r;
   logic [NOUT-1:0] out_w, out_r;
 
   always_ff @(posedge clk) in_r <= {in_r[NIN-2:0], si};
 
-  uart dut (
+  uart_tx dut (
       .clk      (clk),
       .rst_n    (rst_n),
       .tx_data  (in_r[7:0]),
       .tx_valid (in_r[8]),
       .tx_ready (out_w[0]),
-      .tx_serial(out_w[1]),
-      .rx_serial(in_r[9]),
-      .rx_data  (out_w[9:2]),
-      .rx_valid (out_w[10]),
-      .rx_error (out_w[11])
+      .tx_serial(out_w[1])
   );
 
   always_ff @(posedge clk) out_r <= out_w;