fix: flatten LLR interface to packed vector for Yosys compatibility

Yosys doesn't support unpacked array ports. Changed llr_in/llr_input
from `logic signed [Q-1:0] llr[N]` to `logic [N*Q-1:0] llr` packed
vector. Also fixed blocking assignment in INIT loops (Verilator
BLKLOOPINIT requirement).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

verilog/rtl/ldpc_decoder_core.sv

@@ -30,8 +30,8 @@ module ldpc_decoder_core #(
     input  logic                    early_term_en,
     input  logic [4:0]              max_iter,
 
-    // Channel LLRs (loaded before start)
+    // Channel LLRs (loaded before start) - packed vector for Yosys compatibility
-    input  logic signed [Q-1:0]     llr_in [N],
+    input  logic [N*Q-1:0]          llr_in,
 
     // Status
     output logic                    busy,
@@ -208,14 +208,15 @@ module ldpc_decoder_core #(
 
                 INIT: begin
                     // Initialize beliefs from channel LLRs
+                    // Use blocking assignment for array in loop (Verilator requirement)
                     for (int j = 0; j < N; j++) begin
-                        beliefs[j] <= llr_in[j];
+                        beliefs[j] = $signed(llr_in[j*Q +: Q]);
                     end
                     // Zero all CN->VN messages
                     for (int r = 0; r < M_BASE; r++)
                         for (int c = 0; c < N_BASE; c++)
                             for (int z = 0; z < Z; z++)
-                                msg_cn2vn[r][c][z] <= {Q{1'b0}};
+                                msg_cn2vn[r][c][z] = {Q{1'b0}};
                     row_idx <= '0;
                     col_idx <= '0;
                     iter_cnt <= '0;

verilog/rtl/ldpc_decoder_top.sv

@@ -6,6 +6,7 @@
 //   - USE_POWER_PINS ifdef for Caravel power pass-through
 //   - 32-bit Wishbone address (lower 8 bits passed to wishbone_interface)
 //   - wb_sel_i byte selects accepted but unused (word-aligned access only)
+//   - LLR interface uses packed vector (Yosys compatibility)
 
 module ldpc_decoder_top #(
     parameter N_BASE    = 8,
@@ -13,7 +14,6 @@ module ldpc_decoder_top #(
     parameter Z         = 32,
     parameter N         = N_BASE * Z,
     parameter K         = Z,
-    parameter M         = M_BASE * Z,
     parameter Q         = 6,
     parameter MAX_ITER  = 30,
     parameter DC        = 8,
@@ -42,7 +42,7 @@ module ldpc_decoder_top #(
     logic        stat_busy;
     logic        stat_converged;
     logic [4:0]  stat_iter_used;
-    logic signed [Q-1:0] llr_input [N];
+    logic [N*Q-1:0] llr_input_flat;  // packed LLR vector
     logic [K-1:0]  decoded_bits;
     logic [7:0]    syndrome_weight;
 
@@ -55,7 +55,7 @@ module ldpc_decoder_top #(
         .ctrl_max_iter(ctrl_max_iter),
         .stat_busy(stat_busy), .stat_converged(stat_converged),
         .stat_iter_used(stat_iter_used),
-        .llr_input(llr_input), .decoded_bits(decoded_bits),
+        .llr_input(llr_input_flat), .decoded_bits(decoded_bits),
         .syndrome_weight(syndrome_weight), .irq_o(irq_o)
     );
 
@@ -65,7 +65,7 @@ module ldpc_decoder_top #(
     ) u_core (
         .clk(clk), .rst_n(rst_n),
         .start(ctrl_start), .early_term_en(ctrl_early_term),
-        .max_iter(ctrl_max_iter), .llr_in(llr_input),
+        .max_iter(ctrl_max_iter), .llr_in(llr_input_flat),
         .busy(stat_busy), .converged(stat_converged),
         .iter_used(stat_iter_used), .decoded_bits(decoded_bits),
         .syndrome_weight(syndrome_weight)

verilog/rtl/wishbone_interface.sv

@@ -32,7 +32,7 @@ module wishbone_interface #(
     input  logic                    stat_busy,
     input  logic                    stat_converged,
     input  logic [4:0]              stat_iter_used,
-    output logic signed [Q-1:0]     llr_input [N],
+    output logic [N*Q-1:0]          llr_input,     // packed LLR vector
     input  logic [K-1:0]            decoded_bits,
     input  logic [7:0]              syndrome_weight,
 
@@ -99,7 +99,7 @@ module wishbone_interface #(
                     int llr_idx;
                     llr_idx = word_idx * 5 + p;
                     if (llr_idx < N)
-                        llr_input[llr_idx] <= wb_dat_i[p*Q +: Q];
+                        llr_input[llr_idx*Q +: Q] <= wb_dat_i[p*Q +: Q];
                 end
             end
         end