From 5d95607192380be5cc62592efac52814a0e090df Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Tue, 23 Mar 2021 12:22:38 -0700
Subject: Initial commit.

---
 bin2bcd.sv | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100644 bin2bcd.sv

(limited to 'bin2bcd.sv')

diff --git a/bin2bcd.sv b/bin2bcd.sv
new file mode 100644
index 0000000..80dc633
--- /dev/null
+++ b/bin2bcd.sv
@@ -0,0 +1,98 @@
+module bin2bcd
+    #(  BITS = 8
+    ,   BASE = 10
+    )
+    (   input   bit clk
+    ,   input   bit reset
+
+    ,   output  bit             bin_ready
+    ,   input   bit             bin_valid   `define bin_valid $past(bin_valid)
+    ,   input   bit [BITS-1:0]  bin_data    `define bin_data $past(bin_data)
+
+    ,   input   bit                             bcd_ready   `define bcd_ready $past(bcd_ready)
+    ,   output  bit                             bcd_valid
+    ,   output  bit [DIGITS-1:0][BASE_BITS-1:0] bcd_data
+    );
+
+// FIXME I don't think this works for odd bases
+
+localparam BASE_BITS = $clog2(BASE);
+localparam SLACK = (1 << BASE_BITS) - BASE;
+localparam DIGITS = $rtoi($ceil($ln(1 << BITS) / $ln(BASE)));
+localparam CARRY_TEST = $rtoi($ceil($itor(BASE) / 2));
+localparam CARRY_ADD = $rtoi($ceil($itor(SLACK) / 2));
+
+`ifdef DEBUG_BIN2BCD
+
+initial $display("%d BITS", BITS);
+initial $display("%d BASE", BASE);
+initial $display("%d BASE_BITS", BASE_BITS);
+initial $display("%d SLACK", SLACK);
+initial $display("%d DIGITS", DIGITS);
+initial $display("%d CARRY_TEST", CARRY_TEST);
+initial $display("%d CARRY_ADD", CARRY_ADD);
+
+initial for(int i = 0; i < BASE; i = i + 1) begin
+    // verilator lint_off WIDTH
+    automatic bit [BASE_BITS-1:0] n = i;
+    automatic bit [BASE_BITS-1:0] a = n >= CARRY_TEST ? CARRY_ADD : 0;
+    automatic bit [BASE_BITS-1:0] s = n + a;
+    // verilator lint_on WIDTH
+    automatic bit c;
+    automatic bit [BASE_BITS-1:0] d;
+    {c, d} = {s, 1'b0};
+    $display("\t\t(%x + %x => %x) * 2 => %x:%x", n, a, s, c, d);
+end
+
+`endif
+
+bit bin_b_valid;
+bit [BITS-1:0] bin_b_data;
+
+bit [DIGITS-1:0][BASE_BITS-1:0] bcd;;
+
+bit [$clog2(BITS):0] work;
+
+always_ff @(posedge clk) begin
+    if (reset) begin
+        bin_ready = 0;
+        bcd_valid = 0;
+        bin_b_valid = 0;
+    end else begin
+        if (bin_ready && `bin_valid) begin
+            bin_b_valid = 1;
+            bin_b_data = `bin_data;
+            bcd = 0;
+            work = BITS;
+            for (int i = BITS; i > 0; i = i - 1) begin
+                if (bin_b_data[BITS-1]) break;
+                bin_b_data = { bin_b_data[BITS-2:0], 1'b0 };
+                work = work - 1;
+            end
+        end
+
+        if (bin_b_valid && work != 0) begin
+            for (int i = 0; i < DIGITS; i = i + 1)
+                // verilator lint_off WIDTH
+                if (bcd[i] >= CARRY_TEST) bcd[i] = bcd[i] + CARRY_ADD;
+                // verilator lint_on WIDTH
+            for (int i = DIGITS - 1; i > 0; i = i - 1)
+                bcd[i] = { bcd[i][BASE_BITS-2:0], bcd[i-1][BASE_BITS-1] };
+            bcd[0] = { bcd[0][BASE_BITS-2:0], bin_b_data[BITS-1] };
+            bin_b_data = { bin_b_data[BITS-2:0], 1'b0 };
+
+            work = work - 1;
+        end
+
+        if (`bcd_ready) bcd_valid = 0;
+        if (!bcd_valid && bin_b_valid && work == 0) begin
+            bcd_valid = 1;
+            bcd_data = bcd;
+            bin_b_valid = 0;
+        end
+
+        bin_ready = !bin_b_valid;
+    end
+end
+
+endmodule
-- 
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