From fce46a9a7bb2fe2a9b3addca0f488931b9e231ff Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Sun, 13 Mar 2022 16:50:34 -0700
Subject: Add memory arbiter and broadcast in between command UART and DRAM.

---
 hdl/mem_arbiter.sv | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 hdl/mem_arbiter.sv

(limited to 'hdl/mem_arbiter.sv')

diff --git a/hdl/mem_arbiter.sv b/hdl/mem_arbiter.sv
new file mode 100644
index 0000000..ba3bd7d
--- /dev/null
+++ b/hdl/mem_arbiter.sv
@@ -0,0 +1,79 @@
+`include "defs.svh"
+
+module mem_arbiter
+    (   input   bit             clock
+    ,   input   bit             reset
+
+    ,   output  bit             command_ready
+    ,   input   bit             command_valid
+    ,   input   ram_command_t   command_data
+
+    ,   output  bit             [`NUM_PDPS-1:0] pdp_ready
+    ,   input   bit             [`NUM_PDPS-1:0] pdp_valid
+    ,   input   pdp_command_t   [`NUM_PDPS-1:0] pdp_data
+
+    ,   input   bit             ram_ready
+    ,   output  bit             ram_valid
+    ,   output  ram_command_t   ram_data
+    );
+
+    bit             [`NUM_PDPS:0]   hold_valid;
+    ram_command_t   [`NUM_PDPS:0]   hold_data;
+
+    bit [$clog2(`NUM_PDPS+1):0] selector;
+
+    always @(posedge clock) begin
+        if (reset) begin
+            command_ready = 0;
+            for (int i = 0; i < `NUM_PDPS; ++i)
+                pdp_ready[i] = 0;
+            ram_valid = 0;
+            for (int i = 0; i < `NUM_PDPS+1; ++i)
+                hold_valid[i] = 0;
+            selector = 0;
+        end else begin
+            automatic bit ram_was_valid = ram_valid;
+
+            if (ram_ready) ram_valid = 0;
+
+            if (command_ready && command_valid) begin
+                hold_valid[0] = 1;
+                hold_data[0] = command_data;
+                hold_data[0].tag = 0;
+            end
+            for (int i = 0; i < `NUM_PDPS; ++i) begin
+                if (pdp_ready[i] && pdp_valid[i]) begin
+                    hold_valid[i+1] = 1;
+                    hold_data[i+1].address[`RAM_ADDRESS_BITS-1:`PDP_ADDRESS_BITS] = i;
+                    hold_data[i+1].address[`PDP_ADDRESS_BITS-1:$clog2(`RAM_LINE_WORDS)] = pdp_data[i].address;
+                    hold_data[i+1].write = pdp_data[i].write;
+                    hold_data[i+1].data = pdp_data[i].data;
+                    hold_data[i+1].mask = pdp_data[i].mask;
+                    hold_data[i+1].tag = i+1;
+                end
+            end
+
+            for (int i = 0; i < `NUM_PDPS+1; ++i) begin
+                automatic int j = selector + i;
+                if (j > `NUM_PDPS) j = j - `NUM_PDPS-1;
+                if (!ram_valid && hold_valid[j]) begin
+                    ram_valid = 1;
+                    ram_data = hold_data[j];
+                    hold_valid[j] = 0;
+                end
+            end
+
+            if (ram_valid && !ram_was_valid) begin
+                if (selector == `NUM_PDPS)
+                    selector = 0;
+                else
+                    ++selector;
+            end
+
+            command_ready = !hold_valid[0];
+            for (int i = 0; i < `NUM_PDPS; ++i)
+                pdp_ready[i] = !hold_valid[i+1];
+        end
+    end
+
+endmodule
-- 
cgit v1.2.3