From db82579d3c023c441c895d26d32de3fa039eafa4 Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Fri, 11 Nov 2022 16:28:55 -0800
Subject: Starting to write a real memory subsystem for biggolf.

---
 memory/dram.h | 50 ++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 46 insertions(+), 4 deletions(-)

(limited to 'memory/dram.h')

diff --git a/memory/dram.h b/memory/dram.h
index f59c7a6..31aea12 100644
--- a/memory/dram.h
+++ b/memory/dram.h
@@ -21,6 +21,8 @@ namespace memory {
 
         typedef std::array<line, PAGE_LINES> page;
 
+        const unsigned int latency;
+
         std::map<std::uint64_t, page> image;
 
         struct response {
@@ -38,11 +40,26 @@ namespace memory {
             infra::port<response> *responsep = nullptr;
         };
 
-        infra::port<command> commandp;
+        infra::port<command> *commandp = nullptr;
+
+        unsigned int progress = 0;
+        std::optional<command> current_command;
+
+        dram(unsigned int latency=0)
+            : latency(latency)
+        { }
 
         void clock() {
-            if (commandp.can_read()) {
-                const auto &c = commandp.peek();
+            if (!current_command.has_value() && commandp->can_read()) {
+                current_command = commandp->read();
+                progress = latency;
+            }
+            if (current_command.has_value()) {
+                if (progress) {
+                    --progress;
+                    return;
+                }
+                const auto &c = *current_command;
                 if (!c.responsep || c.responsep->can_write()) {
                     auto page_address = c.line_address >> PAGE_LINES_LOG2;
                     auto page_line = c.line_address & PAGE_LINE_OFFSET_MASK;
@@ -76,7 +93,7 @@ namespace memory {
                             c.responsep->write(std::move(r));
                         }
                     }
-                    commandp.discard();
+                    current_command.reset();
                 }
             }
         }
@@ -92,5 +109,30 @@ namespace memory {
                         return;
             }
         }
+
+        unsigned int fetch(std::uint64_t address) const {
+            auto page_address = address >> PAGE_LINES_LOG2;
+            if (auto i = image.find(page_address); i != image.end()) {
+                auto &page = i->second;
+                auto line_address = (address & PAGE_LINE_OFFSET_MASK) >> LINE_BYTES_LOG2;
+                auto &line = page[line_address];
+                auto word_address = address & LINE_BYTE_OFFSET_MASK;
+                return line[word_address];
+            }
+            return 0;
+        }
+
+        void store(std::uint64_t address, unsigned int value) {
+            auto page_address = address >> PAGE_LINES_LOG2;
+            auto [p, emplaced] = image.try_emplace(page_address);
+            auto &page = p->second;
+            if (emplaced)
+                for (unsigned int i = 0; i < PAGE_LINES; ++i)
+                    page[i].fill(0);
+            auto line_address = (address & PAGE_LINE_OFFSET_MASK) >> LINE_BYTES_LOG2;
+            auto &line = page[line_address];
+            auto word_address = address & LINE_BYTE_OFFSET_MASK;
+            line[word_address] = value;
+        }
     };
 }
-- 
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