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/cache.h | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 memory/cache.h

(limited to 'memory/cache.h')

diff --git a/memory/cache.h b/memory/cache.h
new file mode 100644
index 0000000..8554910
--- /dev/null
+++ b/memory/cache.h
@@ -0,0 +1,96 @@
+#pragma once
+
+#include <array>
+#include <cstdint>
+
+#include "memory/dram.h"
+#include "memory/line.h"
+
+namespace memory {
+    template<unsigned int SETS_LOG2, unsigned int WAYS> struct inline_cache {
+        static constexpr std::uint64_t SETS = 1 << SETS_LOG2;
+        static constexpr std::uint64_t LINE_SET_OFFSET_MASK = SETS - 1;
+
+        std::uint64_t last_serial = 0;
+
+        struct tag {
+            std::uint64_t serial = 0;
+            std::uint64_t line_address;
+            infra::transaction transaction;
+        };
+
+        typedef std::array<tag, WAYS> set_tags;
+        typedef std::array<line, WAYS> set_data;
+
+        std::array<set_tags, SETS> tags;
+        std::array<set_data, SETS> data;
+
+        void handle_response(const dram::response &r) {
+            auto set_address = r.line_address & LINE_SET_OFFSET_MASK;
+            auto &stags = tags[set_address];
+            auto &sdata = data[set_address];
+            for (unsigned int i = 0; i < WAYS; ++i) {
+                auto &stag = stags[i];
+                if (stag.serial && stag.line_address == r.line_address) {
+                    handle_response(r, stag, sdata[i]);
+                    return;
+                }
+            }
+            std::uint64_t min_serial = ~(std::uint64_t)0;
+            unsigned int victim;
+            for (unsigned int i = 0; i < WAYS; ++i) {
+                auto &stag = stags[i];
+                if (stag.serial < min_serial) {
+                    min_serial = stag.serial;
+                    victim = i;
+                }
+            }
+            handle_response(r, stags[victim], sdata[victim]);
+        }
+
+        void handle_response(const dram::response &r, tag &t, line &d) {
+            t.serial = ++last_serial;
+            t.line_address = r.line_address;
+            t.transaction = r.transaction;
+            d = r.data;
+        }
+
+        std::optional<tag> probe(std::uint64_t address) {
+            auto line_address = address >> LINE_BYTES_LOG2;
+            auto set_address = line_address & LINE_SET_OFFSET_MASK;
+            auto &stags = tags[set_address];
+            for (unsigned int i = 0; i < WAYS; ++i) {
+                auto &stag = stags[i];
+                if (stag.serial && stag.line_address == line_address)
+                    return stag;
+            }
+            return {};
+        }
+
+        std::optional<tag> fetchline(line &dst, std::uint64_t address) {
+            auto line_address = address >> LINE_BYTES_LOG2;
+            auto set_address = line_address & LINE_SET_OFFSET_MASK;
+            auto &stags = tags[set_address];
+            auto &sdata = data[set_address];
+            for (unsigned int i = 0; i < WAYS; ++i) {
+                auto &stag = stags[i];
+                if (stag.serial && stag.line_address == line_address) {
+                    stag.serial = ++last_serial;
+                    dst = sdata[i];
+                    return stag;
+                }
+            }
+            return {};
+        }
+
+        std::optional<tag> fetch(unsigned int &dst, std::uint64_t address) {
+            line data;
+            if (auto tag = fetchline(data, address); tag.has_value()) {
+                auto line_offset = address & LINE_BYTE_OFFSET_MASK;
+                dst = data[line_offset];
+                return tag;
+            }
+            return {};
+        }
+    };
+}
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