From 4c9d6c5ee7aebb2f39367ae7689408a7fa862235 Mon Sep 17 00:00:00 2001
From: Paul Hollinsky <phollinsky@intrepidcs.com>
Date: Mon, 28 Feb 2022 01:55:31 -0500
Subject: [PATCH] Disk: NeoMemory: Cache last read sector for one second

This prevents constant re-reads if reading in small chunks
---
 disk/neomemorydiskreaddriver.cpp              | 49 +++++++++++--------
 include/icsneo/disk/neomemorydiskreaddriver.h |  6 +++
 2 files changed, 34 insertions(+), 21 deletions(-)

diff --git a/disk/neomemorydiskreaddriver.cpp b/disk/neomemorydiskreaddriver.cpp
index 22bb748..ef0d87d 100644
--- a/disk/neomemorydiskreaddriver.cpp
+++ b/disk/neomemorydiskreaddriver.cpp
@@ -12,30 +12,37 @@ optional<uint64_t> NeoMemoryDiskReadDriver::readLogicalDiskAligned(Communication
 	if(amount != SectorSize)
 		return 0;
 
-	const uint64_t currentSector = pos / SectorSize;
-	auto msg = com.waitForMessageSync([&currentSector, &com] {
-		return com.sendCommand(Command::NeoReadMemory, {
-			MemoryTypeSD,
-			uint8_t(currentSector & 0xFF),
-			uint8_t((currentSector >> 8) & 0xFF),
-			uint8_t((currentSector >> 16) & 0xFF),
-			uint8_t((currentSector >> 24) & 0xFF),
-			uint8_t(SectorSize & 0xFF),
-			uint8_t((SectorSize >> 8) & 0xFF),
-			uint8_t((SectorSize >> 16) & 0xFF),
-			uint8_t((SectorSize >> 24) & 0xFF)
-		});
-	}, NeoMemorySDRead, timeout);
+	if(cachePos != pos || std::chrono::steady_clock::now() > cachedAt + CacheTime) {
+		// The cache does not have this data, go get it
+		const uint64_t currentSector = pos / SectorSize;
+		auto msg = com.waitForMessageSync([&currentSector, &com] {
+			return com.sendCommand(Command::NeoReadMemory, {
+				MemoryTypeSD,
+				uint8_t(currentSector & 0xFF),
+				uint8_t((currentSector >> 8) & 0xFF),
+				uint8_t((currentSector >> 16) & 0xFF),
+				uint8_t((currentSector >> 24) & 0xFF),
+				uint8_t(SectorSize & 0xFF),
+				uint8_t((SectorSize >> 8) & 0xFF),
+				uint8_t((SectorSize >> 16) & 0xFF),
+				uint8_t((SectorSize >> 24) & 0xFF)
+			});
+		}, NeoMemorySDRead, timeout);
 
-	if(!msg)
-		return 0;
+		if(!msg)
+			return 0;
 
-	const auto sdmsg = std::dynamic_pointer_cast<NeoReadMemorySDMessage>(msg);
-	if(!sdmsg || sdmsg->data.size() != SectorSize) {
-		report(APIEvent::Type::PacketDecodingError, APIEvent::Severity::Error);
-		return nullopt;
+		const auto sdmsg = std::dynamic_pointer_cast<NeoReadMemorySDMessage>(msg);
+		if(!sdmsg || sdmsg->data.size() != SectorSize) {
+			report(APIEvent::Type::PacketDecodingError, APIEvent::Severity::Error);
+			return nullopt;
+		}
+
+		memcpy(cache.data(), sdmsg->data.data(), SectorSize);
+		cachedAt = std::chrono::steady_clock::now();
+		cachePos = pos;
 	}
 
-	memcpy(into, sdmsg->data.data(), SectorSize);
+	memcpy(into, cache.data(), SectorSize);
 	return SectorSize;
 }
\ No newline at end of file
diff --git a/include/icsneo/disk/neomemorydiskreaddriver.h b/include/icsneo/disk/neomemorydiskreaddriver.h
index 208b69d..2694a8f 100644
--- a/include/icsneo/disk/neomemorydiskreaddriver.h
+++ b/include/icsneo/disk/neomemorydiskreaddriver.h
@@ -5,6 +5,7 @@
 
 #include "icsneo/disk/diskreaddriver.h"
 #include <limits>
+#include <chrono>
 
 namespace icsneo {
 
@@ -26,6 +27,11 @@ public:
 
 private:
 	static constexpr const uint8_t MemoryTypeSD = 0x01; // Logical Disk
+	static constexpr const std::chrono::duration CacheTime = std::chrono::seconds(1);
+
+	std::array<uint8_t, SectorSize> cache;
+	uint64_t cachePos = 0;
+	std::chrono::time_point<std::chrono::steady_clock> cachedAt;
 
 	optional<uint64_t> readLogicalDiskAligned(Communication& com, device_eventhandler_t report,
 		uint64_t pos, uint8_t* into, uint64_t amount, std::chrono::milliseconds timeout) override;