From 3f45cd2380acc4a036da4a9e26613a246aa30800 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Fri, 4 Oct 2019 22:38:46 -0400
Subject: [PATCH] Starts forming an Atari ST memory map.

---
 Machines/AtariST/AtariST.cpp      | 59 ++++++++++++++++++++++++++++---
 Machines/Utility/MemoryPacker.cpp |  5 +++
 Machines/Utility/MemoryPacker.hpp |  7 ++++
 3 files changed, 67 insertions(+), 4 deletions(-)

diff --git a/Machines/AtariST/AtariST.cpp b/Machines/AtariST/AtariST.cpp
index eff85308c..750ad2972 100644
--- a/Machines/AtariST/AtariST.cpp
+++ b/Machines/AtariST/AtariST.cpp
@@ -15,6 +15,9 @@
 #include "Video.hpp"
 #include "../../ClockReceiver/JustInTime.hpp"
 
+#include "../Utility/MemoryPacker.hpp"
+#include "../Utility/MemoryFuzzer.hpp"
+
 namespace Atari {
 namespace ST {
 
@@ -31,7 +34,8 @@ class ConcreteMachine:
 			mc68000_(*this) {
 			set_clock_rate(CLOCK_RATE);
 
-			ram_.resize(512 * 1024);
+			ram_.resize(512 * 512);
+			Memory::Fuzz(ram_);
 
 			std::vector<ROMMachine::ROM> rom_descriptions = {
 				{"AtariST", "the TOS ROM", "tos100.img", 192*1024, 0x1a586c64}
@@ -40,7 +44,7 @@ class ConcreteMachine:
 			if(!roms[0]) {
 				throw ROMMachine::Error::MissingROMs;
 			}
-			rom_ = *roms[0];
+			Memory::PackBigEndian16(*roms[0], rom_);
 		}
 
 		// MARK: CRTMachine::Machine
@@ -57,7 +61,54 @@ class ConcreteMachine:
 		}
 
 		// MARK: MC68000::BusHandler
+		using Microcycle = CPU::MC68000::Microcycle;
 		HalfCycles perform_bus_operation(const CPU::MC68000::Microcycle &cycle, int is_supervisor) {
+			// Advance time.
+			video_ += cycle.length;
+
+			// A null cycle leaves nothing else to do.
+			if(!(cycle.operation & (Microcycle::NewAddress | Microcycle::SameAddress))) return HalfCycles(0);
+
+			auto address = cycle.word_address();
+			uint16_t *memory;
+			if(address < 4) {
+				memory = rom_.data();
+			} else if(address < 0x700000) {
+				memory = ram_.data();
+				address &= ram_.size() - 1;
+				// TODO: align with the next access window.
+			} else if(address < 0x780000) {		// TOS 2.0+ address
+				memory = rom_.data();
+				address &= rom_.size() - 1;
+			} else if(address >= 0x7e0000 && address < 0x7f8000) {	// TOS 1.0 address
+				memory = rom_.data();
+				address &= rom_.size() - 1;
+			} else {
+				assert(false);
+			}
+
+			// If control has fallen through to here, the access is either a read from ROM, or a read or write to RAM.
+			switch(cycle.operation & (Microcycle::SelectWord | Microcycle::SelectByte | Microcycle::Read)) {
+				default:
+				break;
+
+				case Microcycle::SelectWord | Microcycle::Read:
+					cycle.value->full = memory[address];
+				break;
+				case Microcycle::SelectByte | Microcycle::Read:
+					cycle.value->halves.low = uint8_t(memory[address] >> cycle.byte_shift());
+				break;
+				case Microcycle::SelectWord:
+					memory[address] = cycle.value->full;
+				break;
+				case Microcycle::SelectByte:
+					memory[address] = uint16_t(
+						(cycle.value->halves.low << cycle.byte_shift()) |
+						(memory[address] & cycle.untouched_byte_mask())
+					);
+				break;
+			}
+
 			return HalfCycles(0);
 		}
 
@@ -65,8 +116,8 @@ class ConcreteMachine:
 		CPU::MC68000::Processor<ConcreteMachine, true> mc68000_;
 		JustInTimeActor<Video, HalfCycles> video_;
 
-		std::vector<uint8_t> ram_;
-		std::vector<uint8_t> rom_;
+		std::vector<uint16_t> ram_;
+		std::vector<uint16_t> rom_;
 
 };
 
diff --git a/Machines/Utility/MemoryPacker.cpp b/Machines/Utility/MemoryPacker.cpp
index 9630af259..101a68b5c 100644
--- a/Machines/Utility/MemoryPacker.cpp
+++ b/Machines/Utility/MemoryPacker.cpp
@@ -13,3 +13,8 @@ void Memory::PackBigEndian16(const std::vector<uint8_t> &source, uint16_t *targe
 		target[c >> 1] = uint16_t(source[c] << 8) | uint16_t(source[c+1]);
 	}
 }
+
+void Memory::PackBigEndian16(const std::vector<uint8_t> &source, std::vector<uint16_t> &target) {
+	target.resize(source.size() >> 1);
+	PackBigEndian16(source, target.data());
+}
diff --git a/Machines/Utility/MemoryPacker.hpp b/Machines/Utility/MemoryPacker.hpp
index 145191829..dbfd624a0 100644
--- a/Machines/Utility/MemoryPacker.hpp
+++ b/Machines/Utility/MemoryPacker.hpp
@@ -20,5 +20,12 @@ namespace Memory {
 */
 void PackBigEndian16(const std::vector<uint8_t> &source, uint16_t *target);
 
+/*!
+	Copies the bytes from @c source into @c target, interpreting them
+	as big-endian 16-bit data. @c target will be resized to the proper size
+	exactly to contain the contents of @c source.
+*/
+void PackBigEndian16(const std::vector<uint8_t> &source, std::vector<uint16_t> &target);
+
 }
 #endif /* MemoryPacker_hpp */