From c9bf2dda164ff7b64d30f45862fa88a272017397 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Tue, 2 Nov 2021 18:18:59 -0700
Subject: [PATCH] Attempt implementation of disk sync.

---
 Machines/Amiga/Chipset.cpp |  2 +-
 Machines/Amiga/Chipset.hpp | 10 +++++++++-
 Machines/Amiga/Disk.cpp    | 25 ++++++++++++++++---------
 3 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/Machines/Amiga/Chipset.cpp b/Machines/Amiga/Chipset.cpp
index fae7212c5..d244c673c 100644
--- a/Machines/Amiga/Chipset.cpp
+++ b/Machines/Amiga/Chipset.cpp
@@ -670,6 +670,7 @@ void Chipset::perform(const CPU::MC68000::Microcycle &cycle) {
 			ApplySetClear(paula_disk_control_, 0x7fff);
 
 			disk_controller_.set_control(paula_disk_control_);
+			disk_.set_control(paula_disk_control_);
 			// TODO: should also post to Paula.
 		break;
 		case Read(0x010):		// ADKCONR
@@ -679,7 +680,6 @@ void Chipset::perform(const CPU::MC68000::Microcycle &cycle) {
 
 		case Write(0x07e):		// DSKSYNC
 			disk_controller_.set_sync_word(cycle.value16());
-			assert(false);	// Not fully implemented.
 		break;
 		case Read(0x01a):		// DSKBYTR
 			LOG("TODO: disk status");
diff --git a/Machines/Amiga/Chipset.hpp b/Machines/Amiga/Chipset.hpp
index 88903848e..7fbee2ca3 100644
--- a/Machines/Amiga/Chipset.hpp
+++ b/Machines/Amiga/Chipset.hpp
@@ -383,7 +383,8 @@ class Chipset: private ClockingHint::Observer {
 			public:
 				using DMADevice::DMADevice;
 
-				void set_length(uint16_t value);
+				void set_length(uint16_t);
+				void set_control(uint16_t);
 				bool advance();
 
 				void enqueue(uint16_t value, bool matches_sync);
@@ -393,9 +394,16 @@ class Chipset: private ClockingHint::Observer {
 				bool dma_enable_ = false;
 				bool write_ = false;
 				uint16_t last_set_length_ = 0;
+				bool sync_with_word_ = false;
 
 				std::array<uint16_t, 4> buffer_;
 				size_t buffer_read_ = 0, buffer_write_ = 0;
+
+				enum class State {
+					Inactive,
+					WaitingForSync,
+					Reading,
+				} state_ = State::Inactive;
 		} disk_;
 
 		class DiskController: public Storage::Disk::Controller {
diff --git a/Machines/Amiga/Disk.cpp b/Machines/Amiga/Disk.cpp
index 4e3eb074b..7e18ff580 100644
--- a/Machines/Amiga/Disk.cpp
+++ b/Machines/Amiga/Disk.cpp
@@ -16,18 +16,22 @@ using namespace Amiga;
 // MARK: - Disk DMA.
 
 void Chipset::DiskDMA::enqueue(uint16_t value, bool matches_sync) {
-	if(matches_sync) {
-		// TODO: start buffering from the next word onwards if
-		// syncing is enabled.
+	if(matches_sync && state_ == State::WaitingForSync) {
+		state_ = State::Reading;
+		return;
 	}
 
-//	LOG("In: " << buffer_write_);
-
-	buffer_[buffer_write_ & 3] = value;
-	if(buffer_write_ == buffer_read_ + 4) {
-		++buffer_read_;
+	if(state_ == State::Reading) {
+		buffer_[buffer_write_ & 3] = value;
+		if(buffer_write_ == buffer_read_ + 4) {
+			++buffer_read_;
+		}
+		++buffer_write_;
 	}
-	++buffer_write_;
+}
+
+void Chipset::DiskDMA::set_control(uint16_t control) {
+	sync_with_word_ = control & 0x400;
 }
 
 void Chipset::DiskDMA::set_length(uint16_t value) {
@@ -40,6 +44,8 @@ void Chipset::DiskDMA::set_length(uint16_t value) {
 		if(dma_enable_) {
 			LOG("Disk DMA " << (write_ ? "write" : "read") << " of " << length_ << " to " << PADHEX(8) << pointer_[0]);
 		}
+
+		state_ = sync_with_word_ ? State::WaitingForSync : State::Reading;
 	}
 
 	last_set_length_ = value;
@@ -57,6 +63,7 @@ bool Chipset::DiskDMA::advance() {
 
 			if(!length_) {
 				chipset_.posit_interrupt(InterruptFlag::DiskBlock);
+				state_ = State::Inactive;
 			}
 
 			return true;