From 93d2a612ee33a65441de993f4c6820ceb42ddf57 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Fri, 29 Jul 2022 16:33:46 -0400
Subject: [PATCH] Add an explicit flush-pipeline step; some tests now pass.

---
 Machines/Amiga/Blitter.cpp                    | 17 ++++++++++++-----
 Machines/Amiga/Blitter.hpp                    | 19 ++++++++-----------
 .../Clock SignalTests/AmigaBlitterTests.mm    |  1 +
 3 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/Machines/Amiga/Blitter.cpp b/Machines/Amiga/Blitter.cpp
index 312f28211..445ff9d07 100644
--- a/Machines/Amiga/Blitter.cpp
+++ b/Machines/Amiga/Blitter.cpp
@@ -344,7 +344,6 @@ bool Blitter::advance_dma() {
 		x_ = 0;
 		int loop_index_ = -1;
 		write_phase_ = WritePhase::Starting;
-		stopping_ = false;
 
 		while(true) {
 			const auto next = sequencer_.next();
@@ -362,7 +361,6 @@ bool Blitter::advance_dma() {
 					++y_;
 					if(y_ == height_) {
 						sequencer_.complete();
-						stopping_ = true;
 					}
 					pointer_[0] += modulos_[0] * channel_enables_[0] * direction_;
 					pointer_[1] += modulos_[1] * channel_enables_[1] * direction_;
@@ -389,10 +387,18 @@ bool Blitter::advance_dma() {
 				case Channel::None:
 				continue;
 				case Channel::Write: break;
+				case Channel::FlushPipeline:
+					// HACK. REMOVE ONCE NON-BLOCKING.
+					posit_interrupt(InterruptFlag::Blitter);
+					height_ = 0;
+					// END HACK.
+
+					if(write_phase_ == WritePhase::Full) {
+						ram_[write_address_ & ram_mask_] = write_value_;
+					}
+				return true;
 			}
 
-
-
 			a32_ = (a32_ << 16) | (a_data_ & transient_a_mask_);
 			b32_ = (b32_ << 16) | b_data_;
 
@@ -443,13 +449,14 @@ bool Blitter::advance_dma() {
 
 			switch(write_phase_) {
 				case WritePhase::Full:
-					ram_[write_address_ & ram_mask_] = output;
+					ram_[write_address_ & ram_mask_] = write_value_;
 					[[fallthrough]];
 
 				case WritePhase::Starting:
 					write_phase_ = WritePhase::Full;
 					write_address_ = pointer_[3];
 					write_value_ = output;
+					pointer_[3] += direction_;
 				continue;
 
 				default: break;
diff --git a/Machines/Amiga/Blitter.hpp b/Machines/Amiga/Blitter.hpp
index 8cb11a7c5..98e0e9e49 100644
--- a/Machines/Amiga/Blitter.hpp
+++ b/Machines/Amiga/Blitter.hpp
@@ -27,16 +27,14 @@ class BlitterSequencer {
 	public:
 		enum class Channel {
 			/// Tells the caller to calculate and load a new piece of output
-			/// into the output pipeline,
+			/// into the output pipeline.
 			///
-			/// If any inputs are enabled then a two-stage output pipeline applies:
-			/// if anything is already in the pipeline then it should now be written.
-			/// Then the new value should be placed into the pipeline ready for the
-			/// next write slot.
-			///
-			/// If the pipeline is empty, this acts the same as @c None, indicating
-			/// an unused DMA slot.
+			/// If any inputs are enabled then a one-slot output pipeline applies:
+			/// output will rest in the pipeline for one write phase before being written.
 			Write,
+			/// Indicates that a write should occur if anything is in the pipeline, otherwise
+			/// no activity should occur.
+			FlushPipeline,
 			/// The caller should read from channel C.
 			C,
 			/// The caller should read from channel B.
@@ -77,7 +75,7 @@ class BlitterSequencer {
 				default: break;
 
 				case Phase::Complete:
-				return std::make_pair(Channel::Write, loop_);
+				return std::make_pair(Channel::FlushPipeline, loop_);
 
 				case Phase::PauseAndComplete:
 					phase_ = Phase::Complete;
@@ -211,11 +209,10 @@ class Blitter: public DMADevice<4, 4> {
 		uint32_t write_address_ = 0xffff'ffff;
 		uint16_t write_value_ = 0;
 		enum WritePhase {
-			Starting, Full, Stopped
+			Starting, Full
 		} write_phase_;
 		int y_, x_;
 		uint16_t transient_a_mask_;
-		bool stopping_;
 };
 
 }
diff --git a/OSBindings/Mac/Clock SignalTests/AmigaBlitterTests.mm b/OSBindings/Mac/Clock SignalTests/AmigaBlitterTests.mm
index 159bb7cc7..e325c0de1 100644
--- a/OSBindings/Mac/Clock SignalTests/AmigaBlitterTests.mm	
+++ b/OSBindings/Mac/Clock SignalTests/AmigaBlitterTests.mm	
@@ -315,6 +315,7 @@ using WriteVector = std::vector<std::pair<uint32_t, uint16_t>>;
 				case Channel::C:	[components addObject:[NSString stringWithFormat:@"C%d", next.second]]; break;
 
 				case Channel::Write:
+				case Channel::FlushPipeline:
 					if(is_first_write) {
 						is_first_write = false;
 						[components addObject:@"-"];