From d4b7d73fc4cfdd3ba4eced007b875a67940bf3fe Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sun, 7 Aug 2022 19:19:00 -0400
Subject: [PATCH] Further reduces lines to one access per slot, max.

---
 Machines/Amiga/Blitter.cpp | 22 +++++++++++++++++++---
 Machines/Amiga/Blitter.hpp |  1 +
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/Machines/Amiga/Blitter.cpp b/Machines/Amiga/Blitter.cpp
index dd55f01dd..e15cc4289 100644
--- a/Machines/Amiga/Blitter.cpp
+++ b/Machines/Amiga/Blitter.cpp
@@ -292,18 +292,30 @@ bool Blitter<record_bus>::advance_dma() {
 		// at https://github.com/niklasekstrom/blitter-subpixel-line/blob/master/Drawing%20lines%20using%20the%20Amiga%20blitter.pdf
 		//
 
+		//
+		// Caveat: I've no idea how the DMA access slots should be laid out for
+		// line drawing.
+		//
+
 		if(!busy_) {
 			error_ = int16_t(pointer_[0] << 1) >> 1;	// TODO: what happens if line_sign_ doesn't agree with this?
 			draw_ = true;
 			busy_ = true;
+			has_c_data_ = false;
 		}
 
+		bool did_output = false;
 		if(draw_) {
 			// TODO: patterned lines. Unclear what to do with the bit that comes out of b.
 			// Probably extend it to a full word?
-			c_data_ = ram_[pointer_[3] & ram_mask_];
-			if constexpr (record_bus) {
-				transactions_.emplace_back(Transaction::Type::ReadC, pointer_[3], c_data_);
+
+			if(!has_c_data_) {
+				has_c_data_ = true;
+				c_data_ = ram_[pointer_[3] & ram_mask_];
+				if constexpr (record_bus) {
+					transactions_.emplace_back(Transaction::Type::ReadC, pointer_[3], c_data_);
+				}
+				return true;
 			}
 
 			const uint16_t output =
@@ -311,6 +323,8 @@ bool Blitter<record_bus>::advance_dma() {
 			ram_[pointer_[3] & ram_mask_] = output;
 			not_zero_flag_ |= output;
 			draw_ &= !one_dot_;
+			has_c_data_ = false;
+			did_output = true;
 			if constexpr (record_bus) {
 				transactions_.emplace_back(Transaction::Type::WriteFromPipeline, pointer_[3], output);
 			}
@@ -361,6 +375,8 @@ bool Blitter<record_bus>::advance_dma() {
 			busy_ = false;
 			posit_interrupt(InterruptFlag::Blitter);
 		}
+
+		return did_output;
 	} else {
 		// Copy mode.
 		if(!busy_) {
diff --git a/Machines/Amiga/Blitter.hpp b/Machines/Amiga/Blitter.hpp
index 34ad82c89..720202004 100644
--- a/Machines/Amiga/Blitter.hpp
+++ b/Machines/Amiga/Blitter.hpp
@@ -263,6 +263,7 @@ template <bool record_bus = false> class Blitter: public DMADevice<4, 4> {
 
 		int error_ = 0;
 		bool draw_ = false;
+		bool has_c_data_ = false;
 
 		void add_modulos();
 		std::vector<Transaction> transactions_;