From 6572efe2a781f3c8f226f7d984a32161feccf74e Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 16 Sep 2021 08:24:52 -0400
Subject: [PATCH] Clarifies word addressing.

---
 Machines/Amiga/Blitter.cpp   |  2 +-
 Machines/Amiga/Chipset.cpp   | 22 ++++++++++------------
 Machines/Amiga/Chipset.hpp   |  2 +-
 Machines/Amiga/DMADevice.hpp | 18 +++++++++++++++---
 4 files changed, 27 insertions(+), 17 deletions(-)

diff --git a/Machines/Amiga/Blitter.cpp b/Machines/Amiga/Blitter.cpp
index 1e4d38a69..671398ba6 100644
--- a/Machines/Amiga/Blitter.cpp
+++ b/Machines/Amiga/Blitter.cpp
@@ -59,6 +59,6 @@ uint16_t Blitter::get_status() {
 }
 
 bool Blitter::advance() {
-	ram_[(pointer_[3] >> 1) & ram_mask_] = 0xffff;
+	ram_[pointer_[3] & ram_mask_] = 0xffff;
 	return false;
 }
diff --git a/Machines/Amiga/Chipset.cpp b/Machines/Amiga/Chipset.cpp
index 714e4a6a0..52c3213fc 100644
--- a/Machines/Amiga/Chipset.cpp
+++ b/Machines/Amiga/Chipset.cpp
@@ -32,11 +32,11 @@ template <DMAFlag... Flags> struct DMAMask: Mask<DMAFlag, Flags...> {};
 
 }
 
-Chipset::Chipset(uint16_t *ram, size_t size) :
-	blitter_(*this, ram, size),
-	bitplanes_(*this, ram, size),
-	copper_(*this, ram, size),
-	disk_(*this, ram, size),
+Chipset::Chipset(uint16_t *ram, size_t word_size) :
+	blitter_(*this, ram, word_size),
+	bitplanes_(*this, ram, word_size),
+	copper_(*this, ram, word_size),
+	disk_(*this, ram, word_size),
 	crt_(908, 4, Outputs::Display::Type::PAL50, Outputs::Display::InputDataType::Red4Green4Blue4) {
 }
 
@@ -231,7 +231,9 @@ template <int cycle> void Chipset::output() {
 				}
 
 				if(pixels_) {
-					// TODO: this is obviously nonsense.
+					// TODO: this is obviously nonsense. Probably do a table-based
+					// planar-to-chunky up front into 8-bit pockets, and just shift that.
+
 					pixels_[0] = palette_[
 						((current_bitplanes_[0]&1) << 0) |
 						((current_bitplanes_[1]&1) << 1) |
@@ -253,13 +255,13 @@ template <int cycle> void Chipset::output() {
 						((current_bitplanes_[3]&4) << 1) |
 						((current_bitplanes_[4]&4) << 2)
 					];
-					pixels_[3] = palette_[
+					pixels_[3] = 0;/*palette_[
 						((current_bitplanes_[0]&8) >> 3) |
 						((current_bitplanes_[1]&8) >> 2) |
 						((current_bitplanes_[2]&8) >> 1) |
 						((current_bitplanes_[3]&8) << 0) |
 						((current_bitplanes_[4]&8) << 1)
-					];
+					];*/
 
 					current_bitplanes_ >>= 4;
 					pixels_ += 4;
@@ -457,9 +459,6 @@ void Chipset::post_bitplanes(const BitplaneData &data) {
 	// TODO: should probably store for potential delay?
 	current_bitplanes_ = data;
 
-	if(data[0] || data[1]) {
-		printf("");
-	}
 //	current_bitplanes_[0] = 0xaaaa;
 //	current_bitplanes_[1] = 0x3333;
 //	current_bitplanes_[2] = 0x4444;
@@ -958,4 +957,3 @@ void Chipset::set_display_type(Outputs::Display::DisplayType type) {
 Outputs::Display::DisplayType Chipset::get_display_type() const {
 	return crt_.get_display_type();
 }
-
diff --git a/Machines/Amiga/Chipset.hpp b/Machines/Amiga/Chipset.hpp
index fd4f02a4b..3cb31818a 100644
--- a/Machines/Amiga/Chipset.hpp
+++ b/Machines/Amiga/Chipset.hpp
@@ -55,7 +55,7 @@ enum class DMAFlag: uint16_t {
 
 class Chipset {
 	public:
-		Chipset(uint16_t *ram, size_t size);
+		Chipset(uint16_t *ram, size_t word_size);
 
 		struct Changes {
 			int hsyncs = 0;
diff --git a/Machines/Amiga/DMADevice.hpp b/Machines/Amiga/DMADevice.hpp
index 9b1fe10ec..7a3da7d1c 100644
--- a/Machines/Amiga/DMADevice.hpp
+++ b/Machines/Amiga/DMADevice.hpp
@@ -19,8 +19,8 @@ class Chipset;
 
 class DMADeviceBase {
 	public:
-		DMADeviceBase(Chipset &chipset, uint16_t *ram, size_t size) :
-			chipset_(chipset), ram_(ram), ram_mask_(uint32_t((size - 1) >> 1)) {}
+		DMADeviceBase(Chipset &chipset, uint16_t *ram, size_t word_size) :
+			chipset_(chipset), ram_(ram), ram_mask_(uint32_t(word_size - 1)) {}
 
 	protected:
 		Chipset &chipset_;
@@ -36,11 +36,23 @@ template <size_t num_addresses> class DMADevice: public DMADeviceBase {
 		template <int id, int shift> void set_pointer(uint16_t value) {
 			static_assert(id < num_addresses);
 			static_assert(shift == 0 || shift == 16);
-			pointer_[id] = (pointer_[id] & (0xffff'0000 >> shift)) | uint32_t(value << shift);
+			byte_pointer_[id] = (byte_pointer_[id] & (0xffff'0000 >> shift)) | uint32_t(value << shift);
+			pointer_[id] = byte_pointer_[id] >> 1;
+		}
+
+		template <int id, int shift> uint16_t get_pointer() {
+			// Restore the original least-significant bit.
+			const uint32_t source = (pointer_[id] << 1) | (byte_pointer_[id] & 1);
+			return uint16_t(source >> shift);
 		}
 
 	protected:
+		// These are shifted right one to provide word-indexing pointers;
+		// subclasses should use e.g. ram_[pointer_[0] & ram_mask_] directly.
 		std::array<uint32_t, num_addresses> pointer_{};
+
+	private:
+		std::array<uint32_t, num_addresses> byte_pointer_{};
 };
 
 }