From 9d7985c1e1d151f5da89ed4ab02cdedd8ba40036 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sun, 26 Feb 2017 17:47:29 -0500
Subject: [PATCH] Added Super Chip emulation.

---
 Machines/Atari2600/Atari2600.cpp | 19 +++++++++++++++++--
 Machines/Atari2600/Atari2600.hpp |  5 +++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/Machines/Atari2600/Atari2600.cpp b/Machines/Atari2600/Atari2600.cpp
index 50745cb9b..054460596 100644
--- a/Machines/Atari2600/Atari2600.cpp
+++ b/Machines/Atari2600/Atari2600.cpp
@@ -87,8 +87,21 @@ unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uin
 		}
 
 		// check for a ROM read
-		if((address&0x1000) && isReadOperation(operation)) {
-			returnValue &= rom_pages_[(address >> 10)&3][address&1023];
+		uint16_t masked_address = address & 0x1fff;
+		if(address&0x1000)
+		{
+			if(isReadOperation(operation) && (!uses_superchip_ || masked_address > 0x10ff)) {
+				returnValue &= rom_pages_[(address >> 10)&3][address&1023];
+			}
+
+			// check for a Super Chip RAM access
+			if(uses_superchip_ && masked_address < 0x1100) {
+				if(masked_address < 0x1080) {
+					superchip_ram_[masked_address & 0x7f] = *value;
+				} else {
+					returnValue &= superchip_ram_[masked_address & 0x7f];
+				}
+			}
 		}
 
 		// check for a RAM access
@@ -263,6 +276,8 @@ void Machine::configure_as_target(const StaticAnalyser::Target &target)
 	rom_pages_[1] = &rom_[1024 & romMask];
 	rom_pages_[2] = &rom_[2048 & romMask];
 	rom_pages_[3] = &rom_[3072 & romMask];
+
+	uses_superchip_ = target.atari.uses_superchip;
 }
 
 #pragma mark - Audio and Video
diff --git a/Machines/Atari2600/Atari2600.hpp b/Machines/Atari2600/Atari2600.hpp
index f0970348e..c0ec017f1 100644
--- a/Machines/Atari2600/Atari2600.hpp
+++ b/Machines/Atari2600/Atari2600.hpp
@@ -56,9 +56,14 @@ class Machine:
 		virtual void crt_did_end_batch_of_frames(Outputs::CRT::CRT *crt, unsigned int number_of_frames, unsigned int number_of_unexpected_vertical_syncs);
 
 	private:
+		// ROM information
 		uint8_t *rom_, *rom_pages_[4];
 		size_t rom_size_;
 
+		// cartridge RAM expansion store
+		uint8_t superchip_ram_[128];
+		bool uses_superchip_;
+
 		// the RIOT and TIA
 		PIA mos6532_;
 		std::unique_ptr<TIA> tia_;