From 3e0055737e6f8701425ca8e946387f6beac5eb76 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomasharte@google.com>
Date: Sat, 5 May 2018 19:32:08 -0400
Subject: [PATCH] Adds a genuine attempt to discern Pravetz disks from Apple.

---
 Analyser/Static/DiskII/StaticAnalyser.cpp | 99 ++++++++++++++++++++---
 1 file changed, 90 insertions(+), 9 deletions(-)

diff --git a/Analyser/Static/DiskII/StaticAnalyser.cpp b/Analyser/Static/DiskII/StaticAnalyser.cpp
index 2c0cc8aef..c60dfde4f 100644
--- a/Analyser/Static/DiskII/StaticAnalyser.cpp
+++ b/Analyser/Static/DiskII/StaticAnalyser.cpp
@@ -7,16 +7,48 @@
 //
 
 #include "StaticAnalyser.hpp"
+
 #include "../AppleII/Target.hpp"
+#include "../Oric/Target.hpp"
+#include "../Disassembler/6502.hpp"
+#include "../Disassembler/AddressMapper.hpp"
 
 #include "../../../Storage/Disk/Track/TrackSerialiser.hpp"
 #include "../../../Storage/Disk/Encodings/AppleGCR/SegmentParser.hpp"
 
+namespace {
+
+Analyser::Static::Target *AppleTarget(const Storage::Encodings::AppleGCR::Sector *sector_zero) {
+	using Target = Analyser::Static::AppleII::Target;
+	auto *target = new Target;
+	target->machine = Analyser::Machine::AppleII;
+
+	if(sector_zero && sector_zero->encoding == Storage::Encodings::AppleGCR::Sector::Encoding::FiveAndThree) {
+		target->disk_controller = Target::DiskController::ThirteenSector;
+	} else {
+		target->disk_controller = Target::DiskController::SixteenSector;
+	}
+
+	return target;
+}
+
+Analyser::Static::Target *OricTarget(const Storage::Encodings::AppleGCR::Sector *sector_zero) {
+	using Target = Analyser::Static::Oric::Target;
+	auto *target = new Target;
+	target->machine = Analyser::Machine::Oric;
+
+	// TODO: configure the Oric as a Pravetz 8D with 8DOS.
+
+	return target;
+}
+
+}
+
 Analyser::Static::TargetList Analyser::Static::DiskII::GetTargets(const Media &media, const std::string &file_name, TargetPlatform::IntType potential_platforms) {
 	// This analyser can comprehend disks only.
 	if(media.disks.empty()) return {};
 
-	// Grab track 0, sector 0.
+	// Grab track 0, sector 0: the boot sector.
 	auto track_zero = media.disks.front()->get_track_at_position(Storage::Disk::Track::Address(0, 0));
 	auto sector_map = Storage::Encodings::AppleGCR::sectors_from_segment(
 		Storage::Disk::track_serialisation(*track_zero, Storage::Time(1, 50000)));
@@ -28,15 +60,64 @@ Analyser::Static::TargetList Analyser::Static::DiskII::GetTargets(const Media &m
 			break;
 		}
 	}
-	
-	using Target = Analyser::Static::AppleII::Target;
-	auto target = std::unique_ptr<Target>(new Target);
-	target->machine = Machine::AppleII;
-	target->media = media;
-
-	target->disk_controller = Target::DiskController::SixteenSector;
 
+	// If there's no boot sector then if there are also no sectors at all,
+	// decline to nominate a machine. Otherwise go with an Apple as the default.
 	TargetList targets;
-	targets.push_back(std::move(target));
+	if(!sector_zero) {
+		if(sector_map.empty()) {
+			return targets;
+		} else {
+			targets.push_back(std::unique_ptr<Analyser::Static::Target>(AppleTarget(nullptr)));
+			return targets;
+		}
+	}
+
+	// If the boot sector looks like it's intended for the Oric, create an Oric.
+	// Otherwise go with the Apple II.
+
+	auto disassembly = Analyser::Static::MOS6502::Disassemble(sector_zero->data, Analyser::Static::Disassembler::OffsetMapper(0xb800), {0xb800});
+
+	bool did_read_shift_register = false;
+	bool is_oric = false;
+
+	// Look for a tight BPL loop reading the Oric's shift register address of 0x31c. The Apple II just has RAM there,
+	// so the probability of such a loop is infinitesimal.
+	for(const auto &instruction: disassembly.instructions_by_address) {
+		// Is this a read of the shift register?
+		if(
+			(
+				(instruction.second.operation == Analyser::Static::MOS6502::Instruction::LDA) ||
+				(instruction.second.operation == Analyser::Static::MOS6502::Instruction::LDX) ||
+				(instruction.second.operation == Analyser::Static::MOS6502::Instruction::LDY)
+			) &&
+			instruction.second.addressing_mode == Analyser::Static::MOS6502::Instruction::Absolute &&
+			instruction.second.address == 0x031c) {
+			did_read_shift_register = true;
+			continue;
+		}
+
+		if(did_read_shift_register) {
+			if(
+				instruction.second.operation == Analyser::Static::MOS6502::Instruction::BPL &&
+				instruction.second.address == 0xfb) {
+				is_oric = true;
+				break;
+			}
+
+			did_read_shift_register = false;
+		}
+	}
+
+	// Check also for calls into the 0x3xx page above 0x320, as that's where the Oric's boot ROM is.
+	for(const auto address: disassembly.outward_calls) {
+		is_oric |= address >= 0x320 && address < 0x400;
+	}
+
+	if(is_oric) {
+		targets.push_back(std::unique_ptr<Analyser::Static::Target>(OricTarget(sector_zero)));
+	} else {
+		targets.push_back(std::unique_ptr<Analyser::Static::Target>(AppleTarget(sector_zero)));
+	}
 	return targets;
 }