Embraces a more communicative 68000 bus.

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -1464,6 +1464,7 @@
 		4BFF1D342233778C00838EA1 /* 68000.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = 68000.hpp; sourceTree = "<group>"; };
 		4BFF1D37223379D500838EA1 /* 68000Storage.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = 68000Storage.hpp; sourceTree = "<group>"; };
 		4BFF1D3822337B0300838EA1 /* 68000Storage.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = 68000Storage.cpp; sourceTree = "<group>"; };
+		4BFF1D3B2235714900838EA1 /* 68000Implementation.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = 68000Implementation.hpp; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -3216,6 +3217,7 @@
 			children = (
 				4BFF1D37223379D500838EA1 /* 68000Storage.hpp */,
 				4BFF1D3822337B0300838EA1 /* 68000Storage.cpp */,
+				4BFF1D3B2235714900838EA1 /* 68000Implementation.hpp */,
 			);
 			path = Implementation;
 			sourceTree = "<group>";

Processors/68000/68000.hpp

@@ -10,42 +10,95 @@
 #define MC68000_h
 
 #include <cstdint>
+#include <iostream>
 #include <vector>
 
 #include "../../ClockReceiver/ClockReceiver.hpp"
+#include "../RegisterSizes.hpp"
 
 namespace CPU {
 namespace MC68000 {
 
+/*!
+	A microcycle is an atomic unit of 68000 bus activity — it is a single item large enough
+	fully to specify a sequence of bus events that occur without any possible interruption.
+
+	Concretely, a standard read cycle breaks down into at least two microcycles:
+
+		1) a 5 half-cycle length microcycle in which the address strobe is signalled; and
+		2) a 3 half-cycle length microcycle in which at least one of the data strobes is
+		signalled, and the data bus is sampled.
+
+	That is, assuming DTack were signalled when microcycle (1) ended. If not then additional
+	wait state microcycles would fall between those two parts.
+
+	The 68000 data sheet defines when the address becomes valid during microcycle (1), and
+	when the address strobe is actually asserted. But those timings are fixed. So simply
+	telling you that this was a microcycle during which the address trobe was signalled is
+	sufficient fully to describe the bus activity.
+
+	(Aside: see the 68000 template's definition for options re: implicit DTack; if your
+	68000 owner can always predict exactly how long it will hold DTack following observation
+	of an address-strobing microcycle, it can just supply those periods for accounting and
+	avoid the runtime cost of actual DTack emulation. But such as the bus allows.)
+*/
 struct Microcycle {
-	enum Operation {
+	/*
-		Read16,
+		The operation code is a mask of all the signals that relevantly became active during
-		Write16,
+		this microcycle.
-		ReadHigh,
+	*/
-		ReadLow,
+	static const int Address	= 1 << 0;
-		WriteHigh,
+	static const int UpperData	= 1 << 1;
-		WriteLow,
+	static const int LowerData	= 1 << 2;
+	static const int ReadWrite 	= 1 << 3;	// Set = read; unset = write.
 
-		/// The data bus is not tristated, but no data request is made.
+	int operation = 0;
-		Idle,
+	HalfCycles length = HalfCycles(2);
 
-		/// No data bus interaction at all; bus is tristated.
+	/*!
-		None
+		For expediency, this provides a full 32-bit byte-resolution address — e.g.
-	};
+		if reading indirectly via an address register, this will indicate the full
+		value of the address register.
 
-	Operation operation = Operation::None;
+		The receiver should ignore bits 0 and 24+.
-	Cycles length = Cycles(2);
+	*/
-	uint32_t *address = nullptr;
+	const uint32_t *address = nullptr;
-	uint16_t *value = nullptr;
+	RegisterPair16 *value = nullptr;
 };
 
+/*!
+	This is the prototype for a 68000 bus handler; real bus handlers can descend from this
+	in order to get default implementations of any changes that may occur in the expected interface.
+*/
 class BusHandler {
 	public:
-		Cycles perform_machine_cycle(const Microcycle &cycle) {
+		static const int Data 			= 1 << 0;
-			return Cycles(0);
+		static const int Program		= 1 << 1;
+		static const int Supervisor		= 1 << 2;
+		static const int Interrupt		= Data | Program | Supervisor;
+
+		/*!
+			Provides the bus handler with a single Microcycle to 'perform', along with the
+			contents of the FC0, FC1 and FC2 lines by way of processor_status. The symbols
+			above, Data, Program, Supervisor and Interrupt can be used to help to decode the
+			processor status if desired; in summary:
+
+			If all three bits are set, this is an interrupt acknowledgement.
+
+			If the data bit is set, the 68000 is fetching data.
+
+			If the program bit is set, the 68000 is fetching instructions.
+
+			It the supervisor bit is set, the 68000 is currently in supervisor mode.
+
+			Neither program nor data being set has an undefined meaning. As does both program
+			and data being set, but this not being an interrupt.
+		*/
+		HalfCycles perform_bus_operation(const Microcycle &cycle, int processor_status) {
+			return HalfCycles(0);
 		}
 
-		void flush();
+		void flush() {}
 };
 
 #include "Implementation/68000Storage.hpp"
@@ -61,6 +114,8 @@ template <class T> class Processor: public ProcessorBase {
 		T &bus_handler_;
 };
 
+#include "Implementation/68000Implementation.hpp"
+
 }
 }
 

Processors/68000/Implementation/68000Implementation.hpp

@@ -0,0 +1,10 @@
+//
+//  68000Implementation.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 10/03/2019.
+//  Copyright © 2019 Thomas Harte. All rights reserved.
+//
+
+template <class T> void Processor<T>::run_for(Cycles cycles) {
+}

Processors/68000/Implementation/68000Storage.cpp

@@ -11,9 +11,14 @@
 using namespace CPU::MC68000;
 
 ProcessorStorage::ProcessorStorage() {
-	reset_program_ = assemble_program("n- n- n- n- n- nn nF nV nv np np");
+	reset_program_ = assemble_program("n- n- n- n- n- nn nF nf nV nv np np");
+
+	// Set initial state. Largely TODO.
+	active_program_ = reset_program_.data();
+	effective_address_ = 0;
 }
 
+// TODO: allow actions to be specified, of course.
 std::vector<ProcessorStorage::Step> ProcessorStorage::assemble_program(const char *access_pattern) {
 	std::vector<Step> steps;
 
@@ -22,24 +27,85 @@ std::vector<ProcessorStorage::Step> ProcessorStorage::assemble_program(const cha
 		Step step;
 
 		switch(*access_pattern) {
-			case ' ': break;	// Space acts as a no-op; it's for clarity only.
+			case '\t': case ' ': // White space acts as a no-op; it's for clarity only.
-
+				++access_pattern;
-			case 'n':	// Nothing occurs; supply as 'None'.
-				step.microcycle.operation = Microcycle::Operation::None;
 			break;
 
-			case '-':	// An idle cycle; distinct from a 'None'.
+			case 'n':	// This might be a plain NOP cycle, in which some internal calculation occurs,
-				step.microcycle.operation = Microcycle::Operation::Idle;
+						// or it might pair off with something afterwards.
+				switch(access_pattern[1]) {
+					default:	// This is probably a pure NOP; if what comes after this 'n' isn't actually
+								// valid, it should be caught in the outer switch the next time around the loop.
+						steps.push_back(step);
+						++access_pattern;
+					break;
+
+					case '-':	// This is two NOPs in a row.
+						steps.push_back(step);
+						steps.push_back(step);
+						access_pattern += 2;
+					break;
+
+					case 'F':	// Fetch SSP MSW.
+					case 'f':	// Fetch SSP LSW.
+						step.microcycle.length = HalfCycles(5);
+						step.microcycle.operation = Microcycle::Address | Microcycle::ReadWrite;
+						step.microcycle.address = &effective_address_;
+						step.microcycle.value = isupper(access_pattern[1]) ? &stack_pointers_[1].halves.high : &stack_pointers_[1].halves.low;
+						steps.push_back(step);
+
+						step.microcycle.length = HalfCycles(3);
+						step.microcycle.operation |= Microcycle::LowerData | Microcycle::UpperData;
+						step.action = Step::Action::IncrementEffectiveAddress;
+						steps.push_back(step);
+
+						access_pattern += 2;
+					break;
+
+					case 'V':	// Fetch exception vector low.
+					case 'v':	// Fetch exception vector high.
+						step.microcycle.length = HalfCycles(5);
+						step.microcycle.operation = Microcycle::Address | Microcycle::ReadWrite;
+						step.microcycle.address = &effective_address_;
+						step.microcycle.value = isupper(access_pattern[1]) ? &program_counter_.halves.high : &program_counter_.halves.low;
+						steps.push_back(step);
+
+						step.microcycle.length = HalfCycles(3);
+						step.microcycle.operation |= Microcycle::LowerData | Microcycle::UpperData;
+						step.action = Step::Action::IncrementEffectiveAddress;
+						steps.push_back(step);
+
+						access_pattern += 2;
+					break;
+
+					case 'p':	// Fetch from the program counter into the prefetch queue.
+						step.microcycle.length = HalfCycles(5);
+						step.microcycle.operation = Microcycle::Address | Microcycle::ReadWrite;
+						step.microcycle.address = &program_counter_.full;
+						step.microcycle.value = &prefetch_queue_[1];
+						step.action = Step::Action::AdvancePrefetch;
+						steps.push_back(step);
+
+						step.microcycle.length = HalfCycles(3);
+						step.microcycle.operation |= Microcycle::LowerData | Microcycle::UpperData;
+						step.action = Step::Action::IncrementProgramCounter;
+						steps.push_back(step);
+
+						access_pattern += 2;
+					break;
+				}
 			break;
 
-			default: assert(false);
+			default:
+				std::cerr << "MC68000 program builder; Unknown access type " << *access_pattern << std::endl;
+				assert(false);
 		}
-
-		steps.push_back(step);
-		++access_pattern;
 	}
 
-	// TODO: add actions, somehow.
+	// Add a final 'ScheduleNextProgram' sentinel.
+	Step end_program;
+	end_program.action = Step::Action::ScheduleNextProgram;
+	steps.push_back(end_program);
 
 	return steps;
 }

Processors/68000/Implementation/68000Storage.hpp

@@ -14,29 +14,55 @@ class ProcessorStorage {
 		ProcessorStorage();
 
 	protected:
-		uint32_t data_[8];
+		RegisterPair32 data_[8];
-		uint32_t address_[7];
+		RegisterPair32 address_[7];
-		uint32_t stack_pointers_[2];
+		RegisterPair32 stack_pointers_[2];	// [0] = user stack pointer; [1] = supervisor
-		uint32_t program_counter_;
+		RegisterPair32 program_counter_;
+
+		RegisterPair16 prefetch_queue_[2];
 
 		enum class State {
 			Reset,
 			Normal
 		};
 
+		// Generic sources and targets for memory operations.
+		uint32_t effective_address_;
+		RegisterPair32 bus_data_;
+
 		/*!
 			A step is a microcycle to perform plus an action to occur afterwards, if any.
 		*/
 		struct Step {
 			Microcycle microcycle;
 			enum class Action {
-				None
+				None,
-			} action_ = Action::None;
+
+				/// Performs effective_address_ += 2.
+				IncrementEffectiveAddress,
+
+				/// Performs program_counter_ += 2.
+				IncrementProgramCounter,
+
+				/// Copies prefetch_queue_[1] to prefetch_queue_[0].
+				AdvancePrefetch,
+
+				/*!
+					Terminates an atomic program; if nothing else is pending, schedules the next instruction.
+					This action is special in that it usurps any included microcycle. So any Step with this
+					as its action acts as an end-of-list sentinel.
+				*/
+				ScheduleNextProgram
+
+			} action = Action::None;
 		};
 
 		// Special programs.
 		std::vector<Step> reset_program_;
 
+		// Current program pointer.
+		Step *active_program_ = nullptr;
+
 	private:
 		enum class DataSize {
 			Byte, Word, LongWord
@@ -44,6 +70,46 @@ class ProcessorStorage {
 		enum class AddressingMode {
 		};
 
+		/*!
+			Produces a vector of Steps that implement the described program.
+
+			@param access_pattern A string describing the bus activity that occurs
+				during this program. This should follow the same general pattern as
+				those in yacht.txt; full description below.
+
+			@discussion
+			The access pattern is defined, as in yacht.txt, to be a string consisting
+			of the following discrete bus actions. Spaces are ignored.
+
+			* n: no operation; data bus is not used;
+			* -: idle state; data bus is not used but is also not available;
+			* p: program fetch; reads from the PC and adds two to it;
+			* W: write MSW of something onto the bus;
+			* w: write LSW of something onto the bus;
+			* R: read MSW of something from the bus;
+			* r: read LSW of soemthing from the bus;
+			* S: push the MSW of something onto the stack;
+			* s: push the LSW of something onto the stack;
+			* U: pop the MSW of something from the stack;
+			* u: pop the LSW of something from the stack;
+			* V: fetch a vector's MSW;
+			* v: fetch a vector's LSW;
+			* i: acquire interrupt vector in an IACK cycle;
+			* F: fetch the SSPs MSW;
+			* f: fetch the SSP's LSW.
+
+			Quite a lot of that is duplicative, implying both something about internal
+			state and something about what's observable on the bus, but it's helpful to
+			stick to that document's coding exactly for easier debugging.
+
+			p fetches will fill the prefetch queue, attaching an action to both the
+			step that precedes them and to themselves. The SSP fetches will go straight
+			to the SSP.
+
+			Other actions will by default act via effective_address_ and bus_data_.
+			The user should fill in the steps necessary to get data into or extract
+			data from those.
+		*/
 		std::vector<Step> assemble_program(const char *access_pattern);
 };
 

Processors/RegisterSizes.hpp

@@ -32,7 +32,7 @@ template <typename Full, typename Half> union RegisterPair {
 };
 
 typedef RegisterPair<uint16_t, uint8_t> RegisterPair16;
-typedef RegisterPair<uint32_t, uint16_t> RegisterPair32;
+typedef RegisterPair<uint32_t, RegisterPair16> RegisterPair32;
 
 }