Seemingly navigate I2C correctly.

Components/I2C/I2C.cpp

@@ -24,7 +24,7 @@ void Bus::set_data(bool pulled) {
 bool Bus::data() {
 	bool result = data_;
 	if(peripheral_bits_) {
-		result |= !(peripheral_response_ & 0x200);
+		result |= !(peripheral_response_ & 0x80);
 	}
 	return result;
 }
@@ -41,34 +41,51 @@ void Bus::set_clock_data(bool clock_pulled, bool data_pulled) {
 		return;
 	}
 
+	const bool prior_clock = clock_;
 	const bool prior_data = data_;
 	clock_ = clock_pulled;
 	data_ = data_pulled;
 
-	if(clock_) {
+	if(peripheral_bits_) {
+		// Trailing edge of clock => bit has been consumed.
+		if(!prior_clock && clock_) {
+			logger.info().append("<< %d", (peripheral_response_ >> 7) & 1);
+			--peripheral_bits_;
+			peripheral_response_ <<= 1;
+
+			if(!peripheral_bits_) {
+				signal(Event::FinishedOutput);
+			}
+		}
 		return;
 	}
 
-	if(prior_data != data_) {
+	if(!clock_ && prior_data != data_) {
+		// Data transition outside of a clock cycle => start or stop.
+		in_bit_ = false;
 		if(data_) {
-//			logger.info().append("S");
+			logger.info().append("S");
 			signal(Event::Start);
 		} else {
-//			logger.info().append("P");
+			logger.info().append("W");
 			signal(Event::Stop);
 		}
-	} else {
+	} else if(clock_ != prior_clock) {
-		if(peripheral_bits_) {
+		// Bits: wait until the falling edge of the cycle.
-			--peripheral_bits_;
+		if(!clock_) {
-			peripheral_response_ <<= 1;
+			// Rising edge: clock period begins.
-		}
+			in_bit_ = true;
+		} else if(in_bit_) {
+			// Falling edge: clock period ends (assuming it began; otherwise this is prep, post-start bit).
+			in_bit_ = false;
 
-		if(data_) {
+			if(data_) {
-//			logger.info().append("0");
+				logger.info().append("0");
-			signal(Event::Zero);
+				signal(Event::Zero);
-		} else {
+			} else {
-//			logger.info().append("1");
+				logger.info().append("1");
-			signal(Event::One);
+				signal(Event::One);
+			}
 		}
 	}
 }
@@ -82,7 +99,7 @@ void Bus::signal(Event event) {
 	const auto acknowledge = [&]() {
 		// Post an acknowledgement bit.
 		peripheral_response_ = 0;
-		peripheral_bits_ = 2;
+		peripheral_bits_ = 1;
 	};
 
 	const auto set_state = [&](State state) {
@@ -93,11 +110,10 @@ void Bus::signal(Event event) {
 
 	const auto enqueue = [&](std::optional<uint8_t> next) {
 		if(next) {
-			peripheral_response_ = static_cast<uint16_t>((*next) << 1);
+			peripheral_response_ = static_cast<uint16_t>(*next);
-			peripheral_bits_ = 9;
+			peripheral_bits_ = 8;
-			set_state(State::PostingByte);
+			set_state(State::AwaitingByteAcknowledge);
 		} else {
-			acknowledge();
 			set_state(State::AwaitingAddress);
 		}
 	};
@@ -123,7 +139,6 @@ void Bus::signal(Event event) {
 
 		case State::CollectingAddress:
 			capture_bit();
-
 			if(input_count_ == 8) {
 				auto pair = peripherals_.find(uint8_t(input_) & 0xfe);
 				if(pair != peripherals_.end()) {
@@ -132,8 +147,7 @@ void Bus::signal(Event event) {
 
 					if(input_&1) {
 						acknowledge();
-						set_state(State::PostingByte);
+						set_state(State::CompletingWriteAcknowledge);
-//						enqueue(active_peripheral_->read());
 					} else {
 						acknowledge();
 						set_state(State::ReceivingByte);
@@ -145,11 +159,9 @@ void Bus::signal(Event event) {
 		break;
 
 		case State::ReceivingByte:
-			// Run down the clock on the acknowledge bit.
+			if(event == Event::FinishedOutput) {
-			if(peripheral_bits_) {
 				return;
 			}
-
 			capture_bit();
 			if(input_count_ == 8) {
 				active_peripheral_->write(static_cast<uint8_t>(input_));
@@ -158,13 +170,24 @@ void Bus::signal(Event event) {
 			}
 		break;
 
-		case State::PostingByte:
+		case State::CompletingWriteAcknowledge:
-			// Finish whatever is enqueued.
+			if(event != Event::FinishedOutput) {
-			if(peripheral_bits_) {
+				break;
-				return;
+			}
+			enqueue(active_peripheral_->read());
+		break;
+
+		case State::AwaitingByteAcknowledge:
+			if(event == Event::FinishedOutput) {
+				break;
+			}
+			if(event != Event::Zero) {
+				logger.info().append("Peripheral byte not acknowledged");
+				state_ = State::AwaitingAddress;
+				break;
 			}
 
-			// Add a new byte (including its acknowledge bit).
+			// Add a new byte if there is one.
 			enqueue(active_peripheral_->read());
 		break;
 	}

Components/I2C/I2C.hpp

@@ -38,6 +38,7 @@ public:
 private:
 	bool data_ = false;
 	bool clock_ = false;
+	bool in_bit_ = false;
 	std::unordered_map<int, Peripheral *> peripherals_;
 
 	uint16_t input_ = 0xffff;
@@ -48,7 +49,7 @@ private:
 	int peripheral_bits_ = 0;
 
 	enum class Event {
-		Zero, One, Start, Stop,
+		Zero, One, Start, Stop, FinishedOutput,
 	};
 	void signal(Event);
 
@@ -56,7 +57,9 @@ private:
 		AwaitingAddress,
 		CollectingAddress,
 
-		PostingByte,
+		CompletingWriteAcknowledge,
+		AwaitingByteAcknowledge,
+
 		ReceivingByte,
 	} state_ = State::AwaitingAddress;
 };

Machines/Acorn/Archimedes/CMOSRAM.hpp

@@ -1,15 +1,16 @@
 //
-//  CMOSRAM.hpp
+// CMOSRAM.hpp
-//  Clock Signal
+// Clock Signal
 //
-//  Created by Thomas Harte on 20/03/2024.
+// Created by Thomas Harte on 20/03/2024.
-//  Copyright © 2024 Thomas Harte. All rights reserved.
+// Copyright © 2024 Thomas Harte. All rights reserved.
 //
 
 #pragma once
 
 #include "../../../Components/I2C/I2C.hpp"
 
+
 namespace Archimedes {
 
 struct CMOSRAM: public I2C::Peripheral {
@@ -18,16 +19,40 @@ struct CMOSRAM: public I2C::Peripheral {
 	}
 
 	std::optional<uint8_t> read() override {
-		return 0;
+		// VERY TEMPORARY. For now, borrowed from Arcem.
+		// To replace with whatever the system-written default is.
+		static constexpr uint8_t defaults[] = {
+			0x00, 0x83, 0x55, 0x16, 0x14, 0x09, 0x11, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x03, 0x14, 0x00, 0x6f, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x6d,
+			0x00, 0xfe, 0x00, 0xeb, 0x00, 0x08, 0x00, 0x00, 0x00, 0x00, 0x10, 0x50, 0x20, 0x08, 0x0a, 0x2c,
+			0x80, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x5c, 0x13, 0x00, 0x00, 0x04, 0xfd, 0x08, 0x01, 0xff, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0xf0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0a, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,
+		};
+		static_assert(sizeof(defaults) == 256);
+
+		const uint8_t result = defaults[address_];
+		++address_;
+		return result;
 	}
 
 	void write(uint8_t value) override {
 		if(expecting_address_) {
 			address_ = value;
+			expecting_address_ = false;
 		} else {
-			printf("Write to %d\n", address_);
 			++address_;
-			// TODO: write to RAM.
+			// TODO: write.
 		}
 	}