AmdFlash: Support continuity check command.

This function allows the program to check for correct connectivity of the flash
chip, and would fail if there are shorts on adjacent address and data pins.

It seems to be specific to the Infineon / Cypress / Spansion S29GL064S, at least
I haven’t seen it being offered elsewhere.

src/memory/AmdFlash.cc

@@ -241,7 +241,7 @@ uint8_t AmdFlash::peek(size_t address) const
 		} else {
 			return narrow_cast<uint8_t>(peekCFI(address));
 		}
-	} else if (state == State::PRGERR) {
+	} else if (state == one_of(State::STATUS, State::PRGERR)) {
 		return status;
 	} else {
 		UNREACHABLE;
@@ -454,9 +454,10 @@ bool AmdFlash::isSectorWritable(size_t sector) const
 
 uint8_t AmdFlash::read(size_t address)
 {
-	// note: after a read we stay in the same mode
 	const uint8_t value = peek(address);
-	if (state == State::PRGERR) {
+	if (state == State::STATUS) {
+		setState(State::IDLE);
+	} else if (state == State::PRGERR) {
 		status ^= 0x40;
 	}
 	return value;
@@ -486,6 +487,9 @@ void AmdFlash::write(size_t address, uint8_t value)
 		    checkCommandBufferProgram() ||
 		    checkCommandEraseChip() ||
 		    checkCommandCFIQuery() ||
+		    checkCommandContinuityCheck() ||
+		    checkCommandStatusRead() ||
+		    checkCommandStatusClear() ||
 		    checkCommandLongReset() ||
 		    checkCommandReset()) {
 			// do nothing, we're still matching a command, but it is not complete yet
@@ -508,6 +512,14 @@ void AmdFlash::write(size_t address, uint8_t value)
 		} else {
 			cmd.clear();
 		}
+	} else if (state == State::STATUS) {
+		// TODO confirm. S29GL064S datasheet: "it is not recommended".
+		if (checkCommandLongReset() ||
+		    checkCommandReset()) {
+			// do nothing, we're still matching a command, but it is not complete yet
+		} else {
+			cmd.clear();
+		}
 	} else if (state == State::PRGERR) {
 		if (checkCommandLongReset() ||
 		    (chip.program.shortAbortReset && checkCommandReset())) {
@@ -543,6 +555,35 @@ bool AmdFlash::checkCommandLongReset()
 	return false;
 }
 
+bool AmdFlash::checkCommandStatusRead()
+{
+	static constexpr std::array<uint8_t, 1> cmdSeq = {0x70};
+	if (chip.misc.statusCommand && partialMatch(cmdSeq)) {
+		setState(State::STATUS);
+	}
+	return false;
+}
+
+bool AmdFlash::checkCommandStatusClear()
+{
+	static constexpr std::array<uint8_t, 1> cmdSeq = {0x71};
+	if (chip.misc.statusCommand && partialMatch(cmdSeq)) {
+		softReset();
+	}
+	return false;
+}
+
+bool AmdFlash::checkCommandContinuityCheck()
+{
+	if (chip.misc.continuityCommand && cmd[0] == AddressValue{0x5554AB, 0xFF}) {
+		if (cmd.size() < 2) return true;
+		if (cmd.size() == 2 && cmd[1] == AddressValue{0x2AAB54, 0x00}) {
+			status |= 0x01;
+		}
+	}
+	return false;
+}
+
 bool AmdFlash::checkCommandCFIQuery()
 {
 	// convert byte address to native address
@@ -700,6 +741,7 @@ static constexpr std::initializer_list<enum_string<AmdFlash::State>> stateInfo =
 	{ "IDLE",   AmdFlash::State::IDLE  },
 	{ "IDENT",  AmdFlash::State::IDENT },
 	{ "CFI",    AmdFlash::State::CFI },
+	{ "STATUS", AmdFlash::State::STATUS },
 	{ "PRGERR", AmdFlash::State::PRGERR }
 };
 SERIALIZE_ENUM(AmdFlash::State, stateInfo);

src/memory/AmdFlash.hh

@@ -136,17 +136,28 @@ public:
 		}
 	};
 
+	struct Misc {
+		bool statusCommand : 1 = false;
+		bool continuityCommand : 1 = false;
+
+		constexpr void validate() const {
+			assert(!continuityCommand || statusCommand);
+		}
+	};
+
 	struct Chip {
 		AutoSelect autoSelect;
 		Geometry geometry;
 		Program program = {};
 		CFI cfi = {};
+		Misc misc = {};
 
 		constexpr void validate() const {
 			autoSelect.validate();
 			geometry.validate();
 			program.validate();
 			cfi.validate();
+			misc.validate();
 		}
 	};
 
@@ -208,11 +219,13 @@ public:
 		size_t addr;
 		uint8_t value;
 
+		auto operator<=>(const AddressValue&) const = default;
+
 		template<typename Archive>
 		void serialize(Archive& ar, unsigned version);
 	};
 
-	enum class State { IDLE, IDENT, CFI, PRGERR };
+	enum class State { IDLE, IDENT, CFI, STATUS, PRGERR };
 
 private:
 	void init(const std::string& name, const DeviceConfig& config, Load load,
@@ -229,6 +242,8 @@ private:
 	[[nodiscard]] bool checkCommandLongReset();
 	[[nodiscard]] bool checkCommandCFIQuery();
 	[[nodiscard]] bool checkCommandCFIExit();
+	[[nodiscard]] bool checkCommandStatusRead();
+	[[nodiscard]] bool checkCommandStatusClear();
 	[[nodiscard]] bool checkCommandEraseSector();
 	[[nodiscard]] bool checkCommandEraseChip();
 	[[nodiscard]] bool checkCommandProgramHelper(size_t numBytes, std::span<const uint8_t> cmdSeq);
@@ -237,6 +252,7 @@ private:
 	[[nodiscard]] bool checkCommandQuadrupleByteProgram();
 	[[nodiscard]] bool checkCommandBufferProgram();
 	[[nodiscard]] bool checkCommandAutoSelect();
+	[[nodiscard]] bool checkCommandContinuityCheck();
 	[[nodiscard]] bool partialMatch(std::span<const uint8_t> dataSeq) const;
 
 	[[nodiscard]] bool isSectorWritable(size_t sector) const;