constexpr-ify log field list (#2548)

* constexprify

* reclaim ram

* more constexpr

Co-authored-by: Matthew Kennedy <makenne@microsoft.com>

firmware/console/binary_log/binary_logging.cpp

@@ -18,7 +18,7 @@ static scaled_channel<uint32_t, TIME_PRECISION> packedTime;
 
 // todo: we are at the edge of sdLogBuffer size and at the moment we have no code to make sure buffer does not overflow
 // todo: make this logic smarter
-static const LogField fields[] = {
+static constexpr LogField fields[] = {
 	{tsOutputChannels.rpm, GAUGE_NAME_RPM, "rpm", 0},
 	{packedTime, GAUGE_NAME_TIME, "sec", 0},
 	{tsOutputChannels.totalTriggerErrorCounter, GAUGE_NAME_TRG_ERR, "err", 0},
@@ -74,6 +74,17 @@ static const LogField fields[] = {
 	{tsOutputChannels.knockLevel, GAUGE_NAME_KNOCK_LEVEL, "dBv", 0},
 };
 
+static constexpr uint16_t computeFieldsRecordLength() {
+	uint16_t recLength = 0;
+	for (size_t i = 0; i < efi::size(fields); i++) {
+		recLength += fields[i].getSize();
+	}
+
+	return recLength;
+}
+
+static constexpr uint16_t recordLength = computeFieldsRecordLength();
+
 void writeHeader(Writer& outBuffer) {
 	char buffer[MLQ_HEADER_SIZE];
 	// File format: MLVLG\0
@@ -102,13 +113,8 @@ void writeHeader(Writer& outBuffer) {
 	buffer[17] = headerSize & 0xFF;
 
 	// Record length - length of a single data record: sum size of all fields
-	uint16_t recLength = 0;
-	for (size_t i = 0; i < efi::size(fields); i++) {
-		recLength += fields[i].getSize();
-	}
-
-	buffer[18] = recLength >> 8;
-	buffer[19] = recLength & 0xFF;
+	buffer[18] = recordLength >> 8;
+	buffer[19] = recordLength & 0xFF;
 
 	// Number of logger fields
 	buffer[20] = 0;

firmware/console/binary_log/log_field.h

@@ -8,10 +8,10 @@ struct Writer;
 class LogField {
 public:
 	template <typename TValue, int TMult = 1>
-	LogField(const scaled_channel<TValue, TMult>& toRead, const char* name, const char* units, int8_t digits)
+	constexpr LogField(const scaled_channel<TValue, TMult>& toRead, const char* name, const char* units, int8_t digits)
 		: m_type(resolveType<TValue>())
 		, m_multiplier(TMult)
-		, m_addr(reinterpret_cast<const char*>(&toRead))
+		, m_addr(toRead.getFirstByteAddr())
 		, m_digits(digits)
 		, m_size(sizeForType(resolveType<TValue>()))
 		, m_name(name)
@@ -30,7 +30,7 @@ public:
 		F32 = 7,
 	};
 
-	size_t getSize() const {
+	constexpr size_t getSize() const {
 		return m_size;
 	}
 
@@ -43,9 +43,9 @@ public:
 
 private:
 	template<typename T>
-	static Type resolveType();
+	static constexpr Type resolveType();
 
-	static size_t sizeForType(Type t) {
+	static constexpr size_t sizeForType(Type t) {
 		switch (t) {
 			case Type::U08:
 			case Type::S08:

firmware/controllers/engine_controller.cpp

@@ -709,7 +709,7 @@ void initEngineContoller(Logging *sharedLogger DECLARE_ENGINE_PARAMETER_SUFFIX)
  * UNUSED_SIZE constants.
  */
 #ifndef RAM_UNUSED_SIZE
-#define RAM_UNUSED_SIZE 2850
+#define RAM_UNUSED_SIZE 4350
 #endif
 #ifndef CCM_UNUSED_SIZE
 #define CCM_UNUSED_SIZE 2000

firmware/util/scaled_channel.h

@@ -23,19 +23,26 @@
 template <typename T, int mult = 1>
 class scaled_channel {
 public:
-	scaled_channel() : m_value(static_cast<T>(0)) { }
-	scaled_channel(float val)
+	constexpr scaled_channel() : m_value(static_cast<T>(0)) { }
+	constexpr scaled_channel(float val)
 		: m_value(val * mult)
 	{
 	}
 
 	// Allow reading back out as a float (note: this may be lossy!)
-	operator float() const {
+	constexpr operator float() const {
 		return m_value / (float)mult;
 	}
 
+	constexpr const char* getFirstByteAddr() const {
+		return &m_firstByte;
+	}
+
 private:
-	T m_value;
+	union {
+		T m_value;
+		char m_firstByte;
+	};
 };
 
 // We need to guarantee that scaled values containing some type are the same size