batt_smbus: Adds ManufacturerAccess, write_reg, and write_block functions

Also fixes the the PEC calculation for writing. See
http://cache.freescale.com/files/32bit/doc/app_note/AN4471.pdf and
http://www.ti.com/lit/an/sloa132/sloa132.pdf for more details for more
details on SMBus reading and writing including with and without PECs.

src/drivers/batt_smbus/batt_smbus.cpp

@@ -92,9 +92,13 @@
 #define BATT_SMBUS_MANUFACTURE_NAME	0x20	///< manufacturer name
 #define BATT_SMBUS_MANUFACTURE_INFO	0x25	///< cell voltage register
 #define BATT_SMBUS_CURRENT              0x2a	///< current register
-#define BATT_SMBUS_MEASUREMENT_INTERVAL_MS	(1000000 / 10)	///< time in microseconds, measure at 10hz
+#define BATT_SMBUS_MEASUREMENT_INTERVAL_MS	(1000000 / 10)	///< time in microseconds, measure at 10Hz
 #define BATT_SMBUS_TIMEOUT_MS           10000000	///< timeout looking for battery 10seconds after startup
 
+#define BATT_SMBUS_MANUFACTURER_ACCESS	0x00
+#define BATT_SMBUS_MANUFACTURER_DATA	0x23
+#define BATT_SMBUS_MANUFACTURER_BLOCK_ACCESS    0x44
+
 #define BATT_SMBUS_PEC_POLYNOMIAL	0x07	///< Polynomial for calculating PEC
 
 #ifndef CONFIG_SCHED_WORKQUEUE
@@ -166,18 +170,35 @@ private:
 	 */
 	int			read_reg(uint8_t reg, uint16_t &val);
 
+	/**
+	 * Write a word to specified register
+	 */
+	int			write_reg(uint8_t reg, uint16_t val);
+
 	/**
 	 * Read block from bus
 	 * @return returns number of characters read if successful, zero if unsuccessful
 	 */
 	uint8_t			read_block(uint8_t reg, uint8_t *data, uint8_t max_len, bool append_zero);
 
+	/**
+	 * Write block to the bus
+	 * @return the number of characters sent if successful, zero if unsuccessful
+	 */
+	uint8_t			write_block(uint8_t reg, uint8_t *data, uint8_t len);
+
 	/**
 	 * Calculate PEC for a read or write from the battery
 	 * @param buff is the data that was read or will be written
 	 */
 	uint8_t			get_PEC(uint8_t cmd, bool reading, const uint8_t buff[], uint8_t len) const;
 
+	/**
+	 * Write a word to Manufacturer Access register (0x00)
+	 * @param cmd the word to be written to Manufacturer Access
+	 */
+	uint8_t			ManufacturerAccess(uint16_t cmd);
+
 	// internal variables
 	bool			_enabled;	///< true if we have successfully connected to battery
 	work_s			_work;		///< work queue for scheduling reads
@@ -480,6 +501,27 @@ BATT_SMBUS::read_reg(uint8_t reg, uint16_t &val)
 	return ret;
 }
 
+int
+BATT_SMBUS::write_reg(uint8_t reg, uint16_t val)
+{
+	uint8_t buff[4];  // reg + 2 bytes of data + PEC
+
+	buff[0] = reg;
+	buff[2] = uint8_t(val << 8) & 0xff;
+	buff[1] = (uint8_t)val;
+	buff[3] = get_PEC(reg, false, &buff[1],  2); // Append PEC
+
+	// write bytes to register
+	int ret = transfer(buff, 3, nullptr, 0);
+
+	if (ret != OK) {
+		debug("Register write error");
+	}
+
+	// return success or failure
+	return ret;
+}
+
 uint8_t
 BATT_SMBUS::read_block(uint8_t reg, uint8_t *data, uint8_t max_len, bool append_zero)
 {
@@ -520,6 +562,31 @@ BATT_SMBUS::read_block(uint8_t reg, uint8_t *data, uint8_t max_len, bool append_
 	return bufflen;
 }
 
+uint8_t
+BATT_SMBUS::write_block(uint8_t reg, uint8_t *data, uint8_t len)
+{
+	uint8_t buff[len + 3];  // buffer to hold results
+
+	usleep(1);
+
+	buff[0] = reg;
+	buff[1] = len;
+	memcpy(&buff[2], data, len);
+	buff[len + 2] = get_PEC(reg, false, &buff[1],  len + 1); // Append PEC
+
+	// send bytes
+	int ret = transfer(buff, len + 3, nullptr, 0);
+
+	// return zero on failure
+	if (ret != OK) {
+		debug("Block write error\n");
+		return 0;
+	}
+
+	// return success
+	return len;
+}
+
 uint8_t
 BATT_SMBUS::get_PEC(uint8_t cmd, bool reading, const uint8_t buff[], uint8_t len) const
 {
@@ -528,13 +595,33 @@ BATT_SMBUS::get_PEC(uint8_t cmd, bool reading, const uint8_t buff[], uint8_t len
 		return 0;
 	}
 
-	// prepare temp buffer for calcing crc
-	uint8_t tmp_buff[len + 3];
+	/**
+	 *  Note: The PEC is calculated on all the message bytes. See http://cache.freescale.com/files/32bit/doc/app_note/AN4471.pdf
+	 *  and http://www.ti.com/lit/an/sloa132/sloa132.pdf for more details
+	 */
+
+	// prepare temp buffer for calculating crc
+	uint8_t tmp_buff_len;
+
+	if (reading) {
+		tmp_buff_len = len + 3;
+
+	} else {
+		tmp_buff_len = len + 2;
+	}
+
+	uint8_t tmp_buff[tmp_buff_len];
 	tmp_buff[0] = (uint8_t)get_address() << 1;
 	tmp_buff[1] = cmd;
+
+	if (reading) {
 		tmp_buff[2] = tmp_buff[0] | (uint8_t)reading;
 		memcpy(&tmp_buff[3], buff, len);
 
+	} else {
+		memcpy(&tmp_buff[2], buff, len);
+	}
+
 	// initialise crc to zero
 	uint8_t crc = 0;
 	uint8_t shift_reg = 0;
@@ -561,6 +648,19 @@ BATT_SMBUS::get_PEC(uint8_t cmd, bool reading, const uint8_t buff[], uint8_t len
 	return crc;
 }
 
+uint8_t
+BATT_SMBUS::ManufacturerAccess(uint16_t cmd)
+{
+	// write bytes to Manufacturer Access
+	int ret = write_reg(BATT_SMBUS_MANUFACTURER_ACCESS, cmd);
+
+	if (ret != OK) {
+		debug("Manufacturer Access error");
+	}
+
+	return ret;
+}
+
 ///////////////////////// shell functions ///////////////////////
 
 void