MSB2 Firmware

Overview

The MSB2 and LSB both use the same firmware core with custom modifications to support the sensors and other subsystems specific to each platform. The goals of the firmware are:

• Encapsulate all low level functions in easily accessible commands
  • Hides all startup/initialization routines
• Provide a variable sampling schedule (with some constraints) that automatically handles powering off unused sensors
• Provide commands for accessing calibration and other sensor metadata
• Sample and send data via a hi-speed binary uart interface
  • Communicates with any embedded platform
  • Communicates with any desktop/laptop/handheld/cell phone with a available uart port

State Diagram

The system has two main states, the default wait state and the running state. The other states are used for setting up various components of the system. Once everything is working; however, the user simply enters the running state and begins recording data. In addition to the command states shown here available here several other commands are available (depending upon the hardware) which can be used to manipulate various parts of the system.

System state diagram for communicating with the MSB firmware, the power point version is available here

Communication protocol

Communication with the MSB Firmware takes place over the first uart on the ATmega, at 921,600 baud, with an option of having flow control. You must only send one byte per timer interrupt! For example, if your INTERRUPT_COUNT is set to 5120 (512 Hz), you must wait at least 1/512th of a second between bytes.

Commands

Commands are six-character sequences where '!' (hex 0x21) indicates the start of a command. The parser is reset by a '!', so if you make a mistake when sending a command, simply resend the command starting with a '!'. Some commands include their arguments as part of their five command bytes.


Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5
'!'	0x21	Command

Note: '!' is a reserved character and may not be used as an argument for any command that includes its arguments in the command bytes.

LED Commands

LED commands are special one-byte commands that turns the LEDs on and off. Two LED command formats exist: one to adjust the individual LEDs, and one to adjust both the individual LEDs and the tri-color LED. In both formats, a 0 bit for an LED turns it on, and a 1 bit turns it off.


Individual LED command format

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
0	0	0	0	Red	Green	Blue	1

Individual and Tricolor LED command format

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
1	Tri-color Blue	Tri-color Green	Tri-color Red	Red	Green	Blue	1

Packet format (from the MSB Firmware)

All MSB firmware responses will be sent back as packets that begin with 2 characters '#' followed by '|', then an identifier byte describing what the packet is and how it should be interpreted.

Byte 0		Byte 1		Byte 2		...		Byte N
'#'	0x23	'|'	0x7C	ID		Payload		Checksum

The checksum is calculated by adding up all bytes 2 through N - 1, and taking the lower 8 bits of the result.

Packet IDs

ID	Type
0x00	Sensor Packet
0x01	Sensor Packet
0x02	RTC Packet
0x04	Error Packet
0x08	Microphone Packet
0x10	LEDs Packet
0x20	Calibration Packet
0x40	Schedule Packet
0x80	Power Packet

Example Communication Sequence

Here's an example of what a host computer would send to query the state of the LED and what it would receive from the MSB:

Host sends: '!query' + 0x10 [query command + 0x10 to indicate a LED query]

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5		Byte 6
'!'	0x21	'q'	0x71	'u'	0x75	'e'	0x65	'r'	0x72	'y'	0x79		0x10

MSB Firmware responds with: ['#|' start header + 0x10 to indicate a LED packet and 0x00 the current state of the LEDs

Byte 0		Byte 1		Byte 2		Byte 3
'#'	0x23	'|'	0x7C		0x10	0	0x00

Available Commands

Start Command

This command begins sampling of the sensors and outputting the readings. May only be executed in the WAIT state.

Host sends: '!start'

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5
'!'	0x21	's'	0x73	't'	0x74	'a'	0x61	'r'	0x72	't'	0x74

Cease Command

This command stops sampling of the sensors. May only be executed in the RUNNING state.

Host sends: '!cease'

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5
'!'	0x21	'c'	0x63	'e'	0x65	'a'	0x61	's'	0x73	'e'	0x65

Reset Command

This command reinitializes the sensor board. May only be executed in the WAIT state.

Host sends: '!reset'

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5
'!'	0x21	'r'	0x72	'e'	0x65	's'	0x73	'e'	0x65	't'	0x74

Alter Schedule Command

This command alters the sensor sampling schedule. May only be executed in the WAIT state.

Host sends: '!alter' SCHED_DATA

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5		Byte 6 - 23
'!'	0x21	'a'	0x61	'l'	0x6c	't'	0x74	'e'	0x65	'r'	0x72	Schedule Data

Data Returned

The MSB will verify that it can meet the desired schedule, and if not, will adjust it accordingly. In either case, the effective schedule will be returned over the serial port in the same format, except with "!alter" replaced with the MSB response bytes, with ID = 0x40.

Query Command

This command returns various information about the state of the MSB. May only be executed in the WAIT state.

Host sends: '!query' QUERY_ID

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5		Byte 6
'!'	0x21	'q'	0x71	'u'	0x75	'e'	0x65	'r'	0x72	'y'	0x79	Query ID

Query Types

ID	Type
0x40	Current Schedule
0x20	Calibration Information
0x10	LEDs State
0x02	RTC Registers

USB Enable Command

This command enables or disables the USB/Digital Compass power. May be executed in either the RUNNING or WAIT states.

Host sends: '!usb-0' or '!usb-1'

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5
'!'	0x21	'u'	0x75	's'	0x73	'b'	0x62	'-'	0x2d	USB status ('0' or '1')

GPS Enable Command

This command sets the state of the GPS Enable signal (Atmel_PA7). May be executed in either the RUNNING or WAIT states.

Host sends: '!gps-0' or '!gps-1'

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5
'!'	0x21	'g'	0x67	'p'	0x70	's'	0x73	'-'	0x2d	GPS enable ('0' or '1')

Gain Command

This command temporarily adjusts the gain while the sensors are being sampled. May only be executed in the RUNNING state.

Host sends: '!gain' GAIN_VALUE

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5
'!'	0x21	'g'	0x67	'a'	0x61	'i'	0x69	'n'	0x6e	Gain (0x00 to 0xFF)

Note: Since '!' is a reserved character, a gain value of 0x21 cannot be set with this command.

Write Command

This writes the current schedule to the EEPROM to be used as the default schedule. May only be executed in the WAIT state.

Host sends: '!write'

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5
'!'	0x21	'w'	0x77	'r'	0x72	'i'	0x69	't'	0x74	'e'	0x65

Clock Command

This writes sets the first seven bytes of the RTC registers. May only be executed in the WAIT state. More information on the RTC's registers is available in this datasheet.

Host sends: '!clock'

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5		Byte 6		Byte 7		Byte 8		Byte 9		Byte 10		Byte 11		Byte 12
'!'	0x21	'c'	0x63	'l'	0x6c	'o'	0x6f	'c'	0x63	'k'	0x6b	RTC Reg 0		RTC Reg 1		RTC Reg 2		RTC Reg 3		RTC Reg 4		RTC Reg 5		RTC Reg 6

RTCal Command

This writes sets the RTC's calibration register. May only be executed in the WAIT state. More information on the RTC's registers is available in this datasheet.

Host sends: '!rtcal'

Byte 0		Byte 1		Byte 2		Byte 3		Byte 4		Byte 5		Byte 6
'!'	0x21	'r'	0x72	't'	0x74	'c'	0x63	'a'	0x61	'l'	0x6c	RTC Reg 7

Data Format

Schedule Format

Byte 0	Byte 1	Byte 2	Byte 3	Byte 4	Byte 5	Byte 6	Byte 7	Byte 8	Byte 9
Interrupts Per 10 Secs		Mic Hz		Accelerometer Hz * 10		Ambient Light Hz * 10		Barometer Hz * 10
Low-order	High-order	Low-Order	High-Order	Low-Order	High-Order	Low-Order	High-Order	Low-Order	High-Order

Byte 10	Byte 11	Byte 12	Byte 13	Byte 14	Byte 15	Byte 16	Byte 17
Compass Hz * 10		DALS Hz * 10		Humidity Hz * 10		Power Control	Mic Gain
Low-order	High-order	Low-Order	High-Order	Low-Order	High-Order

Power Control Bits

Certain sensors can be powered down in between samples. To enable this, set the appropriate bits in the power control byte. Note that due to the amount of time required to power up and down the sensors, the maximum sampling rate will be decreased for these sensors.

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
0	0	0	0	0	Accel	Compass	DALS

Microphone Gain

This byte ranges from 0 to 255. 0 represents minimal gain, while 255 represents maximal gain. The gain may also be adjusted during sampling with the !gain command.