HAB-GPS2-bridge - 源码 - 源码 - 免费下载

HAB-GPS2-bridge

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源码售价： 5 个金币积分规则积分充值

资源说明：This is the firmware for the bridge between eTrex Legend serial and I2C bus

This application is a component of HAB, the high-altitude balloon flight controller.  It provides a bridge between to incoming serial data from the backup GPS (an eTrex Legend) and the main flight computer's I2C bus.  Rather than use a larger MCU to provide more on-board USARTs, we chose a bridge.  Further the secondary control off-loads the GPS stream parsing from the primary controller.

### Garmin Text Output Mode Description ###



FIELD DESCRIPTION: WIDTH: NOTES:

  Sentence start 1 Always '@'

T
I
M
E

Year 2 Last two digits of UTC year

Month 2 UTC month, "01".."12"

Day 2 UTC day of month, "01".."31"

Hour 2 UTC hour, "00".."23"

Minute 2 UTC minute, "00".."59"

Second 2 UTC second, "00".."59"


P
O
S
I
T
I
O
N

Latitude hemisphere 1 'N' or 'S'

Latitude position 7 WGS84 ddmmmmm, with an implied
                                        decimal after the 4th digit

Longitude hemishpere 1 'E' or 'W'

Longitude position 8 WGS84 dddmmmmm with an implied
                                         decimal after the 5th digit

Position status 1 'd' if current 2D differential GPS 
                                    position

                                    'D' if current 3D differential GPS 
                                    position

                                    'g' if current 2D GPS position

                                    'G' if current 3D GPS position

                                    'S' if simulated position

                                    '_' if invalid position

Horizontal posn error 3 EPH in meters

Altitude sign 1 '+' or '-'

Altitude 5 Height above or below mean
                                sea level in meters

V
E
L
O
C
I
T
Y

East/West velocity
direction 1 'E' or 'W'

East/West velocity
magnitude 4 
Meters per second in tenths, ("1234" = 123.4 m/s)

North/South velocity
direction 1 'N' or 'S'

North/South velocity
magnitude 4 Meters
per second in tenths, ("1234" = 123.4 m/s)

Vertical velocity
direction 1 'U' (up) or 'D' (down)

Vertical velocity
magnitude 4 Meters
per second in hundredths, ("1234" = 12.34 m/s)

 
Sentence end 2 Carriage return, '0x0D', and
                                    line feed, '0x0A'


## Target MCU ##
This code has been tested on an ATmega 328 AVR; but the code is compact enough to work with controllers with less flash memory - such as an ATmega 48 or ATmega 88.  The optimized code is just under 4K; so an ATmega 48 may work acceptably.

To [reduce the USART error](http://electronics.stackexchange.com/questions/5850/how-critical-are-uart-frequencies), the clock frequency should be:

* 1.8432 MHz
* 3.6864 MHz
* 7.3728 MHz
* 14.7456 MHz
* 16.5888 MHz

---

## Project files ##

### settings.h/.c ###
The settings files provide persistent settings functionality for the application.  Additional settings can be added by modifying the `settings_record_t` `struct`.  


### gps.h/.c ###
The gps file mainly takes care of parsing the Garmin text strings from the GPS.  Currently, it provides a limited amount of data.

To access coordinates components (lat/long) use the `gps_data` structure like:

    gps_data.coordinate.latitude.degrees


### TWI_slave.h/.c ###
The interface to the TWI/I2C bus.  This code is provided by Atmel.

---

## Operation ##

This device responds to the following operation codes:

#### E_W_DIR  0x20 ####
Returns the diretion of the East-West velocity vector as single byte character (E/W)

#### E_W_VEL 0x21 ####
Returns the magnitude of the East-West velocity vector as 2 bytes representing m/s * 100

#### N_S_DIR 0x22 ####
Returns the direction of North-South velocity vector as single character (N/S)

#### N_S_VEL 0x23 ####
Returns the magnitude of the North-South velocity vector as 2 bytes representing m/s * 100

#### VERT_DIR 0x24 ####
Returns the direction of the vertical velocity vector as single character (U/D)

#### VERT_VEL 0x25 ####
REturns the magnitude of the vertical velocity vector as 2 bytes representing m/s * 10

#### LAT 0x40 ####
Returns four bytes of data in the following order: direction (N/S), degrees, minutes, seconds.

#### LON 0x41 ####
Returns four bytes of data in the following order: direction (E/W), degrees, minutes, seconds.

#### FIX_TIME 0x50 ####
Returns the time for the current fix as as `fix_time_t` object expressed in six bytes for `year`, `month`, `day`, `hour`, `minute`, `second`.

#### DEBUG_ON 0x60 ####
Turns debugging on.  This enables display of visual data at PB2.  Returns `I2C_DEBUG_CONFIRM_BYTE`

#### DEBUG_OFF 0x61 ####
Turns off debugging.  Returns `I2C_DEBUG_CONFIRM_BYTE`.

#### TEST 0x02	####
Flashes diagnostic LED for testing purposes.

FIELD DESCRIPTION:	WIDTH:	NOTES:
	Sentence start	1	Always '@'
T I M E	Year	2	Last two digits of UTC year
Month	2	UTC month, "01".."12"
Day	2	UTC day of month, "01".."31"
Hour	2	UTC hour, "00".."23"
Minute	2	UTC minute, "00".."59"
Second	2	UTC second, "00".."59"
P O S I T I O N	Latitude hemisphere	1	'N' or 'S'
Latitude position	7	WGS84 ddmmmmm, with an implied decimal after the 4th digit
Longitude hemishpere	1	'E' or 'W'
Longitude position	8	WGS84 dddmmmmm with an implied decimal after the 5th digit
Position status	1	'd' if current 2D differential GPS position 'D' if current 3D differential GPS position 'g' if current 2D GPS position 'G' if current 3D GPS position 'S' if simulated position '_' if invalid position
Horizontal posn error	3	EPH in meters
Altitude sign	1	'+' or '-'
Altitude	5	Height above or below mean sea level in meters
V E L O C I T Y	East/West velocity direction	1	'E' or 'W'
East/West velocity magnitude	4	Meters per second in tenths, ("1234" = 123.4 m/s)
North/South velocity direction	1	'N' or 'S'
North/South velocity magnitude	4	Meters per second in tenths, ("1234" = 123.4 m/s)
Vertical velocity direction	1	'U' (up) or 'D' (down)
Vertical velocity magnitude	4	Meters per second in hundredths, ("1234" = 12.34 m/s)
	Sentence end	2	Carriage return, '0x0D', and line feed, '0x0A'

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