Chief Delphi - Example gyro code released.

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Example gyro code released.

I've written example gyro interface code and posted it here: http://kevin.org/frc. This code has been substantially revised since the version released earlier with the PID and scripting code. A substantial amount of documentation has also been written to support this code. As the programming interface has changed, this code will not work with the current version of robot.c. An updated version of robot.c will be released soon.

Here's the readme.txt:

Code:

The source code in gyro.c/.h contains a driver and supporting 

software to interface a variety of inexpensive gyros to your

robot controller. This software was tested with Analog Devices'

ADXRS150EB and ADXRS300EB gyros. Data sheets for these devices 

are included. Support for the ADXRS401EB is also included. By

default, this software is configured to work with a ADXRS150EB

gyro, sampling at 400Hz, downconverting to an update rate of

50Hz by averaging eight samples per update. These parameters

can be changed by editing gyro.h.

This software makes the assumption that when it's running, it 

solely controls the analog to digital conversion hardware and 

that only the gyro, on analog input one, is being sampled.

Calling Disable_Gyro() will disable the gyro software and

allow you to use the ADC for other purposes.

This source code will work with the Robovation (A/K/A EDU-RC) 

robot controller and the FIRST Robotics robot controller.

Wiring-up the ADXRS401EB, ADXRS150EB and ADXRS300EB gyro

evaluation boards is straightforward. Grab a PWM cable and cut

off the male end and strip the three wires back a centimeter 

or so. With a low wattage soldering iron, solder the white wire 

to the RATEOUT pin, solder the black wire to the AGND pin, the 

red wire to the AVCC pin, and finally connect a jumper wire 

between the AVCC and PDD pins. Plug the female end into the 

robot controller's analog input 1.

For optimum performance, you'll need to calibrate the scaling

factor to match that of your gyro's. One way to calibrate your 

gyro is to mount it very securely to a hefty, square or 

rectangular object. Mounting the gyro to a hefty object will 

help dampen higher frequency vibrations that can adversly 

effect your measurements. Place the mounted gyro against 

another square object and start the included demonstration 

software. To get good results, the mount must be absolutely 

still when the "Calibrating Gyro Bias..." message appears on 

the terminal screen. After a few seconds, the gyro angular rate 

and angle will be sent to the terminal screen. If the angle 

drifts rapidly while the mounted gyro is motonless, you need 

to restart the software to acquire a new gyro bias measurement. 

Again, gyros are very sensitive and must be still while the bias 

is calculated. Once the gyro is running with little drift, 

rotate the mount 180 degrees and note the reported angle. If the 

angular units are set to tenths of a degree, the ideal reported 

angle is 1800. If set to milliradians, the ideal angle 1s 3142 

(Pi times a thousand). For every tenth of a percent that the 

angle is high, decrease the GYRO_CAL_FACTOR numerator by one.

Conversly, for every tenth of a percent low, increase the 

numerator by one. Repeat until you're satisfied with the 

accuracy.

If you find that the Calc_Gyro_Bias() function doesn't do

a good enough job of calculating a bias for your particular

gyro, another option is to average the gyro bias for a much

longer period of time and manually set the gyro bias using

the function Set_Gyro_Bias(). An example that shows how to

do this is commented out in the accompaning user_routines.c/

Process_Data_From_Master_uP(). With a perfectly still gyro,

running this example code will display a running average gyro 

bias that should converge to one value over time. Enter this 

value into the call to Set_Gyro_bias() and comment out or 

remove the call to Calc_Gyro_Bias(). Now perform the gyro 

scaling factor calibration described above. 

The included project files were built with MPLAB version 6.60.

If your version of MPLAB complains about the project version, 

the best thing to do is just create a new project with MPLAB's 

project wizard. Include every file except: FRC_alltimers.lib 

and ifi_alltimers.lib and you should be able to build the code.

****************************************************************

Here's a description of the functions in gyro.c:



Initialize_Gyro()

This function initializes the gyro software. It should be called 

from user_routines.c/User_Initialization().

 

Get_Gyro_Rate()

This function returns the current angular rate of change in 

units of milliradians per second. If desired, the angular unit 

can be changed to tenths of a degree per second by modifying

the angular units #define entry in gyro.h



Get_Gyro_Angle()

This function returns the change in heading angle, in 

milliradians, since the software was initialized or 

Reset_Gyro_Angle() was called. If desired, the angular unit

can be changed to tenths of a degree by modifying the angular

units #define entry in gyro.h



Calc_Gyro_Bias()

This function forces a new gyro bias calculation to take place.

For best results, this should be called about a half second 

after the robot powers-up and while the robot is perfectly still 

with all vibration sources turned off (e.g., compressor). It's a

good idea to call this function whenever you know the robot will

be completely still for about twenty-five milliseconds. For

example, call this function just after you've completed a

straight line drive, and just before doing a turn-in-place.



Get_Gyro_Bias()

This function returns the current calculated gyro bias. For

extra precision, this software internally maintains a gyro bias

value that is the sum of GYRO_SAMPLES_PER_UPDATE samples of the 

gyro's analog output. By default, GYRO_SAMPLES_PER_UPDATE is

set to a value of eight in gyro.h



Set_Gyro_Bias()

This function can be called to manually set the gyro bias. For

extra precision, this software internally maintains a gyro bias

value that is the sum of GYRO_SAMPLES_PER_UPDATE samples of the 

gyro's analog output. By default, GYRO_SAMPLES_PER_UPDATE is

set to a value of eight in gyro.h



Reset_Gyro_Angle()

This function resets the integrated gyro heading angle to zero.



Disable_Gyro()

This function should be called when the gyro functionality is

no longer needed, thus reclaiming the time spent servicing the

timer 2 interrupt.



Initialize_ADC()

This function initializes the analog to digital conversion

hardware. This is called by Initialize_Gyro() above and 

shouldn't be called directly.



Initialize_Timer_2()

This function initializes and starts timer2. This is called by

Initialize_Gyro() above and shouldn't be called directly.



Timer_2_Int_Handler()

This function is automatically called when timer 2 causes an

interrupt and shouldn't be called directly.



****************************************************************

Six things must be done before this software will work 

correctly on the FRC-RC:

1) The gyro's rate output is wired to analog input 1.

2) A #include statement for the gyro.h header file must be 

included at the beginning of each source file that calls the 

functions in this source file. The statement should look like 

this: #include "gyro.h".

3) Initialize_Gyro() must be called from user_routines.c/

User_Initialization().

4) The timer 2 interrupt handler, Timer_2_Int_Handler(), must

be installed in User_Routines_Fast.c/InterruptHandlerLow().

See the accompanying copy of User_Routines_Fast.c to see how

this is done.

5) You must select the gyro you're using from a list in gyro.h

and if needed, remove the // in front of it's #define.

6) For optimal performance, you'll need to calibrate the gyro 

scaling factor using the instructions above or those included

in gyro.h.        



Eight things must be done before this software will work 

correctly on the EDU-RC:

1) The gyro's rate output is wired to analog input 1.

2) IO1 must be configured as an "INPUT" in user_routines.c/

User_Initialization().

3) The call to Set_Number_of_Analog_Channels() must configure

at least one analog channel.

4) A #include statement for the gyro.h header file must be 

included at the beginning of each source file that calls the 

functions in this source file. The statement should look like 

this: #include "gyro.h".

5) Initialize_Gyro() must be called from user_routines.c/

User_Initialization().

6) The timer 2 interrupt handler, Timer_2_Int_Handler(), must

be installed in User_Routines_Fast.c/InterruptHandlerLow().

See the accompanying copy of User_Routines_Fast.c to see how

this is done.

7) You must select the gyro you're using from a list in gyro.h

and if needed, remove the // in front of it's #define.

8) For optimal performance, you'll need to calibrate the gyro 

scaling factor using the instructions above or those included

in gyro.h.

-Kevin