PWM Class Reference

#include <PWM.h>

Inheritance diagram for PWM:

List of all members.

Public Types
enum	PeriodMultiplier { kPeriodMultiplier_1X = 1, kPeriodMultiplier_2X = 2, kPeriodMultiplier_4X = 4 }
Public Member Functions
	PWM (UINT32 channel)
	PWM (UINT8 moduleNumber, UINT32 channel)
virtual	~PWM ()
virtual void	SetRaw (UINT8 value)
virtual UINT8	GetRaw ()
void	SetPeriodMultiplier (PeriodMultiplier mult)
void	EnableDeadbandElimination (bool eliminateDeadband)
void	SetBounds (INT32 max, INT32 deadbandMax, INT32 center, INT32 deadbandMin, INT32 min)
UINT32	GetChannel ()
UINT32	GetModuleNumber ()
Protected Member Functions
virtual void	SetPosition (float pos)
virtual float	GetPosition ()
virtual void	SetSpeed (float speed)
virtual float	GetSpeed ()
Protected Attributes
bool	m_eliminateDeadband
INT32	m_maxPwm
INT32	m_deadbandMaxPwm
INT32	m_centerPwm
INT32	m_deadbandMinPwm
INT32	m_minPwm
Static Protected Attributes
static const UINT32	kDefaultPwmPeriod = 774
static const UINT32	kDefaultMinPwmHigh = 102
static const INT32	kPwmDisabled = 0
Friends
class	DigitalModule

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Detailed Description

Class implements the PWM generation in the FPGA.

The values supplied as arguments for PWM outputs range from -1.0 to 1.0. They are mapped to the hardware dependent values, in this case 0-255 for the FPGA. Changes are immediately sent to the FPGA, and the update occurs at the next FPGA cycle. There is no delay.

As of revision 0.1.10 of the FPGA, the FPGA interprets the 0-255 values as follows:

• 255 = full "forward"
• 254 to 129 = linear scaling from "full forward" to "center"
• 128 = center value
• 127 to 2 = linear scaling from "center" to "full reverse"
• 1 = full "reverse"
• 0 = disabled (i.e. PWM output is held low)

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Constructor & Destructor Documentation

PWM::PWM

(

UINT32

channel

)

[explicit]

Allocate a PWM in the default module given a channel.

Using a default module allocate a PWM given the channel number. The default module is the first slot numerically in the cRIO chassis.

Parameters:

channel

The PWM channel on the digital module.

PWM::PWM	(	UINT8	moduleNumber,
		UINT32	channel
	)

Allocate a PWM given a module and channel. Allocate a PWM using a module and channel number.

Parameters:

moduleNumber	The digital module (1 or 2).
channel	The PWM channel on the digital module (1..10).

PWM::~PWM

(

)

[virtual]

Free the PWM channel.

Free the resource associated with the PWM channel and set the value to 0.

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Member Function Documentation

void PWM::EnableDeadbandElimination

(

bool

eliminateDeadband

)

Optionally eliminate the deadband from a speed controller.

Parameters:

eliminateDeadband

If true, set the motor curve on the Jaguar to eliminate the deadband in the middle of the range. Otherwise, keep the full range without modifying any values.

float PWM::GetPosition

(

)

[protected, virtual]

Get the PWM value in terms of a position.

This is intended to be used by servos.

Precondition:

SetMaxPositivePwm() called.

SetMinNegativePwm() called.

Returns:

The position the servo is set to between 0.0 and 1.0.

UINT8 PWM::GetRaw

(

)

[virtual]

Get the PWM value directly from the hardware.

Read a raw value from a PWM channel.

Returns:

Raw PWM control value. Range: 0 - 255.

float PWM::GetSpeed

(

)

[protected, virtual]

Get the PWM value in terms of speed.

This is intended to be used by speed controllers.

Precondition:

SetMaxPositivePwm() called.

SetMinPositivePwm() called.

SetMaxNegativePwm() called.

SetMinNegativePwm() called.

Returns:

The most recently set speed between -1.0 and 1.0.

void PWM::SetBounds	(	INT32	max,
		INT32	deadbandMax,
		INT32	center,
		INT32	deadbandMin,
		INT32	min
	)

Set the bounds on the PWM values. This sets the bounds on the PWM values for a particular each type of controller. The values determine the upper and lower speeds as well as the deadband bracket.

Parameters:

max	The Minimum pwm value
deadbandMax	The high end of the deadband range
center	The center speed (off)
deadbandMin	The low end of the deadband range
min	The minimum pwm value

void PWM::SetPeriodMultiplier

(

PeriodMultiplier

mult

)

Slow down the PWM signal for old devices.

Parameters:

mult	The period multiplier to apply to this channel

void PWM::SetPosition

(

float

pos

)

[protected, virtual]

Set the PWM value based on a position.

This is intended to be used by servos.

Precondition:

SetMaxPositivePwm() called.

SetMinNegativePwm() called.

Parameters:

pos	The position to set the servo between 0.0 and 1.0.

void PWM::SetRaw

(

UINT8

value

)

[virtual]

Set the PWM value directly to the hardware.

Write a raw value to a PWM channel.

Parameters:

value

Raw PWM value. Range 0 - 255.

void PWM::SetSpeed

(

float

speed

)

[protected, virtual]

Set the PWM value based on a speed.

This is intended to be used by speed controllers.

Precondition:

SetMaxPositivePwm() called.

SetMinPositivePwm() called.

SetCenterPwm() called.

SetMaxNegativePwm() called.

SetMinNegativePwm() called.

Parameters:

speed

The speed to set the speed controller between -1.0 and 1.0.

Reimplemented in SafePWM.

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Member Data Documentation

const UINT32 PWM::kDefaultMinPwmHigh = 102 [static, protected]

kDefaultMinPwmHigh is "ticks" where each tick is 6.525us

• There are 128 pwm values less than the center, so...
• The minimum output pulse length is 1.5ms - 128 * 6.525us = 0.665ms
• 0.665ms / 6.525us per tick = 102

const UINT32 PWM::kDefaultPwmPeriod = 774 [static, protected]

kDefaultPwmPeriod is "ticks" where each tick is 6.525us

• 20ms periods (50 Hz) are the "safest" setting in that this works for all devices
• 20ms periods seem to be desirable for Vex Motors
• 20ms periods are the specified period for HS-322HD servos, but work reliably down to 10.0 ms; starting at about 8.5ms, the servo sometimes hums and get hot; by 5.0ms the hum is nearly continuous
• 10ms periods work well for Victor 884
• 5ms periods allows higher update rates for Luminary Micro Jaguar speed controllers. Due to the shipping firmware on the Jaguar, we can't run the update period less than 5.05 ms.

kDefaultPwmPeriod is the 1x period (5.05 ms). In hardware, the period scaling is implemented as an output squelch to get longer periods for old devices.

Set to 5.05 ms period / 6.525us clock = 774

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The documentation for this class was generated from the following files:

• PWM.h
• PWM.cpp