SFBHWPWM.h File Reference

Support for h/w-based Pulse Width Modulation. More...

#include "SFBTypes.h"

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Enumerations
enum	PWMChannelModes {   PWM_INACTIVE,   PWM_SINGLE_EDGE,   PWM_DOUBLE_EDGE,   PWM_CHANNEL_MODES_MAX }
	The operational modes of a PWM channel. More...
enum	PWMIndices {   PWM_BODY_RGB_RED_PIN,   PWM_BODY_RGB_GREEN_PIN,   PWM_BODY_RGB_BLUE_PIN,   PWM_NORTH_LED_PIN,   PWM_SOUTH_LED_PIN,   PWM_EAST_LED_PIN,   PWM_WEST_D0_PIN,   PWM_WEST_D2_PIN,   PWM_WEST_D3_PIN,   PWM_EAST_D1_PIN,   PWM_EAST_D3_PIN }
	The possible 'pwmIndex' values. More...
Functions
void	PWMStart ()
	Power up, initialize and activate the PWM block.
void	PWMStop ()
	Deactivate and power down the PWM blcok.
void	PWMSetMode (u32 pwmIndex, u32 mode)
	Set the operating mode of (the channel of) a PWM-capable pin.
void	PWMSetWidth (u32 pwmIndex, u32 width, bool commit=true)
	Sets the duty cycle of (the channel of) a PWM-capable pin.
u32	PWMGetWidth (u32 pwmIndex)
	Gets the current pulse width a PWM-active pin.
int	PWMFindIndex (int sfbPin)
	Find the PWMIndices value corresponding to a given sfbPin.
u32	PWMGetPin (u32 pwmIndex)
	Given a legal PWMIndices value, this method returns the SFB pin number of the corresponding pin.
u32	PWMGetChannel (u32 pwmIndex)
	Given a legal PWMIndices value, this method returns the PWM 'channel number' of the corresponding pin.

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Detailed Description

Support for h/w-based Pulse Width Modulation.

See the LPC23xx user manual (lpc23xx_um.pdf) Chapter 24 for details of operation

Author:

David H. Ackley.

Date:

(C) 2009 All rights reserved.

Code License:

The GNU Lesser General Public License

License Note:

All code samples shown in documentation are placed into the public domain.

---

Enumeration Type Documentation

enum PWMChannelModes

The operational modes of a PWM channel.

All channels start out as PWM_INACTIVE.

Enumerator:

PWM_INACTIVE	Channel unused.
PWM_SINGLE_EDGE	Single-edge mode (Channel on at 1, off at PWMSetWidth time).
PWM_DOUBLE_EDGE	Double-edged mode (see LPC23xx manual for details).

enum PWMIndices

The possible 'pwmIndex' values.

The h/w PWM system can generate pulses on up to six different pins simultaneously, and each of the six pulse widths can be controlled individually. In calls to the PWM methods, these indices specify which pwmIndex -- and thus which pin -- is to be affected. Note there are only six 'PWM channels', but there are 12 possible values listed here -- this is because each channel can be routed to more than one pin, if desired. On the flip side, that means certain pairs of pins listed here cannot have different pulse widths when used with h/w PWM.

For example, consider the following sequence

      PWMStart();

      PWMSetMode(PWM_NORTH_LED_PIN,PWM_SINGLE_EDGE);   // Fire up PWM on North LED
      PWMSetWidth(PWM_NORTH_LED_PIN, 7000);            // Set North LED to 30% brightness (70% high==off)

      PWMSetMode(PWM_WEST_D2_PIN,PWM_SINGLE_EDGE);     // Also, fire up West D2 for a servo
      PWMSetWIdth(PWM_WEST_D2_PIN, 750);               // Set West D2 to 1500usec width

      pprintf("L N=%d\n",PWMGetWidth(PWM_NORTH_LED_PIN));  // Unexpectedly prints 'L N=750'!  

in which changing one width (that of PWM_WEST_D2_PIN) causes an apparently unrelated width (that of PWM_NORTH_LED_PIN) to change. Why does it happen? Because PWMGetChannel(PWM_NORTH_LED_PIN) and PWMGetChannel(PWM_WEST_D0_PIN) are both equal to 4. See PWMGetChannel for details.

Enumerator:

PWM_BODY_RGB_RED_PIN	PWM the RGB Red LED.
PWM_BODY_RGB_GREEN_PIN	PWM the RGB Green LED.
PWM_BODY_RGB_BLUE_PIN	PWM the RGB Blue LED.
PWM_NORTH_LED_PIN	PWM the North LED.
PWM_SOUTH_LED_PIN	PWM the South LED.
PWM_EAST_LED_PIN	PWM the East LED.
PWM_WEST_D0_PIN	PWM the West D0 pin.
PWM_WEST_D2_PIN	PWM the West D2 pin.
PWM_WEST_D3_PIN	PWM the West D3 pin.
PWM_EAST_D1_PIN	PWM the East D1 pin.
PWM_EAST_D3_PIN	PWM the East D3 pin.

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Function Documentation

int PWMFindIndex

(

int

sfbPin

)

Find the PWMIndices value corresponding to a given sfbPin.

Not all SFB pins are capable of h/w supported PWM operation; those that are all have values assigned in PWMIndices. This finds the PWMIndices value of a given sfbPin if it exists

Parameters:

sfbPin

Pin number to search for its corresponding PWMIndices value.

Returns:

The PWMIndices value corresponding to sfbPin, or -1 if sfbPin is not capable of h/w supported PWM.

u32 PWMGetChannel

(

u32

pwmIndex

)

Given a legal PWMIndices value, this method returns the PWM 'channel number' of the corresponding pin.

For reference, the assignment of PWMIndices to channels is:

PWM channel number	Associated PWMIndices
1	BODY_RGB_GREEN_PIN
2	BODY_RGB_RED_PIN, WEST_D0_PIN
3	BODY_RGB_BLUE_PIN, WEST_D3_PIN
4	NORTH_LED_PIN, WEST_D2_PIN
5	SOUTH_LED_PIN, EAST_D1_PIN
6	EAST_LED_PIN, EAST_D3_PIN

Parameters:

pwmIndex

The PWMIndices value

Returns:

A PWM channel number, in the range of 1..6.

Blinks:

E_API_MAX_RANGE if pwmIndex is not in the PWMIndices range

u32 PWMGetPin

(

u32

pwmIndex

)

Given a legal PWMIndices value, this method returns the SFB pin number of the corresponding pin.

Parameters:

pwmIndex

The PWMIndices value

Returns:

The SFB pin number used by this PWMIndices value.

Blinks:

E_API_MAX_RANGE if pwmIndex is not in the PWMIndices range

u32 PWMGetWidth

(

u32

pwmIndex

)

Gets the current pulse width a PWM-active pin.

Returns a value in the same units as set in PWMSetWidth.

Parameters:

pwmIndex

one of the PWMIndices values, denoting the PWM-capable pin of interest

Blinks:

E_API_MAX_RANGE if pwmIndex is not in the PWMIndices range

void PWMSetMode	(	u32	pwmIndex,
		u32	mode
	)

Set the operating mode of (the channel of) a PWM-capable pin.

If the mode is PWM_INACTIVE, that pin's mode is set to REFLEX_MODE, otherwise is it set to HW_MODE and the relevant PWM registers are configured as specified. After PWMSetMode is used with a mode other than PWM_INACTIVE, PWMSetWidth should be used to specify the duty cycle of the pulse.

Parameters:

	pwmIndex	one of the PWMIndices values, denoting the PWM-capable pin of interest
	mode	one of the PWMChannelModes values, specifiying how the associated channel will act

Blinks:

E_API_MAX_RANGE if pwmIndex is not in the PWMIndices range

Blinks:

E_API_MAX_RANGE if mode is not in the PWMChannelModes range

void PWMSetWidth	(	u32	pwmIndex,
		u32	width,
		bool	commit = true
	)

Sets the duty cycle of (the channel of) a PWM-capable pin.

The repetition rate of the PWM is 50Hz, producing a 20,000 usecs period. width is in the range of 1..10000 and is in units of 2usecs or 0.01% of maximum width. For example, width values of 500-1000 produce pulse times of 1ms-2ms (the typical full-throw range of servo pulses), and a width of 10000 produces a 50% duty cycle pulse. Optional argument commit determines whether to 'release' this width change now. If commit is specified and false, this width change will not take effect until the next PWMSetWidth with commit unspecified or set to true. If a number of widths should be changed simultaneously, use commit equals false on all but the last call.

Parameters:

	pwmIndex	one of the PWMIndices values, denoting the PWM-capable pin of interest
	width	number of 2usec units one of the PWMChannelModes values, specifiying how the associated channel will act
	commit	whether this change should take effect ASAP or be deferred.

Blinks:

E_API_MAX_RANGE if pwmIndex is not in the PWMIndices range