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oPWM Class Reference

A class implementing a pulse width modulator using the Queued output match (QOM) function of the TPU. More...

#include <opwm.h>

Public Member Functions
MICROSECOND	get_hightime (void)
	return current high time [DOS only]
MICROSECOND	get_lowtime (void)
	return current low time [DOS only]
void	WSwrite (void)
	Write object to simulator.
void	hightime (MICROSECOND high)
	Hightime set the on time for the pulse measured in micro-seconds.
void	nexthigh (MICROSECOND high)
	Used when oPWM is not operating to set new hightime when activated.
void	lowtime (MICROSECOND low)
	Lowtime is the off time for the pulse measured in micro-seconds.
void	nextlow (MICROSECOND low)
	Used when oPWM is not operating to set new lowtime when activated.
void	priority (PRIORITY p)
	Sets the TPU channel execution priority (Ref. TPU Channel Utilization). Default MIDDLE_PRIORITY.
void	value (bool onoff) const
	For oDO1_TPU.
Static Public Member Functions
int	TCR1 (void)
void	TMCR (int iarb)
bool	HSQR (int chan, int val)
	Configures the host sequence register.
bool	HSRR (int chan, int val)
	Configures the host sequence request register.
bool	CPR (int chan, int val)
	Configures the channel priority register (Ref. TPU Channel Utilization).
bool	CIER (int chan, int cie)
	Configures the channel interrupt enable register.
int	CISR (int chan)
	Returns the channel interrupt status register.
void	CISR_clear (int chan)
	Clears the channel interrupt status register for the channel.
bool	TICR (int cirl, int cibv)
	Configures the TPU interrupt configuration register.
int	tpu_vector (IOLINE channel)
	Given a channel, returns the vector number to use for an interrupt.

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Detailed Description

A class implementing a pulse width modulator using the Queued output match (QOM) function of the TPU.

Operation

The oPWM is implemented using the queued output match function (QOM) of the TPU. The 68322 PWM speed is derived from two sources:

• System clock speed
• Prescaler of system clock into the TPU

Remarks

The oPWM object can generate speeds as low as one micro-second.

Note:

Officially, the MRM periodic interrupt timer can go as low as 250 nano-seconds.

The maximum limit upon the PWM is dependent upon the setting of the TPU TCR1P (clock prescaler). The default setting for the prescaler is 32 (Ref. TPU). This allows a maximum of about 64 milli-seconds at 16 MHz. To generate a pulse beyond that requires setting the TPU TCR1P to 256 which allows a maximum of about 1 second.

It is important to understand the relationship between the number of clocks (TCR1P/PSCK) and the internal system clock to obtain the value for the high and low time; we see from the TPU reference manual 2-2 that the number of clocks required to generate a 1 microsecond pulse is 16 clocks at 16 MHz. Therefore, at 8 MHz, the clock is twice as slow which means it takes twice as many (32) clocks per micro second. Similarly if the prescaler is increased, this decreases the effective clock time on the TPU channel. Thus the higher the TPU effective system clock rate, the more clocks I would need to generate to get my 1 microsecond. Finnally, ignoring the round off of integer division, I thus obtain:

value = time_desired*(clock_frequency/number_clocks) example: scale_factor = (.0015 seconds)*(25000000 /32)

or if you divide everything by 1,000,000 since clock_frequency is in millions (rounded to 8,16, or 25MHz) then we can specify the time in one millionth of a second (microseconds). I have since replaced the simple clock_frequency definitions with more accurate float math versions. I felt the bloat was worth it :)

Sample Code

#include <hardware/opwm.h>
int main()
{
oPWM pwm(14);
// Generate 1.5 milli-second high time with 8 millisecond lowtime (period 9.5 milliseconds).
  pwm.hightime(1500);  
  pwm.lowtime(8000);
  pwm.operate(true);
}

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Member Function Documentation

bool CIER (  int  chan, int  cie )  [static, inherited]

Configures the channel interrupt enable register. Parameters: int:  channel int:  1 enables; 0 disables

bool CPR (  int  chan, int  val )  [static, inherited]

Configures the channel priority register (Ref. TPU Channel Utilization). Parameters: int:  channel int:  priority

bool HSQR (  int  chan, int  val )  [static, inherited]

Configures the host sequence register. Parameters: int:  channel int  dependent upon function (CFSR) selected

bool HSRR (  int  chan, int  val )  [static, inherited]

Configures the host sequence request register. Parameters: int:  channel int:  dependend upon function

void nexthigh (  MICROSECOND  high  )  [inherited]

Used when oPWM is not operating to set new hightime when activated. DCmotor (and maybe like objects) needs this, because the only way to stop the PWM (that I know of) is to set hightime to 0--thus loosing the previous value of hightime. thus if you set the hightime while the object is non-operational, you want it to be set to that value the next time the object goes operational (see dcmotor.cpp to know what I'm talking about).

int TCR1 (  void   )  [static, inherited]

misnomer--should be TCR1 divisor--return number of clocks (PSCK,TCR1P modifications) Globally available object. Can be used in combination with TPU_REGISTER definition to say TPU_REGISTER->CFSR.BITS...

void TMCR (  int  iarb  )  [static, inherited]

was tpu_init Configures the channel function select register

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

• opwm.h

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