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楼主 |
发表于 2014-11-29 12:38:26
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pwm例程
/*******************************************************************************
Filename: t4_pwm.c
Description: Generates a sine wave signal, by using Timer 4 to generate
a PWM signal with varying duty cycle. The frequency f of the
sine wave is
f = f_tts / (t4_div * 2 * t4_tcv * N)
where f_tts is the Timer tick speed (can be adjusted in the
CLKCON register), t4_div is the Timer 4 prescaler divider value
(can be adjusted in the T4CTL register), t4_tcv is the Timer 4
terminal count value (can be adjusted in the T4CC0 register) and
N is the number of samples per sine wave.
The values for adjusting the PWM duty cycle are stored in a
lookup table, and this value sets the compare value for
Timer 4, which is running in up/down mode, setting output on
compare-up and clearing output on compare-down. The compare
value is changed when Timer 4 reaches 0x00 (and generates an
interrupt).
On the SmartRF05EB, Timer 4 channel 1 is connected to P1_0
(GREEN LED1) for the CC2543EM and CC2545EM and to P1_1
(RED LED2) for the CC2541EM. On the CC2544Dongle Timer 4
channel 1 is connected to P0_2 (g0reen LED). I/O location
alternative 1 is chosen.
This example uses f_tts = 4 Mhz and t4_div = 128, to keep the
pwm period above 120 Hz, to appear smooth to the eye with low
duty cycles. We use N = 16, and t4_tcv = 244 is used to fine
tune a 4 Hz sine wave.
*******************************************************************************/
/*******************************************************************************
* INCLUDES
*/
#include <hal_types.h>
// Include Name definitions of individual bits and bit-fields in the CC254x device registers.
#include <ioCC254x_bitdef.h>
// Include device specific file
#if (chip==2541)
#include "ioCC2541.h"
#elif (chip==2543)
#include "ioCC2543.h"
#elif (chip==2544)
#include "ioCC2544.h"
#elif (chip==2545)
#include "ioCC2545.h"
#else
#error "Chip not supported!"
#endif
/*******************************************************************************
* CONSTANTS
*/
// Number of sine samples.
#define NO_SAMPLES 16
/*******************************************************************************
* LOCAL VARIABLES
*/
/*******************************************************************************
* LOCAL FUNCTIONS
*/
/*******************************************************************************
* @fn t4_isr
*
* @brief Interrupt handler for Timer 4 overflow interrupts. Interrupts from
* Timer 4 are level triggered, so the module interrupt flag is cleared
* prior to the CPU interrupt flag. Timer 4 interrupt source is not
* checked, since only overflow interrupts are enabled. On Timer 4
* overflow interrupts, the PWM duty cycle is changed by altering the
* compare value.
*
* @param void
*
* @return void
*
*******************************************************************************/
#pragma vector = T4_VECTOR
__interrupt void t4_isr(void)
{
/* Local variables. The sine wave consists of 16 samples, so the PWM
* lookup table pwmLut has 16 values. These are calculated from
*
* 121 * cos(k * 2pi/N) + T4CC0/2, k = 0, 1, ..., 15
*
* Since a too large amplitude may saturate the LED or the 8 bit register,
* we attenuate the amplitude by atleast T4CC0/2 - 1.
*/
static uint8 i = 0;
static const uint8 pwmLut[NO_SAMPLES] = {243, 234, 208, 168, 122, 76, 36, 10,
1, 10, 36, 76, 122, 168, 208, 234};
// Clears the module interrupt flag.
T4OVFIF = 0;
/* Writes the PWM value to the compare register and increments the
* index. Writing to the compare register TxCC1 takes effect immediately.
*/
T4CC1 = pwmLut[i++];
if (i == NO_SAMPLES)
{
i = 0;
}
// Clears the CPU interrupt flag.
T4IF = 0;
}
/*******************************************************************************
* @fn main
*
* @brief Configures P1_0 as Timer 4 output, sets up Timer 4 for centre-
* aligned PWM operation and enables overflow interrupts. The rest
* of the program is interrupt driven, so an infinite loop is needed
* after the initialization.
*
* @param void
*
* @return 0
*******************************************************************************/
int main(void)
{
/***************************************************************************
* Setup clock & frequency
*/
// Set global timer tick frequency to 4 MHz
CLKCONCMD = (CLKCONCMD & ~CLKCON_TICKSPD) | CLKCON_TICKSPD_4M;
/***************************************************************************
* Setup peripheral I/O for Timer 4
*/
#if (chip==2541)
// Selects P1_1 as peripheral I/O (RED LED2).
/// P1SEL |= P1SEL_SELP1_1;
#elif (chip==2543 || chip==2545)
// Selects P1_1 as peripheral I/O (GREEN LED1).
P1SEL |= P1SEL_SELP1_0;
#elif (chip==2544)
// Select P0_2 for peripheral function Timer4 on channel 1.
P0SEL1 |= 0x0B;
#endif
#if (chip==2541)
// Timer 4 has priotity over Timer 1.
P2SEL |= P2SEL_PRI1P1;
#elif (chip==2543)
// Set port 1 peripheral priority to Timer 1 over USART0.
PPRI &= ~PPRI_PRI0P1;
#elif (chip==2545)
// Set P1_0 Timer 4 to have priority over Timer 1.
PPRI |= PPRI_PRI0P1;
#endif
#if (chip==2541 || chip==2543 || chip==2545)
// Select Timer 4 pin location as alternative 1
PERCFG &= ~PERCFG_T4CFG;
#endif
/***************************************************************************
* Setup interrupt
*
* Enables global interrupts (IEN0.EA = 1) and interrupts from Timer 4
* (IEN1.T3IE = 1).
*/
EA = 1;
T4IE = 1;
/***************************************************************************
* Timer 4 Setup
*
* Timer 4 channel 1 compare control configuration. Selects the output mode
* so that the output is set on compare-up and cleared on compare-down and
* enables compare mode. This also disables compare interrupts.
*/
T4CCTL1 = T4CCTLn_CMP_SET_CMP_UP_CLR_0 | T4CCTLn_MODE;
/* Timer 4 channel 0 compare value. Sets the Timer 4 terminal count value
* to 244, which makes the Timer count up to 244 before counting down to 0.
* Hence it controls the PWM period and dynamic range.
*/
T4CC0 = 244;
/* Timer 4 channel 1 compare value. Sets the initial compare value to 156
* This value controls the pulse width (duty cycle) and is changed at each
* Timer overflow interrupt.
*/
T4CC1 = 156;
/* Timer 4 control. Sets the prescaler divider value to 128, starts the Timer,
* enables overflow interrupts, clears the Timer and sets the mode to
* up-down.
*/
T4CTL = T4CTL_DIV_128 | T4CTL_START | T4CTL_OVFIM |
T4CTL_CLR | T4CTL_MODE_UPDOWN;
// Infinite loop.
while (1);
} |
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