Content originally posted in LPCWare by ucniranjan on Wed Jan 22 04:56:32 MST 2014
Friends,
I am using the LPCXpresso 812 Board with the IDE. I have a simple program, wherein I initialize the SCT as a PWM timer, with 1/3 duty cycle. The SCT spec: 12MHz clock, 16-bit counter, 2 events and interrupt mode. I redirect the SCT output to pin 7. The main function instantiates
PWM bursts of 20 pulses. When I run the code below, and connect the Logic Analyzer to pin 7, I do not see the PWM pulses. What could be wrong? I feel I am missing somethin in initializing the SCT. I have used the default libraries of LPCXpresso.
Thanks,
Niranjan
/****************************************************************************
Main Function
****************************************************************************/
#ifdef __USE_CMSIS
#include "LPC8xx.h"
#endif
#include "lpc8xx_clkconfig.h"
#include "lpc8xx_gpio.h"
static volatile uint32_t PWMCount = 0;
void SCT_IRQHandler(void)
{
PWMCount--;
if(PWMCount == 0)
{
LPC_SCT->CTRL_L |= (1 << 2);
}
LPC_SCT->EVFLAG = (1 << 0);
}
void PWM_SCT_Init(void)
{
LPC_SYSCON->SYSAHBCLKCTRL |= (1 << 8); // SCT clock
LPC_SYSCON -> PRESETCTRL &= ~(0x1<<8);
LPC_SYSCON -> PRESETCTRL |= (0x1<<8);
LPC_SCT->CONFIG |= (1 << 17); // Two 16-bit timers, auto limit
LPC_SCT->CTRL_L |= (SystemCoreClock/12000000-1) << 5; // SCT clock = 12 MHz
LPC_SCT->MATCH[0].L = 360; // match 0 @ 30 usec
LPC_SCT->MATCHREL[0].L = 360;
LPC_SCT->MATCH[1].L = 240; // match 1 @ 20 usec
LPC_SCT->MATCHREL[1].L = 240;
LPC_SCT->EVENT[0].STATE = 0x00000001; // event 0 only happens in state 0
LPC_SCT->EVENT[0].CTRL = (0 << 0) | // MATCHSEL[3:0] = related to match 0
(1 << 12) | // COMBMODE[13:12] = match condition only
(1 << 14) | // STATELD[14] = STATEV is loaded into state
(0 << 15); // STATEV[15] = 0
LPC_SCT->EVENT[1].STATE = 0x00000001; // event 1 only happens in state 0
LPC_SCT->EVENT[1].CTRL = (1 << 0) | // MATCHSEL[3:0] = related to match 1
(1 << 12) | // COMBMODE[13:12] = match condition only
(1 << 14) | // STATELD[14] = STATEV is loaded into state
(0 << 15); // STATEV[15] = 0
LPC_SCT->EVEN = (1 << 0);
NVIC_EnableIRQ(SCT_IRQn); // enable SCT interrupt
NVIC_SetPriority(SysTick_IRQn, 3); // Give less priority to SysTick_IRQn
}
void Start_PWM(uint32_t pwmcount)
{
PWMCount = pwmcount;
LPC_SCT->CTRL_L &= ~(1 << 2); // unhalt SCT
while(PWMCount)
{
LPC_SCT->OUT[0].CLR = (1 << 0); // event 0 will set SCT_OUT_0, SETCLR0 = 0
LPC_SCT->OUT[0].SET = (1 << 1); // event 1 will clear SCT_OUT_0, SETCLR0 = 0
}
}
/* Main Program */
int main (void) {
uint32_t regVal;
SystemCoreClockUpdate();
/* Config CLKOUT, mostly used for debugging. */
regVal = LPC_SWM->PINASSIGN8 & ~( 0xFF << 16 );
LPC_SWM->PINASSIGN8 = regVal | ( 12 << 16 );
CLKOUT_Setup( CLKOUTCLK_SRC_MAIN_CLK );
LPC_SWM->PINASSIGN6 = 0x07FFFFFF; // SCT OUTP_0 at P0.7
PWM_SCT_Init();
int i1;
while(1)
{
Start_PWM(20);
for (i1=0; i1<100000; i1++) { __NOP(); }
}
}
