main.cpp

00001 //
00002 //  CLOCK OUT to PWM1[6] Sample with Freq Counter using Cap2.0 
00003 //  For LPC1768-mbed
00004 //
00005 //  Reference: 5MHz Clock Out Code and Comment - http://mbed.org/forum/mbed/topic/733/
00006 //
00007 //  !! To Self Measurement Output Clock, Connect p21 <-> p30 with jumper wire.
00008 //  2013.6.18 : Wrong comment about MR6 and Duty fix.
00009 //
00010 
00011 #include "mbed.h"
00012 
00013 PwmOut fmclck(p21);     // for RESERVE pin21 as PWM1[6]
00014 DigitalIn clkin(p30);   // for RESERVE pin30 as CAP2[0]
00015 
00016 // Reset Counter and Count Start
00017 void P30_RESET_CTR(void)
00018 {
00019     LPC_TIM2->TCR = 2;             // Reset the counter (bit1<=1,bit0<=0)
00020     LPC_TIM2->TCR = 1;             // UnReset counter (bit1<=0,bit0<=1)
00021 }
00022 
00023 // Get Counter Value
00024 int P30_GET_CTR(void)
00025 {
00026     return LPC_TIM2->TC; // Read the counter value
00027 }
00028 
00029 // Setting p30 to Cap2.0
00030 void P30_INIT_CTR(void)
00031 {
00032     LPC_SC->PCONP |= 1 << 22;               // 1)Power up TimerCounter2 (bit22)
00033     LPC_PINCON->PINSEL0 |= 3 << 8;          // 2)Set P0[4] to CAP2[0]
00034     LPC_TIM2->TCR = 2;                          // 3)Counter Reset (bit1<=1,bit0<=0)
00035     LPC_TIM2->CTCR = 1;                     // 4)Count on riging edge Cap2[0]
00036     LPC_TIM2->CCR = 0;                                          // 5)Input Capture Disabled
00037     LPC_TIM2->TCR = 1;                          // 6)Counter Start (bit1<=0,bit0<=1)
00038 }
00039 
00040 // Clock Output From pin21(PWM6)
00041 // Set Clock Freq with div.
00042 // if mbed is running at 96MHz, div is set 96 to Get 1MHz.
00043 void PWM6_SETCLK(int div)
00044 {
00045     LPC_PWM1->TCR = (1 << 1);               // 1)Reset counter, disable PWM
00046     LPC_SC->PCLKSEL0 &= ~(0x3 << 12);  
00047     LPC_SC->PCLKSEL0 |= (1 << 12);          // 2)Set peripheral clock divider to /1, i.e. system clock
00048     LPC_PWM1->MR0 = div - 1;                // 3)Match Register 0 is shared period counter for all PWM1
00049     LPC_PWM1->MR6 = (div + 1)>> 1;          // 
00050     LPC_PWM1->LER |= 1;                     // 4)Start updating at next period start
00051     LPC_PWM1->TCR = (1 << 0) || (1 << 3);   // 5)Enable counter and PWM    
00052 }
00053 
00054 int main() {        
00055     PWM6_SETCLK(19) ; // Outout mbed's "PWM6" pin to 96MHZ/19 = 5.052MHz (Approx)
00056     // PWM6_SETCLK(96) ; // Outout mbed's "PWM6" pin to 96MHZ/96 = 1.000MHz (Approx)
00057     P30_INIT_CTR();
00058     while(1){
00059         P30_RESET_CTR();
00060         wait_us(100000); // Gate time for count
00061         printf("pin30 Freq = %u (Hz)\r\n",P30_GET_CTR());
00062     }
00063 }