main.cpp

00001 #include "mbed.h"
00002 #include <stdio.h>
00003 #include <stdlib.h>
00004 #include <time.h>
00005 
00006 PwmOut output(D2);
00007 Serial pc(USBTX, USBRX);
00008 
00009 float  random_number;
00010 
00011 void Configure_System_Clocks(void);
00012 
00013 int main() {
00014     
00015     Configure_System_Clocks();
00016     output.period_us(100);  // 100 kHz Period PWM Output
00017     output.write(0.50);    // 50% Duty Cycle
00018     
00019     srand(time(NULL));     // Seed the rand function to intialise it
00020     
00021     while(1){
00022         //random_number = (float)rand()/(float)RAND_MAX;  // Generate random number between 0 and 1
00023         random_number = 0.3;
00024         if(random_number <= 0.5f)
00025         {
00026             output.write(0.5);
00027         }
00028         else
00029         {
00030             output.write(0);
00031         }
00032     }
00033 }
00034 
00035 void Configure_System_Clocks(void){
00036     PWR->CR |= PWR_CR_VOS_1;                                                                    //Voltage scale 2
00037      
00038     RCC->APB1ENR |= RCC_APB1ENR_PWREN;                                              //APB1 Clock power enable
00039     
00040     RCC->CR |= RCC_CR_HSEON;
00041     while((RCC->CR & RCC_CR_HSERDY) == 0){};                                    //Wait for HSE Ready
00042     
00043   //RCC->CFGR |= RCC_CFGR_MCO1PRE_0;        
00044     RCC->CFGR |= RCC_CFGR_MCO1;                                                 //MCO1 OUTPUT = 0=,1=0x02
00045         
00046     FLASH->ACR |= FLASH_ACR_PRFTEN;                                             //Enable Prefetch Buffer
00047     FLASH->ACR |= FLASH_ACR_ICEN;                                                       //Instruction Cache Enable
00048     FLASH->ACR |= FLASH_ACR_DCEN;                                                       //Data Cache Enable
00049     FLASH->ACR |= FLASH_ACR_LATENCY_2WS;                                            //Flash 2 Wait State
00050         
00051     RCC->CFGR |= RCC_CFGR_HPRE_DIV1;                                                //AHB1PRESCALER = HCLK = SYSCLK  1=0x00
00052     RCC->CFGR |= RCC_CFGR_PPRE1_DIV2;                                               //APB1PRESCALER = HCLK/2  2=0x04
00053     RCC->CFGR |= RCC_CFGR_PPRE2_DIV1;                                               //APB2PRESCALER = HCLK/1
00054         
00055     RCC->CR &= ~RCC_CR_PLLON;
00056     
00057   RCC->PLLCFGR = (4ul                       |                // PLL_M =  4
00058                  (84ul << 6)                |                // PLL_N = 84
00059                  (0ul << 16)                |                // PLL_P =  2
00060                  (RCC_PLLCFGR_PLLSRC_HSE)   |                // PLL_SRC = HSE
00061                  (7ul << 24));                               // PLL_Q =   7
00062     
00063     RCC->CR |= RCC_CR_PLLON;                                 // Enable PLL
00064     while((RCC->CR & RCC_CR_PLLRDY) == 0) __NOP();           // Wait till PLL is ready
00065 
00066     RCC->CFGR &= ~RCC_CFGR_SW;                               // Select PLL as system clock source
00067     RCC->CFGR |=  RCC_CFGR_SW_PLL;
00068     while ((RCC->CFGR & RCC_CFGR_SWS) != RCC_CFGR_SWS_PLL);  // Wait till PLL is system clock src
00069     //System clock should be setup for 84MHz, lets output this to MCO1
00070     
00071      
00072     //Setup PA8 MCO1 as GPIO Output 
00073     RCC->AHB1ENR   |= RCC_AHB1ENR_GPIOAEN;                    //Enable GPIOA Clock
00074     GPIOA->MODER   |= GPIO_MODER_MODER8_1;                    //GPIO_MODER_MODER8_1 = 2 = Alternate Function Pin
00075     GPIOA->OTYPER  |= (0ul<<8);                               //Push Pull Output
00076     GPIOA->OSPEEDR |= GPIO_OSPEEDER_OSPEEDR8;                 //High Speed Output
00077     GPIOA->PUPDR     |= (0ul << 2*8);                           //No Pullup Pulldown
00078     GPIOA->AFR[1]  |= (0ul << 0);                                           //AFRH register holds P8-P15 AF Config, 0x00 = AF0 for PORT8 Which from Datasheet Table 9 = MCO1                
00079 }