main.cpp

00001 #include "mbed.h"
00002 
00003 #define Fs 1000
00004 #define T (1.0/Fs)
00005 #define PI 3.1415926541
00006 
00007 PwmOut mypwm(PWM_OUT);
00008 
00009 //This GPIO is used for Chip Select
00010 DigitalOut DAC_CS(D10);
00011 
00012 //SPI Object
00013 SPI spi(D11, D12, D13);
00014 
00015 //Ticker for setting the output sampling rate
00016 Ticker t;
00017 
00018 //Discrete time
00019 unsigned int n=0;
00020 
00021 //Frequency f
00022 double f = 10.0;
00023 
00024 //Prototype for the ticker ISR
00025 void writeSample();
00026 
00027 int main() {
00028 
00029     //Set speed of the SPI interface
00030     spi.frequency(20000);
00031     
00032     //16 bit words, mode 0 clock
00033     spi.format(16,0);
00034     
00035     //Write at Fs Hz    
00036     t.attach(writeSample, T);
00037     
00038     while(1) {
00039         sleep();
00040     }
00041 }
00042 
00043 //ISR for ticker
00044 void writeSample()
00045 {
00046     //Enable the selected slave device
00047     DAC_CS = 0;
00048     
00049     //Write a header (top 4 bits) and value (bottom 12 bits) 
00050     double y = cos(2.0*PI*n*f*T);
00051     unsigned int val = (unsigned int)(2048.0 * (y + 1.0));
00052     spi.write(0x7000 | val);
00053     
00054     //Disable the selected slave device (and update the output)
00055     DAC_CS = 1;
00056     
00057     n++;
00058 }