Diff: main.cpp

Revision:

0:ad3cdc525b99

Child:

1:126dd2f5fc2d

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Tue Jan 31 23:02:02 2017 +0000
@@ -0,0 +1,78 @@
+
+// LAB 3 SAMPLE PROGRAM 1
+
+#include "mbed.h"
+#include "rtos.h"
+
+Ticker tick;                // Ticker for reading analog
+AnalogIn ain(A0) ;          // Analog input
+DigitalOut led1(LED_RED);   // Red LED
+
+Serial pc(USBTX, USBRX); // tx, rx, for debugging
+
+// Message type
+typedef struct {
+  uint16_t analog; /* Analog input value */
+} message_t;
+
+// Mail box
+Mail<message_t, 2> mailbox;
+
+// Function called every 10ms to read ADC
+// Low pass filter  
+// Every 10th value is sent to mailbox
+volatile int samples = 0 ;
+volatile uint16_t smoothed = 0 ; 
+void readA0() {
+    smoothed = (smoothed >> 1) + (ain.read_u16() >> 1) ;
+    samples++ ;
+    if (samples == 10) {
+        // send to thread
+        message_t *mess = mailbox.alloc() ; // may fail but does not block
+        if (mess) {
+            mess->analog = smoothed ;
+            mailbox.put(mess); // fails but does not block if full
+        }
+        samples = 0;
+    }       
+}
+
+// Write voltage digits
+//   v  Voltage as scale int, e.g. 3.30 is 330
+void vToString(int v, char* s) {    
+    s[3] = '0' + (v % 10) ;
+    v = v / 10 ;
+    s[2] = '0' + (v % 10) ;
+    v = v / 10 ;
+    s[0] = '0' + (v % 10) ;
+}
+
+// Main program
+//   Initialise variables
+//   Attach ISR for ticker
+//   Procss messages from mailbox    
+int main() {
+    led1 = 1 ; // turn off 
+    int volts = 0 ;
+    const int threshold = 100 ;
+    int counter = 0 ;
+    char vstring[] = "X.XX\r\n" ;
+
+    tick.attach_us(callback(&readA0), 10000); // ticks every 10ms
+    while (true) {
+        osEvent evt = mailbox.get(); // wait for mail 
+        if (evt.status == osEventMail) {
+            message_t* mess = (message_t*)evt.value.p ;
+            volts = (mess->analog * 330) / 0xffff ;
+            mailbox.free(mess) ;  // free the message space
+            if (volts > threshold) led1 = 0 ; else led1 = 1 ;
+            vToString(volts, vstring) ;
+            counter++ ;
+            if (counter == 10) {  // limit bandwidth of serial
+                pc.printf(vstring) ;
+                counter = 0 ;
+            }
+        }
+
+    }
+}