Diff: main.cpp

Revision:

3:f04c8a88a27d

Parent:

2:4857a7cbb9da

Child:

4:42b85520dca6

--- a/main.cpp	Wed Jan 23 17:56:08 2019 +0000
+++ b/main.cpp	Mon Feb 04 16:11:54 2019 +0000
@@ -2,6 +2,10 @@
 // -----------------------
 // Periodically write to the AnalogOut to create a sine wave
 // Alternate between two fixed frequencies every 30 sec
+// 
+// This code uses the Ticker API to create a periodic interrupt
+// Devices used in this way must not call locks; a variant of 
+//   the AnalogOut device w/o locking is created for this
 //
 // THIS VERSION HAS DEBUGGING CODE USING THE SERIAL PORT
 
@@ -10,11 +14,25 @@
 #include "mbed.h"
 #include "sineTable.h"
 
+// --------------------------
+// This declaration introduces a derived version of the mbed AnalogOut
+//   class with the locking removed.
+// You do NOT NEED TO UNDERSTAND this 
+class AnalogOut_unsafe : public AnalogOut {
+  public:
+    AnalogOut_unsafe (PinName pin) : AnalogOut (pin) {} 
+  protected: 
+    virtual void lock() {}
+    virtual void unlock() {}
+};
+// --------------------------
+
 Ticker tick ;          // Creates periodic interrupt
-AnalogOut ao(PTE30) ;  // Analog output
+AnalogOut_unsafe ao(PTE30) ;  // Analog output
 
 // --- following code for debugging ---
 Thread debugT ;
+EventFlags event_flags;
 Serial pc(USBTX, USBRX); // tx, rx, useful for debugging
 
 // Put a simple representation of the sine wave
@@ -24,14 +42,14 @@
     pc.putc('*') ;
     while (sine4--) pc.putc('*') ;
     pc.putc('\n') ;
-    //pc.putc('\r') ;  
+    pc.putc('\r') ;  // depends on the OS being used
 }
 
 volatile int index = 0 ; // this variable is not just for debugging!!
 
 void debugCallback() {
     while (true) {
-        Thread::signal_wait(0x1) ;
+        event_flags.wait_any(0x1) ;
         debug(index) ;  // there is a race condition here
     }
 }
@@ -41,7 +59,7 @@
 // Write new value to AnalogOut 
 void writeAout() {
     ao.write_u16(sine[index]) ;
-    debugT.signal_set(0x1) ; // DEBUGGING low frequency only
+    event_flags.set(0x1) ; // DEBUGGING low frequency only
     index = (index + 1) % 64 ;   
 }