Andy K / MODSERIAL Featured

Bug fix release

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MODSERIAL is an easy to use library that extends Serial to add fully buffered input and output.

The features of MODSERIAL include:-

/media/uploads/mbedofficial/serial_interfaces.png

Connecting up the MODSERIAL module

The starting point for using MODSERIAL is the Mbed's own handbook for Serial library object. MODSERIAL inherits Serial and adds extensions for buffering. So getting started is easy. Follow the Mbed instructions for Serial to get setup. Here's a reproduction of Serial's simple code starter:-

1  #include "mbed.h"
2
3  Serial pc(USBTX, USBRX); // tx, rx
4 
5  int main() {
6      pc.printf("Hello World!");
7      while(1) {
8          pc.putc(pc.getc() + 1);
9      }
10 }

All we need to do to use MODSERIAL is to add a #include and alter one line thus:-

1  #include "mbed.h"
2  #include "MODSERIAL.h"
3  MODSERIAL pc(USBTX, USBRX); // tx, rx
4 
5  int main() {
6      pc.printf("Hello World!");
7      while(1) {
8          pc.putc(pc.getc() + 1);
9      }
10 }

As we can see, all we have done is add the header at line 2 and changed line 3 to specify the use of MODSERIAL in replacement for Serial. The default settings for MODSERIAL are that both the TX and RX buffers are assigned 256 bytes each of storage space. This storage space is acquired from the heap using malloc.

The default buffer assignment can be manipulated in three ways. First is the compile time setting which alters the default parameters used when creating a MODSERIAL object. This is done thus:-

1  #include "mbed.h"
2
3  #define MODSERIAL_DEFAULT_RX_BUFFER_SIZE 512
4  #define MODSERIAL_DEFAULT_TX_BUFFER_SIZE 1024 
5  #include "MODSERIAL.h"
6
7  MODSERIAL pc(USBTX, USBRX); // tx, rx
8  ...

By defining the two #defines before the #include "MODSERIAL.h" alters the defaults MODSERIAL uses to create it's buffers.

The second method is the run-time version. To get TX at 1024 and RX buffer at 512 as above during run-time initialisation, alter the constructor thus:-

1  #include "mbed.h"
2  #include "MODSERIAL.h"
3
4  // Make TX buffer 1024bytes and RX buffer use 512bytes.
5  MODSERIAL pc(USBTX, USBRX, 1024, 512); // tx, rx
6  ...

If you supply only one numeric value, as shown below, both TX and RX will have the same buffer sizes assigned to them:-

1  #include "mbed.h"
2  #include "MODSERIAL.h"
3
4  // Make both TX and RX use a 512byte buffer.
5  MODSERIAL pc(USBTX, USBRX, 512); // tx, rx
6  ...

The third method is reassigning a new buffer while the program is running. This allows the program to grow and shrink either buffer as required. However, there are caveats to do this as will be shown below.

First, expanding the buffer involves increasing the buffer size. This is fairly straight forward and is accomplished thus:-

1  #include "mbed.h"
2  #include "MODSERIAL.h"
3  MODSERIAL pc(USBTX, USBRX); // tx, rx
4 
5  int main() {
6
7      // Increase the TX buffer from the default 256bytes to 1024bytes.
8      if (pc.txBufferSetSize(1024) != MODSERIAL::Ok) {
9         error("Failed to allocate memory for new buffer");
10     }
11
12     pc.printf("Hello World!");
13     while(1) {
14         pc.putc(pc.getc() + 1);
15     }
16 }

As can be seen, growing the buffer is fairly straight forward. However, how it is done should be understood by the user. First, a new buffer allocation is made using malloc. Once acquired the current buffer is checked for contents. If the current buffer is not empty it is copied to the new buffer so the old buffer contents is maintained after resizing. The last step is then to free() the old memory buffer.

The buffer can also be contracted to a smaller length buffer. Here's the code:-

1  #include "mbed.h"
2  #include "MODSERIAL.h"
3  MODSERIAL pc(USBTX, USBRX); // tx, rx
4 
5  int main() {
6      int result;
7
8      // Decrease the TX buffer from the default 256bytes to 32bytes.
9      result = pc.txBufferSetSize(32);
10     if (result != MODSERIAL::Ok) {
11         switch(result) {
12             case MODSERIAL::BufferOversize: 
13                 error("Contents too big to fit into new allocation");
14                 break;
15             case MODSERIAL::NoMemory: 
16                 error("Not enough memory for new allocation");
17                 break;
18         }
19     }
11
12     pc.printf("Hello World!");
13     while(1) {
14         pc.putc(pc.getc() + 1);
15     }
16 }

Since buffer resizing involves the copying over of any existing old buffer contents the possibility exists that the current buffer contains more bytes than will fit into the new requested buffer. In these conditions the user must handle the return value of the resize functions. If the contents are of no concern then calling txBufferFlush() to empty of the contents before resizing.

MODSERIAL Interrupts

Users of Serial will be familar with the fact that you can attach functions or methods to TxIrq or RxIrq. This attachment of callbacks allows users to have Interrupt Service Routines (ISR) for both the TX and RX channel of the Uart. MODSERIAL uses both of these callbacks to maintain it's buffers and so are not available to users. However, MODSERIAL does contain five potential callbacks the user can use. These are:-

  • TxIrq - This callback is used to inform the user's program that a character was transferred from the TX buffer to the Uart's TX THR FIFO.
  • RxIrq - This callback is used to inform the user's program that a character was transferred from the Uart's RX FIFO RBR to the RX buffer.
  • RxOvIrq - This callback is used to inform the user's program that a character in the Uart's RX FIFO RBR failed to transfer to the RX buffer because the RX buffer was full. The failed byte is availble via xxGetLastChar() methods.
  • TxOvIrq - As RX overflow above
  • TxEmpty - This callback is made when the last byte in the TX buffer is transferred to the Uart's TX THR FIFO. It informs the user's program that the TX buffer has become empty. However, it does not mean transmission is complete. See the example1.cpp example for more information.

Delineating "packets"

Many devices send information on RS232 interfaces in distinct "packets". As an example of this is NMEA information sent by many GPS modules. Each NMEA sentence is delineated by a '\n' newline character. Each sentence can be of vary length depending upon the information being sent, however, all are seperated by a '\n' newline. Detecting this if very simple with MODSERIAL. Here's an example:-

#include "mbed.h"
#include "MODSERIAL.h"

// Connect the TX of the GPS module to p10 RX input
MODSERIAL gps(NC, p10);

bool newline_detected = false;

// Called everytime a new character goes into
// the RX buffer. Test that character for \n
// Note, rxGetLastChar() gets the last char that
// we received but it does NOT remove it from
// the RX buffer.
void rxCallback(MODSERIAL_IRQ_INFO *q) {
    MODSERIAL *serial = q->serial;
    if ( serial->rxGetLastChar() == '\n') {
    	newline_detected = true;
    }
}

int main() {
    gps.baud(9600);
    gps.attach(&rxCallback, MODSERIAL::RxIrq);

    // Wait here until we detect the \n going into the buffer.
    while (! newline_detected ) ;    
    
    // When we get here the RX buffer now contains a NMEA sentence.
    // ...

}

Note, the txGetLastChar() and rxGetLastChar() methods only return the last character but they do not remove that character from the associated buffer.

If this is your first time using MODSERIAL or would just like to test it out then see the example.cpp that comes with the library.



Diff: MODSERIAL.h

Revision:
18:21ef26402365
Parent:
17:6c9b57c14868
Child:
19:a158936322cc
--- a/MODSERIAL.h	Tue Mar 08 01:42:25 2011 +0000
+++ b/MODSERIAL.h	Thu Apr 21 09:20:41 2011 +0000
@@ -45,6 +45,135 @@
 
 namespace AjK {
 
+// Forward reference.
+class MODSERIAL;
+
+/**
+ * @author Andy Kirkham
+ * @see http://mbed.org/cookbook/MODSERIAL
+ * @see example3a.cpp
+ * @see example3b.cpp
+ * @see API 
+ *
+ * <b>MODSERIAL_IRQ_INFO</b> is a class used to pass information (and access to protected
+ * MODSERIAL functions) to IRQ callbacks.
+ */
+class MODSERIAL_IRQ_INFO
+{
+public:
+    friend class MODSERIAL;
+    
+    MODSERIAL *serial;
+    
+    MODSERIAL_IRQ_INFO() { serial = 0; }
+    
+    /** rxDiscardLastChar()
+     *
+     * Remove the last char placed into the rx buffer.
+     * This is an operation that can only be performed
+     * by an rxCallback function. 
+     * @ingroup API
+     * @return The byte removed from the buffer.
+     */
+    int rxDiscardLastChar(void);
+
+protected:
+
+    /** setSerial()
+     *
+     * Used internally by MODSERIAL to set the "this" pointer
+     * of the MODSERIAL that created this object.
+     * @ingroup INTERNAL
+     * @param A pointer to a MODSERIAL object instance.
+     */
+    void setSerial(MODSERIAL *s) { serial = s; }    
+};
+
+// Forward reference dummy class.
+class MODSERIAL_callback_dummy;
+
+/**
+ * @author Andy Kirkham
+ * @see http://mbed.org/cookbook/MODSERIAL
+ * @see example3a.cpp
+ * @see example3b.cpp
+ * @see API 
+ *
+ * <b>MODSERIAL_callback</b> is a class used to hold application callbacks that
+ * MODSERIAL can invoke on certain events.
+ */
+class MODSERIAL_callback 
+{
+protected:
+
+    //! C callback function pointer.
+    void (*c_callback)(MODSERIAL_IRQ_INFO *); 
+    
+    //! C++ callback object/method pointer (the object part).
+    MODSERIAL_callback_dummy *obj_callback;
+    
+    //! C++ callback object/method pointer (the method part).
+    void (MODSERIAL_callback_dummy::*method_callback)(MODSERIAL_IRQ_INFO *);
+
+public:
+    
+    /** Constructor
+     */
+    MODSERIAL_callback() {
+        c_callback      = 0;
+        obj_callback    = 0;
+        method_callback = 0;
+    }
+    
+    /** attach - Overloaded attachment function.
+     *
+     * Attach a C type function pointer as the callback.
+     *
+     * Note, the callback function prototype must be:-
+     * @code
+     * void myCallbackFunction(MODSERIAL_IRQ_INFO *);
+     * @endcode
+     * @param A C function pointer to call.
+     */
+    void attach(void (*function)(MODSERIAL_IRQ_INFO *) = 0) { c_callback = function; }
+    
+    /** attach - Overloaded attachment function.
+     *
+     * Attach a C++ type object/method pointer as the callback.
+     *
+     * Note, the callback method prototype must be:-
+     * @code
+     *     public:
+     *         void myCallbackFunction(MODSERIAL_IRQ_INFO *);
+     * @endcode
+     * @param A C++ object pointer.
+     * @param A C++ method within the object to call.
+     */
+    template<class T> 
+    void attach(T* item, void (T::*method)(MODSERIAL_IRQ_INFO *)) { 
+        obj_callback    = (MODSERIAL_callback_dummy *)item; 
+        method_callback = (void (MODSERIAL_callback_dummy::*)(MODSERIAL_IRQ_INFO *))method; 
+    }
+
+    /** call - Overloaded callback initiator.
+     *
+     * call the callback function.
+     *
+     * @param uint32_t The value to pass to the callback.
+     * @return uint32_t The value the callback returns.
+     */
+    void call(MODSERIAL_IRQ_INFO *arg) {
+        if (c_callback != 0) {
+            (*c_callback)(arg);
+        }
+        else {
+            if (obj_callback  != 0 && method_callback != 0) {
+                (obj_callback->*method_callback)(arg);
+            }
+        }       
+    }    
+};
+
 /**
  * @author Andy Kirkham
  * @see http://mbed.org/cookbook/MODSERIAL
@@ -113,6 +242,9 @@
 {
 public:
 
+    // Allow instances of MODSERIAL_IRQ_INFO to use protected properties and methods.
+    friend class MODSERIAL_IRQ_INFO;
+
     //! A copy of the Serial parity enum
     /** @see http://mbed.org/projects/libraries/api/mbed/trunk/Serial#Serial.format */
     enum Parity {
@@ -231,7 +363,7 @@
      * @param fptr A pointer to a void function, or 0 to set as none
      * @param type Which serial interrupt to attach the member function to (Seriall::RxIrq for receive, TxIrq for transmit buffer empty)
      */  
-    void attach(void (*fptr)(void), IrqType type = RxIrq) { _isr[type].attach(fptr); }
+    void attach(void (*fptr)(MODSERIAL_IRQ_INFO *), IrqType type = RxIrq) { _isr[type].attach(fptr); }
     
     /**
      * Function: attach
@@ -293,8 +425,8 @@
      * @param  type Which serial interrupt to attach the member function to (Seriall::RxIrq for receive, TxIrq for transmit buffer empty)
      */
     template<typename T>
-    void attach(T* tptr, void (T::*mptr)(void), IrqType type = RxIrq) {
-        if((mptr != NULL) && (tptr != NULL)) {
+    void attach(T* tptr, uint32_t (T::*mptr)(uint32_t), IrqType type = RxIrq) {
+        if((mptr != 0) && (tptr != 0)) {
             _isr[type].attach(tptr, mptr);            
         }
     }
@@ -303,15 +435,15 @@
      * @see attach
      * @ingroup API
      */
-    void connect(void (*fptr)(void), IrqType type = RxIrq) { _isr[RxIrq].attach(fptr); }
+    void connect(void (*fptr)(MODSERIAL_IRQ_INFO *), IrqType type = RxIrq) { _isr[RxIrq].attach(fptr); }
     
     /**
      * @see attach
      * @ingroup API
      */
     template<typename T>
-    void connect(T* tptr, void (T::*mptr)(void), IrqType type = RxIrq) {
-        if((mptr != NULL) && (tptr != NULL)) {
+    void connect(T* tptr, void (T::*mptr)(MODSERIAL_IRQ_INFO *), IrqType type = RxIrq) {
+        if((mptr != 0) && (tptr != 0)) {
             _isr[type].attach(tptr, mptr);            
         }
     }
@@ -646,8 +778,28 @@
      */
     int scanf(const char* format, ...);
     #endif
+
+protected:    
+    /**
+     * Used to pass information to callbacks.
+     * @ingroup INTERNALS
+     */
+    MODSERIAL_IRQ_INFO callbackInfo;
+
+    /**
+     * Remove the last char placed into the rx buffer.
+     * This is an operation that can only be performed
+     * by an rxCallback function. To protect the buffers
+     * this function is defined protected so that a 
+     * regular application cannot call it directly. It 
+     * can only be called by the public version within a
+     * MODSERIAL_IRQ_INFO class.
+     * @ingroup INTERNALS
+     * @return The byte removed from the buffer.
+     */
+    int rxDiscardLastChar(void);    
             
-protected:
+private:
 
     /**
      * A pointer to the UART peripheral base address being used.
@@ -713,7 +865,7 @@
      * Callback system.
      * @ingroup INTERNALS
      */
-    FunctionPointer _isr[NumOfIrqTypes];
+    MODSERIAL_callback _isr[NumOfIrqTypes];
     
     /**
      * TX Interrupt Service Routine.
@@ -745,7 +897,7 @@
      * @ingroup INTERNALS
      */
     void enableIrq(void);
-
+    
     /**
      * Get a character from the RX buffer
      * @ingroup INTERNALS
@@ -885,7 +1037,7 @@
      * @param fptr A function pointer to call
      * @return this
      */
-    void attach_dmaSendComplete(void (*fptr)(void)) {  
+    void attach_dmaSendComplete(void (*fptr)(MODSERIAL_IRQ_INFO *)) {  
         _isrDmaSendComplete.attach(fptr);         
     }
     
@@ -898,13 +1050,13 @@
      * @return this
      */
     template<typename T>
-    void attach_dmaSendComplete(T* tptr, void (T::*mptr)(void)) {  
+    void attach_dmaSendComplete(T* tptr, void (T::*mptr)(MODSERIAL_IRQ_INFO *)) {  
         if((mptr != NULL) && (tptr != NULL)) {
             _isrDmaSendComplete.attach(tptr, mptr);         
         }
     }
     
-    FunctionPointer _isrDmaSendComplete;
+    MODSERIAL_callback _isrDmaSendComplete;
     
 protected:    
     /**
@@ -921,7 +1073,7 @@
         if (dma->irqType() == MODDMA::TcIrq)  dma->clearTcIrq();
         if (dma->irqType() == MODDMA::ErrIrq) dma->clearErrIrq();
         dmaSendChannel = -1;
-        _isrDmaSendComplete.call();
+        _isrDmaSendComplete.call(&this->callbackInfo);
         delete(config);
     }