Bug fix release

Dependents:   AntiTheftGPS XbeeReceive XbeeSend Superball_Ball2 ... more

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.



Committer:
AjK
Date:
Mon Nov 22 09:58:34 2010 +0000
Revision:
8:775f860e94d3
Parent:
6:c8f77fe1cc10
Child:
9:b3cdae80e7a9
1.8

Who changed what in which revision?

UserRevisionLine numberNew contents of line
AjK 0:eb2522b41db8 1 /*
AjK 0:eb2522b41db8 2 Copyright (c) 2010 Andy Kirkham
AjK 0:eb2522b41db8 3
AjK 0:eb2522b41db8 4 Permission is hereby granted, free of charge, to any person obtaining a copy
AjK 0:eb2522b41db8 5 of this software and associated documentation files (the "Software"), to deal
AjK 0:eb2522b41db8 6 in the Software without restriction, including without limitation the rights
AjK 0:eb2522b41db8 7 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
AjK 0:eb2522b41db8 8 copies of the Software, and to permit persons to whom the Software is
AjK 0:eb2522b41db8 9 furnished to do so, subject to the following conditions:
AjK 0:eb2522b41db8 10
AjK 0:eb2522b41db8 11 The above copyright notice and this permission notice shall be included in
AjK 0:eb2522b41db8 12 all copies or substantial portions of the Software.
AjK 0:eb2522b41db8 13
AjK 0:eb2522b41db8 14 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
AjK 0:eb2522b41db8 15 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
AjK 0:eb2522b41db8 16 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AjK 0:eb2522b41db8 17 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
AjK 0:eb2522b41db8 18 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
AjK 0:eb2522b41db8 19 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
AjK 0:eb2522b41db8 20 THE SOFTWARE.
AjK 0:eb2522b41db8 21 */
AjK 0:eb2522b41db8 22
AjK 0:eb2522b41db8 23 #include "MODSERIAL.h"
AjK 0:eb2522b41db8 24 #include "MACROS.h"
AjK 0:eb2522b41db8 25
AjK 0:eb2522b41db8 26 namespace AjK {
AjK 0:eb2522b41db8 27
AjK 0:eb2522b41db8 28 int
AjK 0:eb2522b41db8 29 MODSERIAL::__putc(int c, bool block) {
AjK 0:eb2522b41db8 30
AjK 8:775f860e94d3 31 // If no buffer is in use fall back to standard TX FIFO usage.
AjK 8:775f860e94d3 32 // Note, we must block in this case and ignore bool "block"
AjK 8:775f860e94d3 33 // so as to maintain compat with Mbed Serial.
AjK 8:775f860e94d3 34 if (buffer[TxIrq] == (char *)NULL || buffer_size[TxIrq] == 0) {
AjK 8:775f860e94d3 35 while (! MODSERIAL_THR_HAS_SPACE) ; // Wait for space in the TX FIFO.
AjK 8:775f860e94d3 36 _THR = (uint32_t)c;
AjK 8:775f860e94d3 37 return 0;
AjK 8:775f860e94d3 38 }
AjK 8:775f860e94d3 39
AjK 8:775f860e94d3 40 if ( MODSERIAL_THR_HAS_SPACE && MODSERIAL_TX_BUFFER_EMPTY ) {
AjK 4:28de979b77cf 41 _THR = (uint32_t)c;
AjK 4:28de979b77cf 42 }
AjK 4:28de979b77cf 43 else {
AjK 8:775f860e94d3 44 if (block) {
AjK 8:775f860e94d3 45 while ( MODSERIAL_TX_BUFFER_FULL ) { // Blocks!
AjK 8:775f860e94d3 46 // If putc() is called from an ISR then we are stuffed
AjK 8:775f860e94d3 47 // because in an ISR no bytes from the TX buffer will
AjK 8:775f860e94d3 48 // get transferred to teh TX FIFOs while we block here.
AjK 8:775f860e94d3 49 // So, to work around this, instead of sitting in a
AjK 8:775f860e94d3 50 // loop waiting for space in the TX buffer (which will
AjK 8:775f860e94d3 51 // never happen in IRQ context), check to see if the
AjK 8:775f860e94d3 52 // TX FIFO has space available to move bytes from the
AjK 8:775f860e94d3 53 // TX buffer to TX FIFO to make space. The easiest way
AjK 8:775f860e94d3 54 // to do this is to poll the isr_tx() function while we
AjK 8:775f860e94d3 55 // are blocking.
AjK 8:775f860e94d3 56 isr_tx(false);
AjK 5:8365c4cf8f33 57 }
AjK 8:775f860e94d3 58 }
AjK 8:775f860e94d3 59 else if( MODSERIAL_TX_BUFFER_FULL ) {
AjK 8:775f860e94d3 60 buffer_overflow[TxIrq] = c; // Oh dear, no room in buffer.
AjK 8:775f860e94d3 61 _isr[TxOvIrq].call();
AjK 8:775f860e94d3 62 return -1;
AjK 0:eb2522b41db8 63 }
AjK 8:775f860e94d3 64 buffer[TxIrq][buffer_in[TxIrq]] = c;
AjK 8:775f860e94d3 65 buffer_count[TxIrq]++;
AjK 8:775f860e94d3 66 buffer_in[TxIrq]++;
AjK 8:775f860e94d3 67 if (buffer_in[TxIrq] >= buffer_size[TxIrq]) {
AjK 8:775f860e94d3 68 buffer_in[TxIrq] = 0;
AjK 8:775f860e94d3 69 }
AjK 8:775f860e94d3 70 _IER |= 0x2;
AjK 0:eb2522b41db8 71 }
AjK 4:28de979b77cf 72
AjK 0:eb2522b41db8 73 return 0;
AjK 0:eb2522b41db8 74 }
AjK 0:eb2522b41db8 75
AjK 0:eb2522b41db8 76 }; // namespace AjK ends