RngLib

Revision as of 07:55, 28 March 2009

rngLib - an implementation of vxWorks style ring buffers

What is this?

Ring buffers work like any first in first out buffers (FIFOs), except are implemented in software. They may be used to store data such as catching keypresses, serial or other data while the system is busy which may then be read out later in the exact order it was received into the buffer. They are interrupt safe so long as data is read out before the buffer 'fills'. In this way ring buffers are perfect for storing data of various lengths that is received faster than may be immediately processed.

The functions here are pretty self explanatory. thdslib provides for byte and/or 32bit word sized ring buffers. These may be used in addition to the FIFO or anyplace you need more code.

rngLib is based on the VxWorks implementation of the same name and are intended to be compatible. The functions may just as easily be used on any system as well as the NDS, with only slight modifications (mostly change the bool data type to what the system expects).

Where to get it

Currently the sources for this are part of LibThds. The source can be downloaded via SVN (see libthds page) or directly from the svn httpd:

• rngLib.c
• rngLib.h

32bit buffer versions:

• rng32Lib.c
• rng32Lib.h

Functions

todo: Explain these in detail! rngCreate
Creates a new ring buffer instance

• nbytes - number to bytes (or 32 bit words for thFifo32) to be allocated for this buffer. Directly represents how much data the buffer can hold.

RING_ID rngCreate(int nbytes);

rngDelete
Deletes a ring buffer instance

• ringId - object of type RING_ID to be destroyed

void rngDelete(RING_ID ringId);

rngNBytes

• ringId - object of type RING_ID

Returns the number of bytes (or 32 bit words for thFifo32) that have been placed into the ring buffer

int rngNBytes(RING_ID ringId);	//rngNBytes( ) - determine the number of bytes available in a ring buffer

rngFlush
Removes all content from ring buffer.

• ringId - object of type RING_ID

void rngFlush(RING_ID ringId);  //empty all buffer content,

rngBufGet
Retrieves data, if available, from ring buffer.

• ringId - object of type RING_ID
• buffer - point to buffer to contain data
• maxbytes - maximum number of bytes to be read

int rngBufGet(RING_ID rngId, char *buffer, int maxbytes);  //get number of chars, retuns nbytes gotten

rngBufPut

• ringId - object of type RING_ID
• buffer - pointer to buffer containing data to be placed into buffer
• nbytes - number of bytes to place into buffer, usually the length of buffer.

Returns the number of bytes actually written to the buffer. If buffer is full will return 0.

int rngBufPut(RING_ID rngId, char *buffer, int nbytes); //write a number of chars, returns nbytes put

rngIsEmpty
Test if ring buffer contains data

• ringId - object of type RING_ID

Returns true if ring buffer is empty, otherwise false.

bool rngIsEmpty(RING_ID ringId); //tst if buffer is empty

rngCreate
Test if ring buffer is at maximum capacity

• ringId - object of type RING_ID

Returns true if buffer is full, otherwise false

bool rngIsFull(RING_ID ringId);  //tst if full

rngFreeBytes/rng32FreeWords

• ringId - object of type RING_ID

Returns an integer indicating the maximum number of bytes (or 32 bit words for thFifo32) that may be placed in buffer before it is full.

int rngFreeBytes(RING_ID ringId); //how many free bytes remain?

rngNBytes/rng32NWords
Number of bytes bytes (or 32 bit words for thFifo32) that may be gotten from the ring buffer

• ringId - object of type RING_ID

Returns number of bytes (or 32 bit words for thFifo32) that may be retrieved from buffer

int rngNBytes(RING_ID ringId);

rngPutAhead
Put a single byte into ring buffer without incrementing count. rngFreeBytes, rngIsFull, or rngIsEmpty should probably be used for most cases to first determine that placing a character into the buffer will not result in overflow.

• ringId - object of type RING_ID
• byte - single character (or 32bit word for thFifo32) to be placed into buffer
• offset - where to store the data, 0 would be at first, 1 would be the character after 0, 2 would be two characters ahead, etc etc

void rngPutAhead(RING_ID ringId, char byte, int offset); //put byte in the read buffer without incrementing counter

rngMoveAhead
Used in conjunction with (usually after) rngPutAhead, will increment the number of characters (or 32bit words for thFifo32) specified.

• ringId - object of type RING_ID
• n - number of bytes (or 32bit words for thFifo32) to increment fifo counter. Usually the number of bytes placed into the buffer using rngMoveAhead.

void rngMoveAhead(RING_ID ringId, int n); //move inbuffer ahead n # of bytes (used after a PutAhead)

For the 32 bit version, please note that function names and data type names are the same except prefixed with either 'rng32' for functions and 'RING32' for data types. They function in an identical manner except for using unsigned long int (u32) instead of char (u8) for data.

Macros

// RNG_ELEM_PUT - put one character into a ring buffer
 
//(register int) 't'.
// c is a char
 
// returns 1 if success 0 if not
#define RNG_ELEM_PUT(r, c, t)

// RNG_ELEM_GET - get one character from a ring buffer
// p should be a char *
 
// (register int) 'f'.
 
// returns 1 if success 0 if not
#define RNG_ELEM_GET(r,p,f)

Examples

Write the string into buffer and read it back out again.

char blahsrc[]="this is blah";
char blahdst[0x20];
int putcnt, getcnt;
 
//create 32 byte long rng buffer
RING_ID rid=rngCreate(0x20);
//write bytes into ring buffer
putcnt=rngBufPut(rid, blahsrc, strlen(blahsrc)+1);
//read bytes back out of ring buffer
getcnt=rngBufGet(rid, blahdst, sizeof(blahdst));
printf("put %d bytes into buffer, read %d bytes out: %s\n",putcnt,getcnt,blahdst);

ring buffers are very useful. ^^