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This module describes the basics of the Queue (QUE) module in DSP/BIOS v5.x. It also shows how to use the MEM module to allocate memory for queue elements.
The QUE module provides a way to manage linked lists of data objects. A linked list is a group of objects where an object in the list has information about the previous and next elements in the list as demonstrated in Figure 1. A linked list can be used to implement buffers that operate in a FIFO, LIFO, LILO and FILO manner, to name a few. Many times it is used in a FIFO manner.
The basic element in a queue structure is a
QUE_Elem which is defined by
typedef struct QUE_Elem {
struct QUE_Elem *next;struct QUE_Elem *prev;
} QUE_Elem;
This definition is in the header file
que.h which must be included in the source file.
A message or object put on a queue is a structure that has as its first element a
QUE_Elem . The message is defined by the user's code. An example would be:
typedef struct MsgObj {
QUE_Elem elem; /* first field for QUE */Int val; /* message value */
} MsgObj, *Msg;
To put a message at the end of a queue use the function
QUE_put and to remove a message from the beginning of the queue use
QUE_get . These two functions allow the queue to be used as a First In First Out (FIFO) buffer.
Here is another example of a message structure. Notice that you can put anything else in the struture for your message as long as the QUE_Elem element is the first in the structure.
typedef struct MsgObj {
QUE_Elem elem; /* first field for QUE */float array[100]; /* message array */} MsgObj, *Msg;
When creating messages it may be necessary to get a segment of memeory to store the message. The following code can be used to allocate memory for a message and put it on a queue.
Msg msg; // pointer to a MsgObj, this doesn't allocate memory for a messagemsg = MEM_alloc(0, sizeof(MsgObj), 0); // Allocate memory for the object
if (msg == MEM_ILLEGAL) {SYS_abort("Memory allocation failed!\n");
}/* fill the message with data here */
/* This puts the address of the message in the queue */QUE_put(&queue, msg);
In order to use the MEM module the header file
mem.h must be included in the source file. The
MEM_alloc gets a segment of memory from the memory manager and returns a pointer to the segment. The address gets put into the
msg pointer so that when we access the object it points to segment of memeory.
QUE_put puts the address of the message object on the queue. This function only copies the message pointer in order to minimize the amount of processing needed to put the message on the queue.
Before trying to get a message from a queue, the code should check to see if there is a message available on the queue. The following code makes this check and then gets the message from the queue.
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