14.3 Video processing part 1: introductory exercise  (Page 2/6)

The Chip Support Library (CSL) is an abstraction layer that allows the IDK daughterboard to be used with the entire family of TI C6000 DSPs (not just the C6711 that we're using); it takes care of what is different from chip to chip.

The Image Data Manager (IDM) is a set of routines responsible for moving data between on-chip internal memory, and external memory on the board, during processing. The IDM helps the programmer by taking care of the pointer updates and buffer management involved in transferring data. Your DSP algorithms will read and write to internal memory, and the IDM will transfer this data to and from external memory. Examples of external memory include temporary "scratch pad" buffers, the input buffer containing data from the camera, and the output buffer with data destined for the RGB output.

The two different memory units exist to provide rapid access to a larger memory capacity. The external memory is very large in size – around 16 MB, but is slow to access. But the internal is only about 25 KB or so and offers very fast access times. Thus we often store large pieces of data, such as the entire input frame, in the external memory. We then bring it in to internal memory, one small portion at a time, as needed. A portion could be a line or part of a line of the frame. We then process the data in internal memory and then repeat in reverse, by outputting the results line by line (or part of) to external memory. This is full explained in Project Lab 2, and this manipulation of memory is important in designing efficient systems.

The TI C6711 DSP uses a different instruction set than the 5400 DSP's you are familiar with in lab. The IDK environment was designed with high level programming in mind, so that programmers would be isolated from the intricacies of assembly programming. Therefore, we strongly suggest that you do all your programming in C. Programs on the IDK typically consist of a main program that calls an image processing routine.

The main program serves to setup the memory spaces needed and store the pointers to these in objects for easy access. It also sets up the input and output channels and the hardware modes (color/grayscale ...). In short it prepares the system for our image processing algorithm.

The image processing routine may make several calls to specialized functions. These specialized functions consist of an outer wrapper and an inner component. The wrapper oversees the processing of the entire image, while the component function works on parts of an image at a time. And the IDM moves data back and forth between internal and external memory.

As it brings in one line in from external memory, the component function performs the processing on this one line. Results are sent back to the wrapper. And finally the wrapper contains the IDM instructions to pass the output to external memory or wherever else it may be needed.

Please note that this is a good methodology used in programming for the IDK. However it is very flexible too, the "wrapper" and "component functions" are C functions and return values, take in parameters and so on too. And it is possible to extract/output multiple lines or block etc. as later shown.