Page 406 - Programming Microcontrollers in C

Summary 391

board. Loading the code into this board requires the use of another
development board, an HC12 FLASH PROGRAMMER. This board
contains an M68EVB912B32 board also. The code is downloaded
into the programmer board and from there it is transferred to the
FLASH memory on the second evaluation board. This combination
worked to program the FLASH, and it must be noted that the final
program worked as designed after one error was corrected.

Summary

In writing this chapter, I have attempted to show that modular
development of a program can yield very satisfying results. The program
here was reduced to several relatively small functions that could each
be developed and tested separately. Then these functions were integrated
one-by-one to build the whole program. This is not to say that this
approach is less work. Several of the modules listed above are very
complicated and require careful design to make certain that they work
as desired. Some of these modules require almost invention. For
example, the means used to express the Huffman table in the decode
routine needed several different starts before a satisfactory one was
found. Recall that the complete binary tree needed to express a Huffman
code requires 2n–1 nodes where n is the number of items being encoded.
I felt that it was desirable to express this tree by an array with no more
than 2n–1 members. The array shown in Listing 7-7 contains exactly
2n–1 bytes. It took six different tries to arrive at this particular
representation, and hence the code to decode the data.
The reward was that the final code worked in the embedded
product with almost no error.