Implementation Before implementing the entire system shown in Multirate Processing: Introduction, we recommend you design a system that consists of a cascade of filters FIR 1 and FIR 2 without the sample-rate compressor or expander. After verifying that the response of your two-filter system is correct, proceed to implement the complete multirate system and verify its total response. At first, use fixed compression and expansion factors of D U 4 . After you have verified that the multirate system works at a fixed rate, you should modify your code so that the rate can be changed easily. You must be able to quickly change the compression and expansion factors when you demo your code.

Compressed-rate processing In order to perform the processing at the lower sample rate, implement a counter in your code. Your counter will determine when the compressed-rate processing is to occur, and it can also be used to determine when to insert zeros into FIR 3 to implement the sample-rate expander. Some instructions that may be useful for implementing your multirate structure are the add and bcc (branch conditional) instructions. You may also find the b (branch) instruction useful. The conditional fields that can be used with bcc can be found on page 1-7 of the 55x Mnemonic Instruction Set.