February 1998, Issue 91

Low-Cost Voice Recognition

TINY ALGORITHMS

The software for Tiny Voice was written entirely in assembly. There is a total of eight routines.

The main program, MAIN.ASM, responds to events and schedules the remaining subroutines.

COMPARE.SUB handles the pattern matching. It compares the input template to each active template in memory and calculates the best match.

EEPROM.SUB handles the reading and writing of data to the EEPROM. It bit-bangs two I/O pins to simulate an I2C protocol used by the EEPROM.

IRQ.SUB is the interrupt handler. Interrupts are caused by a button press.

The most complicated routine is INPUT.SUB. It samples the input, determines where the word starts and ends, and builds up the voice template.

TIME_NOR.SUB normalizes the length of the speech input to a fixed length of twelve two-element data values.

DIV16_8.SUB is an integer divide routine that divides a 16-bit number by an 8-bit number. This routine is called repeatedly by the time-normalization routine.

And finally, DELAYMS.SUB is a simple program where a delay is set by the value passed in the accumulator.

Tiny Voice is entirely event-driven and spends most of its time in the Stop mode. Events are caused by the interrupt of pressing push buttons. The event handler is shown in Figure 3.