Dear cheezor,

reviewing your code was not that easy. I can ee the timer checking the accumulator content for zero but not the influence on the audio signal. Anyways there are two other possibilities to mute the signal by flipping a bit:

1.) Flip the sign bit, this is corresponding the guard bits in accumulator a2 correspinding to bit 23 in the operand registers. Be careful not to change bit 47 in the accumulator since this is _not_ the sign bit - this is inherent in the accumulator guard bits.

The result is the same as moving -1.0 to any of those registers. Afterwards the polarity should be inverted in the accumulator by the 'neg a' instruction. Note that writing ~1.0 = 0.9999998 to a register is done by flipping _all_ bits except the sign bit, but maybe the right polarity of the output signal isn't an issue for your application.

2.) Use the flipped bit to control writing 0.9999998 or 0.0000000 corresponding to 1.0 and 0.0 correspondingly. This is really annoying but the DSP can handle control istructions much worse than a microcontroller. Code branches are relatively unusual in DSP algorithms compared to the tight MAC loops this architecture was designed for. It is possible to code conditional code execution but this is more nasty than on ARM or even 8051. We can have conditional code execution but only for BRxx and Jxx (or BRSxx and JSxx for subroutines) where xx is corersponding to the status register flag settings combinations.

In each case have a try with the Symphony Studio simulator for first. Small items like this can be observed conveniently by changing the register numbering formats from fractional, interger and hexadecimal on the fly.

Have fun checking the DSP563xx architecture with the simulator,

Christian