OPTIMIZING CONTROL ALGORITHMS ON THE 'C5X

In many control algorithms, a value that resides in the 32-bit accumulator must either be stored to a 16-bit memory location or to a peripheral device that may be less than or equal to 16 bits in resolution, i.e., 8-bit A/D converter. Prior to storage, a range check must be performed on the sign bit (S) and the guard bits (G) in the accumulator. For positive numbers within range of the desired value, S = G = 0 and for negative numbers, S = G = 1. If this is not the case, then overflow has occurred and the value stored must be saturated. Standard published code to perform this saturation can take up to 15 cycles. This overhead can be minimized using the technique shown.

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