9.1.1. ALU Folding Limitations
For designs that use more than one data type, a Convert block between two data types uses more resources if the design requires saturation and rounding. An unbiased rounding operation uses more resources than a biased rounding mode.
Some DSP Builder blocks store state, for example:
- Sample Delay
With ALU folding, any blocks that store state have a separate state for each channel. DSP Builder only updates the state for a channel when the system processes the channel. Thus, a sample delay delays a signal until processing the next data sample. For 200 clock cycles to a data period, DSP Builder delays the signal for the 200 clock cycles. Also, data associated with one channel cannot affect the state associated with any other channel. Changing the number of channels does not affect the behavior of the design.