Altera FIR Compiler II MegaCore Function - Manual (Page 33)

example, the threshold that determines whether to use M9K blocks rather than MLAB blocks on
Stratix IV devices.
1. Set the default threshold value, to implement dual memories greater than 1,280 bits as M9K blocks and
dual memories less than or equal to 1,280 bits as MLABs.
2. Change this threshold to a lower value such as 200, to implement dual memories greater than 200 bits
as M9K blocks and dual memories less than or equal to 200 bits as MLAB blocks.
Note: For device families with only one type of memory block, this threshold has no effect.
Using M-RAM Threshold
This threshold is the trade-off between medium and large RAM blocks. For larger delays, implement
memory in medium-block RAM (M4K, M9K) or use larger M-RAM blocks (M512K, M144K).
1. Set the number of bits in a memory or delay greater than this threshold, to use M-RAM.
2. Set a large value such as the default of 1,000,000 bits, to never uses M-RAM blocks.
Using Hard Multiplier Threshold
This threshold is the trade-off between hard and soft multipliers. For devices that support hard multipliers
or DSP blocks, use these resources instead of a soft multiplier made from LEs. For example, a 2-bit × 10-
bit multiplier consumes very few LEs. The hard multiplier threshold value corresponds to the number of
LEs that save a multiplier. If the hard multiplier threshold value is 100, you are allowing 100 LEs.
Therefore, an 18 × 18 multiplier (that requires approximately 182–350 LEs) is not transferred to LEs
because it requires more LEs than the threshold value. However, the IP core implements a 16 × 4
multiplier that requires approximately 64 LEs as a soft multiplier with this setting.
1. Set the default to always use hard multipliers. With this value, IP core implements a 24 × 18 multiplier
as two 18 × 18 multipliers.
2. Set a value of approximately 300 to keep 18 × 18 multipliers hard, but transform smaller multipliers to
LEs. The IP core implements a 24 × 18 multiplier as a 6 × 18 multiplier and an 18 × 18 multiplier, so
this setting builds the hybrid multipliers that you require.
3. Set a value of approximately 1,000 to implement the multipliers entirely as LEs. Essentially you are
allowing a high number (1000) of LEs to save using an 18 × 18 multiplier.
4. Set a value of approximately 10 to implement a 24 × 16 multiplier as a 36 × 36 multiplier. With the
value, you are not even allowing the adder to combine two multipliers. Therefore, the system has to
burn a 36 × 36 multiplier in a single DSP block.
3-8 Using M-RAM Threshold
UG-01072
2014.12.15
Altera Corporation FIR II IP Core Parameters
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