SRL_STYLE instructs the synthesis tool
on how to infer SRLs found in the design. Accepted values are:
- register
- The tool does not infer an SRL but instead only uses registers.
- srl
- The tool infers an SRL without any registers before or after.
- srl_reg
- The tool infers an SRL and leaves one register after the SRL.
- reg_srl
- The tool infers an SRL and leaves one register before the SRL.
- reg_srl_reg
- The tool infers an SRL and leaves one register before and one after the SRL.
- block
- The tool infers the SRL inside a block RAM.
Place SRL_STYLE on the signal
declared for SRL. This attribute can be set in RTL and XDC. The attribute can only be
used on static SRLs. The indexing logic for dynamic SRLs is located within the SRL
component itself. Therefore, the logic cannot be created around the SRL component to
look up addresses outside of the component.
Note: Use care when using combinations of
SRL_STYLE, SHREG_EXTRACT,
and -shreg_min_size. The SHREG_EXTRACT attribute always takes precedence over the others. If
SHREG_EXTRACT is set to "no" and SRL_STYLE is set to "srl", registers are used. The -shreg_min_size, being the global variable, always has the least amount of
precedence. If an SRL of length 10 is set and SRL_STYLE
is set to "srl", and -shreg_min_size is set to 20, the SRL is still inferred.Note: In the following examples, the SRLs are all created
with buses where the SRL shifts from one bit to the next. If the code to use
SRL_STYLE has many differently named signals driving each
other, place the SRL_STYLE attribute on the last signal
in the chain. This includes if the last register in the chain is in a different
hierarchy level than the other registers. The attribute always goes on the last register
in the chain.