Performing Multibit Register Optimization

Performing Multibit Register Optimization

. Combining (Banking) and splitting (Debanking)

-> Tool can combine (Banking) single-bit registers or smaller multibit registers

and replace them with equivalent larger multibit registers.

. Example:

-> the tool can combine eight 1-bit registers or four 2-bit register banks and replace them with one 8- bit register bank or two 4-bit register banks.

-> The tool merges single-bit registers only if, they have the same timing constraints.

->Replacing single-bit registers with multibit registers reduces

• Area due to shared transistors and optimized transistor-level layout
• • The total clock tree net length
• • The number of clock tree buffers and clock tree power

Splitting ( debanking)

-> The tool can also split (debank) large multibit registers into smaller multibit registers or single-bit registers, if it improves the total negative slack.

To perform multibit register optimization during the place_opt command

1. set_app_options -name place_opt.flow.enable_multibit_banking -value true
2. 2. Enable multibit register rewiring by setting the
3. . set_app_options -name place_opt.flow.enable_multibit_rewiring -value true
4. 3. Specify settings for multibit register banking by using the set_multibit_options command.
5. 4. place_opt
6. 5. report_multibit

-> Identify the groups of cells that can be replaced by multibit cells by using the identify_multibit command,

. identify_multibit -apply -register -mv_cell

-> If multibit banking does not improve QoR, split specific multibit banks into individual registers or smaller multibit banks by using the split_multibit command.

. split_multibit reg_gr0 -lib_cells {lib1/MREG2 lib1/MREG2}

analysis report_multibit

a) single-bit flip flop

b) single-bit latches

c) Multi-bit flip flop

d) Multi-bit latches

**** Sequential cell banking ratio = (c + d) / (a + b + c + d)

**** Flip flop cell banking ratio = (c) / (a + c)