1. ECE-C662 Introduction to Behavioral Synthesis Knapp Text Ch
ECE-C662 Introduction to Behavioral Synthesis Knapp Text Ch. 1-2 Prawat Nagvajara
Design flow
Simulation and verification
RTL and behavioral design
Behavioral compiler
Representation
Allocation
Netlisting
Control FSM
Compiler outputs

2. Design flow Control Dataflow synthesis synthesis Behavioral synthesis
RTL synthesis
Logic synthesis

3. Domain-Specific Synthesis
Dataflow oriented synthesis
Input data are streams of samples
Operations on data are stream oriented
Signal flow diagrams, e.g., x = axz-1 + bu or x[k] = ax[k-1] + bu[k]
Signal processing applications, e.g., filtering, modulations, etc.
Languages and schematic capture editors available
Outputs are HDL description to behavioral or RTL synthesis tool

4. Control flow oriented synthesis
Finite state machines
States and their transitions
Input data are conditions
Hierarchical descriptions
Languages and schematic capture editors available
Outputs are HDL description to behavioral or RTL synthesis tool

5. Behavioral Synthesis
Back end for control flow and dataflow synthesis with HDL interchange format
Language-based general purpose tool
Languages: Verilog, VHDL, C, APL, ISP
Scheduling is the core activity
Create states and assign operations to states
Allocation
Operations assign to hardware and data to storage elements
Trade off latency for area and register area for combinational and interconnect area
Optimized design advantages over RTL synthesis

6. RTL Synthesis Logic synthesis
State graph; states and transitions are tightly bound to resources
Serve as a back end for other synthesis (but it can be a front-end tool in its own right)
Cumbersome, verbose and error prone
Logic synthesis
Propagation delay and area optimization
Back end for higher abstraction

7. Simulation and Verification
Simulation tests the response for particular inputs
Formal verification mathematically proves equivalence between the design and a ‘golden’ model described by math properties
E.g., a design is deadlock free, against Boolean expressions and specific functions
Design verification checks properties
Implementation verification checks, e.g., an optimized version against un-optimized version
They work well with combinational logic but the problem is very difficult for design with states, e.g., under process statements

8. RTL and Behavioral Design
Behavioral synthesis tools glue the domain-specific and RTL synthesis tools, e.g., C description to the dataflow oriented tool x=0; while (!reset) { u = read(input); x = a*x + b*u; write(output); }
Initial questions on data widths, operation ordering, rounding methods, timing, states and queue sizes are abstracts in terms of C or C++
This abstract model is translated to HDL model where interfaces and timing between modules are corrected using simulation

9. RTL and Behavioral Design continued
Synthesizable description
Processes are synthesized into separate FSMs or logic blocks. They may be connected by logic blocks.
The number of states in behavioral synthesis can be optimized and operations assigned to states can also changes post optimization
In RTL synthesis, the design decide on the FSM design

10. Schedule example: x[k] = ax[k-1] + bu[k]* := b u * + x
<=
Schedule example: x[k] = ax[k-1] + bu[k]

11. Allocation: x[k] = ax[k-1] + bu[k]
mux * u b * R * + + x
Allocation: x[k] = ax[k-1] + bu[k]

12. Behavioral Compiler Flow
HDL input: simulate
1. HDL analysis (parsing and semantic analysis) and elaboration for scheduling
2. User constraints
Timing model of the dataflow portion
Explicit user constraints, e.g., number of clock cycles
Dataflow -> gate-level netlist -> target technology
Early timing analysis (technology-specific scheduling)
3. Schedule
Assignment of operations to states

13. Behavioral Compiler Flow Continued
4. Allocate
Modules and registers are constructed
Mapping from the logical operations and data to netlist modules and registers
Outputs a logical description of the datapath-abstract resources and data transfer
5. Build netlist and control FSM
Simulation
6. Logic-level optimization; constraints and report
Timing-accurate timing simulation, testability assertion, test generation and layout
EDIF or others output