Basics of core-based FPGA design: Part 1 – core types & trade-offs

R.C. Cofer and Ben Harding

August 17, 2011

R.C. Cofer and Ben Harding

The following lists present a generalized summary of the advantages and disadvantages for each of the FPGA processor core types (soft, firm and hard).

Soft Core Advantages and Disadvantages

Advantages
- Generally a much higher level of portability
– Generally most affordable
– More low-cost/free sources due to easier implementation
– Relatively easy to target to specific architectures
– Relatively easy to modify
Disadvantages
– Possibility of portability between architectures
– Much lower level of optimization resulting in: lower performance levels, higher resource utilization
– May require more design effort
– Likely less extensive simulation results for specific architectures
– Likely less documentation for specific architectures
– Differences in tool sets used for design implementation can affect results significantly and are not always predictable

Firm Core Advantages and Disadvantages

Advantages
– Likely well-optimized for targeted architecture
– Relatively easy to modify
– Performance, resource utilization and power consumption information generally well-characterized
– Generally provide a high level of confidence in functionality / performance
– Design already fielded and verified
– Easy to test in target environment
– Access to some level of simulation resources (testbenches and results)
– Some level of documentation available
– Potential access to design expertise
Disadvantages
– There are limited incentives for manufacturer-developed firm cores to be highly portable
– Level of documentation, design configurability, simulation support and access to original design team may be variable
– Access to advance design assistance from IP source may be fee-for-service depending on the negotiated terms

Hard Core Advantages and Disadvantages
Advantages
– Well documented, highly-optimized, high-performance, reliable fixed implementation
– Similar to purchase of a standard IC component
– No delay, immediate access to functionality
– High level of confidence in functionality, known errata
– Measured and well-characterized
– Functionality
– Performance
– Power consumption
Disadvantages
– Generally so highly-optimized and fine tuned, difficult to port to other targets with equivalent performance or at an affordable price point
– Strong incentive for provider to try to strongly tie to their architecture and make it less attractive to port to alternative architectures
– Fixed implementation, unable to modify core implementation or add additional instances if required without switching devices within the family