Cirque is in a very competitive, high volume consumer electronics market space. We have been shipping computer touchpad controller chips since 1991.
We recently wanted to update one of our touch controller chips to enhance several analog and digital features and to reduce the cost. Three months before we planned on finalizing the digital design, we learned of an open source, royalty free 32-bit RISC CPU core called RISC-V. Our current CPU core choice worked fine, but the toolchain was unsupported, and the royalties were too high for our market space. This new CPU core option looked very attractive, but it wasn’t quite a drop-in replacement for the current core. This RISC-V core also didn’t have some of the peripherals needed, including timers and UART. Changing the CPU core in an ASIC is typically a big commitment and has a considerable impact on system performance, including firmware code development. We decided to spend 2 weeks shopping for other CPU core options that might be a better fit for our application.
We quickly found a wide range of eSi-RISC CPU cores on EnSilica’s website. These cores had very competitive specs and came with all the other peripherals we needed. Their website was easy to navigate and contained all of the information we needed without requiring an NDA to access it.
We considered other CPU vendors, but we found that their websites did not provide adequate information. To obtain information from these vendors we were required to secure NDAs and multiple email communications. This led to significant delays in gathering the needed comparative data for us to make a decision.
This chip revision had a very aggressive design cycle. Because of this, one of our primary requirements for replacing the CPU core was that it needed to be a near drop-in replacement. The current CPU core and in-house peripherals used a non-standard peripheral bus which was not available with the eSi-RISC core. After describing this issue and the peripheral bus function to the EnSilica engineering team, they were able to generate a peripheral bus conversion module and delivered a full RTL package for us to evaluate in one day, including the peripherals that we needed and all of the customized parameters that were required for our design. EnSilica did not require additional NDA agreements to get the evaluation, which saved precious time.
Some of the EnSilica cores have optional cache memories. This was very intriguing, but we weren’t sure how much added performance it would provide our design. EnSilica suggested we try it out and we could easily remove the option if it wasn’t needed. They provided the cache option in the evaluation RTL so that we could run simulations and synthesis to see if it was a good fit for us. In the end, we decided not to use the cache, but we were impressed by how quickly they responded to changing parameters.
During the integration and verification, we had a number of questions and debug issues that came up. We were very pleased with the responsiveness of the EnSilica support team. Whenever we emailed questions, no matter the time of day, we almost always got an immediate response and most of the time with a concise and complete answer.
We planned on having 2 of our engineers do the integration and verification, but one was predisposed on another project for almost the entire 2 months. The EnSilica RTL was easy enough to read and to debug that, along with the help of one of their support engineer, we met our digital completion schedule with only one engineer on a tight deadline.
The eSi-RISC core was very attractive for many reasons:
· No royalty payments
· Low instance cost
· Flexible architecture made it a near drop-in replacement of our previous CPU core
· Impressive performance specs
· Low gate count
· Came with the peripherals we needed
· Excellent upfront sales documentation that answered all the competitive and integration questions
· Very good implementation guides and user guides
· Excellent technical support based in the UK
· Easy to read RTL
· Test bench modules that make debugging easy
We have been very happy with all aspects of the eSi-RISC cores and we highly recommend them