NEC engineers advance hardware/software co-verification

"Such combined systems already exist, but the strong point of our system is that every step of a program's execution completely synchronizes between the simulator and the emulator," said Yuichi Nakamura, principal researcher of multimedia architecture technology group at NEC's Media and Information Research laboratories.

"It's important that the verification system behave the same way as the actual device does," said Nakamura. He noted that RTL simulators are expensive but slow, while commercial FPGA-based emulation systems can cost millions of dollars.

If a program runs in one second on an actual device with 100 MHz clock, it takes about 2 minutes for the same program to run on an FPGA emulator operating at 1 MHz, and it takes about 100 days on a RTL simulator operating at 10 kHz. C/C++ simulators are between RTL simulators and FPGA emulators in terms of speed but are inferior in accuracy, according to NEC.

NEC engineers combined a PC-based C/C++ simulator that works at about 100 kHz with a small-scale FPGA emulator that costs a few tens of thousands of dollars. NEC engineers say the combined system is as accurate as RTL simulation but is about 1,000 times faster.

The PC simulator and the FPGA are connected by shared communication registers, which correspond to a bus in actual device. The register array is implemented on the FPGA emulator. The registers make it possible to send an instruction from the PC simulator and to receive a response to the instruction from the FPGA emulator in the same system cycle.

Lines of code can be executed one at a time, with the emulator returning a value at every step. "At whatever point a bug occurs, we can stop the execution on the spot and check the cause," said Nakamura.

NEC has been developing the verification system since 2000. The system was used to develop NEC Electronics' LSIs for DVD recorders. "The embedded software developed prior to the device fabrication run on the devices at once without any bugs," said Nakamura. The verification system lets designers develop embedded software in parallel with hardware design, without waiting for the actual device being fabricated and becoming available, he said.

NEC Electronics intends to introduce about 50 of these verification systems internally by autumn this year. NEC also intends to make it available to its customers who want to develop embedded software by themselves. "Our support resources are limited, so the system will be available only to our customers for the time being," said Nakamura.