Hardware/Software Partitioning Witawas Srisa-an Embedded Systems Design and Implementation

Why so many of you could not get significant performance gains through the Stretch Processors?

Hardware/software Partitioning Decide which functions to be done in the software and which in the hardware –Cost versus performance Hardware--more cost and risk Software—more development time examples –The ol’386/387 –Graphic accelerator –Ideally, delay the decision until solutions are known But this may not be possible –Idling software developers –Big timing differences in development

Software Side Compile code to existing but not complete environment –Stub code can be used to simulate hardware interaction Function calls that simulate non existing hardware –Calls to memory mapped I/O registers –Also work well with evolution boards Supply by manufacturers Incremental code written in anticipation for new hardware components –Based on known hardware specification

Hardware SoC Mapping of complex algorithms into hardware is now possible –½ reduction in physical size = 4 times the amount of gates 0.35 micron to 0.18 micron Increasing wafer size Silicon compilation –VHDL or Verilog All modern processors use this approach IP from third party vendors –Fab-less vendors (Advanced RISC Machines)

Dealing with Defects Software bugs are tolerable and less costly to fix. Hardware bugs on the other hand… –Can cost hundreds of thousands in nonrecoverable cost (NRE) –Months of delay Many start-ups went down because of this reason –Non-performing hardware Repartitioning decision in the last minute

HW/SW Co-design and Co- verification Silicon compilation creates a single software database –One for describing hardware fabrication –One for controlling the hardware itself Specification Software Development Hardware Development Integrate and TestPrototype Development Time

HW/SW Co-design and Co- verification Silicon compilation creates a single software database –One for describing hardware fabrication –One for controlling the hardware itself Specification Software Development Hardware Development Integrate and Test Prototype saving

HW/SW Co-design and Co- verification Tools that bridge hardware and software –Co-design: develop hardware and controlling software together –Co-verification: verifying the correctness of hardware/software interface Instruction Set Simulator Bus functional model—translate high-level interface code to test vectors

Today’s Design Flow C/C++ code Stub code Object Code HDL Test Vector/ Simulation Si Foundry DB Integrate Codesign Phase Re-spin the ASIC Iterate Software Software Process Hardware Process

Summary The line that separates hardware and software is blurring –The design processes can be viewed as similar –The artifacts can also be viewed as similar Co-design and co-verification can reduce the development time/cost and promote better synchronization between software and hardware engineers.

Once you’ve decide … Hardware –ASIC –Stretch –What else? Software –C/C++ –Assembly –Java,.NET

Instruction Extension Many soft-core processors today allow you to create custom instruction (e.g. Altera Nios) –add your own logic block –create software macro to access the new instruction –can be combinational (single-cycle) or sequential (multi-cycle)