Adaptive FPGA Programming for SVF and STAPL/JAM

Introduction

There are two common file standards for programming FPGAs: SVF and STAPL/JAM.
Most vendors can generate either type of file, but which should you choose?
First we should look at a significant difference between the two: STAPL allows
the use of conditional expressions, while SVF does not. In terms of FPGA & CPLD
programming, this means STAPL can provide adaptive programming, while SVF is
limited to delays.

How It Affects Programming Speed

In general, an adaptive programming algorithm will run faster than a
non-adaptive programming algorithm, since it can poll the device status and
determine exactly when programming has been completed and execution may resume.
Non-adaptive programming algorithms must wait a pre-defined time—usually the
device’s worst case program time—before proceeding.

The flow charts below show simplified examples of programming algorithms:

Figure 1: Programming flow charts

If the worst case delay far exceeds the typical and minimum delay, then the
adaptive programming will finish first. In some cases, increasing the clock rate
and shortening the delay on the non-adaptive file may allow it to surpass the
adaptive programming speed.

Conclusion

STAPL files can often provide better programming performance than SVF files.
Despite the lack of adaptive programming features in SVF, ScanExpress Runner and
ScanExpress Programmer JTAG implement some techniques in SVF execution to speed
up programming, such as re-scanning on failure and adjusting delay time when a
particular suffix (_xilinx.svf, etc.) is used. Additionally, Lattice has
expanded their SVF files to include non-standard LOOP statements to facilitate
adaptive programming.

What is your experience with CPLD and FPGA programming? We’re always seeing new
and unusual cases—a new FPGA programs slower than its previous version, STAPL
executes much faster than SVF and in the odd case, SVF executes much faster than
STAPL, etc.—and look for input to help improve our software.

Source: SVF and STAPL/JAM: Adaptive FPGA Programming