METHODOLOGY OF TOPOLOGICAL RESTRICTIONS FOR INTENSIVELY USED FPGA RESOURCE

Abstract

In the paper we consider the problem of achieving high real performance of reconfigurable
computer systems in implementing computationally expensive tasks from various problem areas.
The parameters of the programs executed on reconfigurable systems determine their real performance.
The main component of these programs is the computing data processing structures implemented
as FPGA configuration files. At the same time, one of the key parameters of any computing
structure is the clock frequency of its operation, which directly affects its performance. However,
there are several problems concerning the achievement of high clock rates, and they cannot be solved
with the help of modern CAD tools. The reason is the non-optimal topological placement of functional
blocks of the computing structure within the field of FPGA primitives, especially with high resource
utilization. Due to this, the load on the FPGA switching matrix is increasing, and, as a result,
the connections among functionally dependent FPGA primitives turn out to be much longer than is
acceptable. In addition, excessive connection length is observed when tracing connections among
primitives that are placed on different FPGA chips or are physically separated by on-chip peripherals.
In the paper we describe a methodology which provides optimization of the placement of computing
structure elements on FPGA primitives, and minimizes the length of traces among primitives,
and also minimizes the number of traces among physically separated FPGA topological sections.
To prove the proposed methodology, we implemented the test task "FIR-filter" on a reconfigurable
computer "Tertius." We have demonstrated the main problems concerning reaching the target clock
rate and have described a method for their solution. Owing to our methodology, it is possible to
increase the clock rate; hence, the performance of Tertius will increase by 25% without revising
the functional circuit of the task’s computing structure. According to our current research of the
suggested methodology and its efficiency, we claim that CAD tools, used for creating topological
restrictions and based on our methodology, will significantly reduce the time for developing programs
with the required characteristics for reconfigurable computer systems.