Variable clock frequency

[bo3z]

Currently the clock frequency is only partially modifiable. By partially I mean that it can be specified in the Makefile when linking the designing, which directly affects PnR. However, the frequency is hard-coded for most kernels (e.g. vadd_put) in the .tcl script.

While this has no impact on PnR, it can affect HLS synthesis - The HLS compiler uses the clock frequency to schedule the design, and, with a higher frequency the design can take more clock cycles. So if performing HLS compilation with e.g. 250 MHz but PnR with 200 MHz, there can be a performance drop due to added clock cycles.

I will try to open a PR for this, so that the operating frequency can be set for each part of ACCL and is propagated from the top-level Makefile.