Config reference: L0 simulator

In this section, we document the YAML configuration file which is used by the L0 simulator.

• nbeams (integer).

  Number of beams being simulated. Must match the value of ‘nbeams’ in the L1 server’s config file.

• nfreq (integer).

  Number of frequency channels (usually 1024 in subscale testing, or 16384 in production-scale). Must match the value of ‘nfreq’ in the L1 server’s config file.

• nt_per_packet (integer).

  Number of time samples sent in each UDP packet. Must match the value of ‘nt_per_packet’ in the L1 server’s config file.

• fpga_counts_per_sample (integer, default 384).

  Number of FPGA counts per time sample. Must match the value of ‘fpga_counts_per_sample’ in the L1 server’s config file.

  This is an indirect way of specifiying the sampling rate. One FPGA count corresponds to 2.5 microseconds (hardcoded). Therefore, the default value fpga_counts_per_sample=384 corresponds to a sampling rate of 0.983 milliseconds.

  One use for this parameter is to artificially speed up or slow down test instances. For example, to run a “stress test” in which the L1 server is required to run 10% faster than normal, you can take fpga_counts_per_sample=349. (Note that you’ll also need to decrease the value of ‘dt_sample’ in the bonsai config file by 10%, and the max DM of the search will automatically decrease by 10%.)

• ipaddr (either a string, or a list of strings).

  This has the same meaning as the ipaddr parameter in the L1 config file (see above).

  It can either be a list of strings (one for each stream) or a single string (if all strings use the same IP address). IP addresses are specified as strings, e.g. "127.0.0.1".

• port (either an integer, or a list of integers).

  This has the same meaning as the port parameter in the L1 config file (see above).

  One or more UDP ports, for the L1 server’s stream(s). This can be either a list of UDP ports (one for each stream), or a single UDP port (if all streams use the same port).

• nthreads (integer).

  Number of threads used by the L0 simulator. This must be a multiple of the number of streams, i.e. the number of distinct (ipaddr, udp_port) pairs. Usually I just set nthreads = nstreams.

• max_packet_size (integer, default 8900).

  If running on a network with ethernet jumbo frames enabled, the default of 8900 bytes is a good choice. Otherwise, I suggest 1400.

• nfreq_coarse_per_packet (integer, optional).

  If specified, this determines the number of “coarse” frequency channels sent per packet. A “coarse” frequency channel is always 1/1024 of the full CHIME band. For example, if nfreq=16384, then one coarse frequency channel contains 16 “fine” frequency channels.

  If unspecified, then nfreq_coarse_per_packet will be automatically determined by the max_packet_size. (We send as many frequency channels as possible, given the max packet size constraint, the number of beams and time samples, and some internal constraints of the code.)

• initial_time_index (integer, default 0).

  Time index of the first packet sent by the simulator. (More precisely, the FPGA count in the first packet will be initial_time_index * fpga_counts_per_sample.)