Added ensogen description

Author: kaajalbgupta

README.md

@@ -61,3 +61,15 @@ sudo -i
 ```
 
 Then, must load the machine with that bitstream: `enso enso/ --host mxhost --fpga 1-12`. The correct sha256 for this bitstream is `2f12a0862f51c2ca5c293216bfe46de60db7f27523ef3ee9114286d0ecbab2b7`.
+
+An example command incorporating some new features is:
+```
+sudo enso/build/software/examples/ensogen enso/frontend/pcaps/64_1_100_0_1200000_100000.pcap 1 175 --core 0  --queues 4 --save stats.csv --pcie-addr 0000:65:00.0 --rtt-hist hist --distribution constant --poisson
+```
+The distribution option specifies the distribution of the number of cycles to spin for per packet provided to the receiving thread. This information is kept at the start of each packet (at offset 0). The distribution can be either constant, exponential, or bimodal. The constant option is simply 10 us per packet. The exponential option is the exponential distribution with a mean of 10 us. The bimodal option is 55 us 10% of the time, and 5 us the rest of the time.
+
+When the poisson option is enabled, per-packet rate limiting occurs instead of per-device. When per-packet rate limiting is enabled, the NIC uses the delay in each packet (which is present at the offset kPacketRttOffset) to decide when to send the packet. We can generate PCAP files that have packets with the correct delays for a certain intended packet rate with `./hardware/input_gen/generate_synthetic_trace`. An example usage of it that creates the PCAP above (64_1_100_0_1200000_100000):
+```
+build/hardware/input_gen/generate_synthetic_trace 64 1 100 0 --output-pcap frontend/pcaps/64_1_100_0_1200000_100000.pcap --request-rate 1200000 --request-rate 100000
+```
+This creates a PCAP file with packet size 64 bytes, with one source IP, a hundred destination IPs, and has two request rates (that will alternate between each other in 1 second intervals): 1200 kpps and 100 kpps. To create a PCAP that only has a single request rate, only one request rate need be specified.