Fixed-point LIF ProcModel not bit-accurate to Loihi after spike

[mathisrichter]

Objective of issue: The "bit-accurate" ProcessModel of the LIF Process is not actually bit-accurate with respect to the hardware implementation on Loihi. After a spike, the voltage is reset to 0, whereas on the hardware it is reset to 128.

Lava version:

• [x] 0.4.0 (current version)

I'm submitting a ...

• [x] bug report
• [ ] feature request
• [ ] documentation request

Current behavior:

• Voltage is reset to 0 after spike.

Expected behavior:

• Voltage is reset to 128 after spike.

Steps to reproduce:

Related code:

insert short code snippets here

Other information:

insert the output from lava debug here

[JuliaA369]

I believe that this is just a reporting difference. The internal (hidden) states should be the same. You can confirm this by looking at when subsequent spikes occur.

[mathisrichter]

The state of the voltage on Loihi is in fact 128 after a spike. As you are correctly pointing out, that initial voltage does not have an impact on its later evolution.

I think this behavior should still be reflected in the Python ProcessModel to enable easy comparison between results from hardware and simulation.