Placer using incorrect cost model on many projections

[Christian-B]

found with:
import pyNN.spiNNaker as sim

n_neurons = 10000
simtime = 1000

sim.setup(timestep=1.0, min_delay=1.0)

spikeArray = {'spike_times': [[0]]}
stimulus = sim.Population(1, sim.SpikeSourceArray, spikeArray,
label='stimulus')
pop = sim.Population(n_neurons, sim.IF_curr_exp, {}, label='chain')
pop.record("spikes")
sim.Projection(stimulus, pop,
sim.OneToOneConnector(),
sim.StaticSynapse(weight=5, delay=1))
sim.Projection(pop[n_neurons - 1], pop[0], sim.OneToOneConnector(),
sim.StaticSynapse(weight=5, delay=1))
for i in range(1000):
sim.Projection(pop[i], pop[i+1], sim.OneToOneConnector(),
sim.StaticSynapse(weight=5, delay=1))

sim.run(simtime)
neo = pop.get_data(variables=["spikes"])
spikes = neo.segments[0].spiketrains
print(spikes)
sim.end()

---

File "/home/brenninc/spinnaker/PACMAN/pacman/operations/placer_algorithms/application_placer.py", line 541, in _check_could_fit
raise PacmanTooBigToPlace(message)
pacman.exceptions.PacmanTooBigToPlace: chain will not fit on any possible Chip as a smae_chip_group requires 168184712 bytes but a Chip only has 123469792 bytes Lowering max_core_per_chip may resolve this.

[Christian-B]

May be the same bug causing #1468

[Christian-B]

The cost models are correct.
Ok maybe too high but too high is better than too low.

The example with 10,000 connectors needs 10,000 synapse table which are estimated at 168,148,712 bytes