stdp runs out of dtcm

[Christian-B]

Script:
https://github.com/SpiNNakerManchester/IntroLab/stdp.py
With n_neurons = 207

in_spikes_initialize_spike_buffer(incoming_spike_buffer_size) return False

Which looks like the dtcm cals are incorrect!

[Christian-B]

if you increase n_neurons for example to 255 you get:
[ERROR] (post_events.h: 47): Unable to allocate global STDP structures - Out of DTCM: Try reducing the number of neurons per core to fix this problem

[Christian-B]

I noticed that in https://github.com/SpiNNakerManchester/sPyNNaker/blob/master/neural_modelling/src/neuron/plasticity/stdp/post_events.h
post_event_history_t post_event_history =
(post_event_history_t) spin1_malloc(
n_neurons * sizeof(post_event_history_t));

sizeof(post_event_history_t) = 100

[Christian-B]

Is see that sizeof(post_event_history_t) will be
4 + 16 * 4 + 16 * (0 2 or 4) in this case 2

4 from uint32_t count_minus_one
16 * 4 from uint32_t times[MAX_POST_SYNAPTIC_EVENTS]
16 * (0 2 or 4) from post_trace_t traces[MAX_POST_SYNAPTIC_EVENTS];

[Christian-B]

log_info("post_trace_t %u", sizeof(post_trace_t));
gives:
[INFO] (post_events.h: 40): post_trace_t 2

Yet:
sPyNNaker/neural_modelling/makefiles/neuron/IF_curr_exp_stdp_mad_pair_additive/Makefile
has:
TIMING_DEPENDENCE = $(NEURON_DIR)/neuron/plasticity/stdp/timing_dependence/timing_nearest_pair_impl.c
which has:
typedef struct post_trace_t {
} post_trace_t;

That confuses me.

[rowleya]

sPyNNaker/neural_modelling/makefiles/neuron/IF_curr_exp_stdp_mad_pair_additive/Makefile
has:
TIMING_DEPENDENCE = $(NEURON_DIR)/neuron/plasticity/stdp/timing_dependence/timing_pair_impl.c

sPyNNaker/neural_modelling/makefiles/neuron/IF_curr_exp_stdp_mad_nearest_pair_additive/Makefile
has:
TIMING_DEPENDENCE = $(NEURON_DIR)/neuron/plasticity/stdp/timing_dependence/timing_nearest_pair_impl.c

These are two independent things. It looks like you were looking at timing_pair in this case, which as a uint16_t as post_trace_t, which is indeed 2 bytes. Thus the post_history_t structure is ~25Kb with 255 neurons on the core. This is unfortunate but not unexpected. The DTCM calculations in Python should take this into account and then the partitioner would reduce the neuron count, which would have a significant effect in this case!

[Christian-B]

reimplented get_max_atoms_per_core SpiNNakerManchester/PACMAN#206
does NOT fix this.

[andrewgait]

So as far as I can see, the partitioner only takes into account DTCM usage related to the neuron model components and the neuron recorder. There seems to have been a plan to do this for the synapse manager (and by extension for STDP I guess) but it hasn't happened yet (there's a TODO at

sPyNNaker/spynnaker/pyNN/models/neuron/synaptic_manager.py

Line 201 in 270a7b6

def get_dtcm_usage_in_bytes(self):

). Is this something we want to look at ahead of the release or is it something we should leave for the future?

[alan-stokes]

future. we could also add a master student to do this...... or a summer student