Specifications

SNAP has to wait for the radio to power up.
Maximum rate a SNAPpy script can toggle a GPIO pin:
1.9 kHz
Keep in mind that as a general rule, SNAPpy scripts should not be looping, the 1.9 kHz rate is only
attainable if the node is doing nothing else (for example, no radio or serial port communication).
Maximum rate for readAdc() calls:
maximum 5000 samples/second
NOTE! – This measurement was taken using a script that did not actually do anything with the data.
You will also have to take into consideration any numeric processing required (data thresholding, etc.),
as well as the need to actually store the data someplace.
Propagation Delay Tests
We used a pair of scripts such that one node would monitor an input pin, and when that pin changed
state the node would make an RPC call to a second node. The second node (upon receiving the RPC
call) would then drive one of its output pins to the same state as the first node’s input pin.
Unicast Propagation Delay: Due to the collision avoidance mechanism used by SNAP, the average
propagation delay is 5 milliseconds.
Multicast Propagation Delay: With a TTL = 1, the pin-to-pin propagation delay was measured at 4
milliseconds. With a TTL > 1, the RPC message incurs a >20 millisecond delay for each hop, plus
local retransmit delay.
I
2
C Byte Transfer Time
The actual I
2
C transfers are done using “bit banging” in software. This was measured using a logic
analyzer at 264 µs per byte.
SPI Byte Transfer Time
The actual SPI transfers are done using “bit banging” in software. This was measured using a logic
analyzer at 140 µs per byte.
Virtual Machine Performance
Instructions Per Second (IPS): 11400
Page 126 of 202 SNAP Reference Manual Document Number 600-0007K