Echelon I/O Model Reference for Smart Transceivers and Neuron Chips User Manual

Page 24

Introduction

end-of-loop
processing
begins

TIME

IO_0

when

clause

(Not to scale)

IO_out call

sol

when

clause

when

clause

Figure 5. Scheduler Overhead Latency: when Clause to when Clause

The when-clause to when

clause latency, t

, in this case includes the execution

time of one io_out() function (which for a Series 3100 device with a 10 MHz input
clock, has approximately 65 μs latency; for a Series 5000 device with an 80 MHz

system clock, this latency is approximately 4 μs) and applies to an event that
always evaluates to TRUE. The actual t

for a particular application depends

on the actual task within the when statement as well as the when event that is

evaluated.

The above example not only measures the best-case minimum latency between

consecutive when clauses (whose events evaluate to TRUE), but also reveals the

scheduler’s end-of-loop overhead latency, t

sol

. As shown in Figure 5, t

is the off-

time period of the output waveform, and t

sol

is the on-time of the output

waveform, minus t

. The scheduler overhead latency, or the scheduler end-of-

loop latency, occurs just before the execution of the last when

clause in the

program.
The latency associated with the return from the io_out() function is small,

relative to that of the execution of the function call itself.

Note: Some I/O models suspend application processing until the task is complete

because they are firmware-driven. These I/O models include: bitshift,
Neurowire, parallel, software serial I/O models, I

C, magcard, magtrack, Touch

I/O, and Wiegand. However, they do not suspend network communication (which

is handled by the network processor and the media access processor).

Firmware and Hardware-Related I/O Timing
Information

All I/O updates in a Neuron Chip or Smart Transceiver are performed by the

Neuron firmware using system image function calls.