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How it works
A data request is sent to the ESP hub. The response may contain either receive or transmit data, but
not both; it will also contain status. If data is available, it is read and saved in a receive or transmit
data bucket. If there is no data available, the state of the control signals will be checked. If there
was a control signal change, the sample will be saved, even if there is no data to save.
Once a successful sample is collected, the most recent status is checked to see if there is any more
data pending to be read. If there is, the next sample is requested immediately. If not, a 50
millisecond delay is invoked before the next sample. This mitigates the amount of TCP traffic
generated by the datascope when the serial port is not busy.
Sample buckets
Each sample is collected in a bucket that may contain up to 1024 characters, plus the corresponding
control signals. Buckets are stored in a circular buffer. You may configure the maximum number of
buckets in the buffer. If the maximum is exceeded, the oldest buckets are overwritten.
Data is saved only if there has been a change in state during the five second time-out interval, that
is, if data has been transmitted or received or a change in the control signals is detected.
(Theoretically, if there is no data traffic on the serial interface, buckets could be filled with only
control signals, and no data would be available for later analysis. This occurrence is unlikely,
but possible.)
The sampling rate is driven by data or time-outs, not the control signals. It is therefore possible that
multiple control signal transitions could occur and not be recorded. However, this prevents rapidly
filling all the buckets if there is a floating signal or if many flow control transitions occur.
When data is being sampled, it is requested with a five second time-out. If there is no data
movement and a sampling exchange returns due to a time-out, the state of the control signals is
checked and compared to the previous sample. If the control signals have changed, a sample bucket
will be filled with zero data and the new state of the control signals. So, even when there is no data
traffic on the serial interface, the control signals will be checked every five seconds.
To use the datascope function:
1.
Launch the ESP-View utility.
2.
Click the Datascope tab or select Tools - Datascope from the ESP-View utility menu.
3.
In the Settings panel, select a port in the ESP Port listbox.
4.
In the Size listbox, change the maximum number of sample buckets in the circular buffer.
5.
To start polling, click Start. A rotating circle will appear in the lower right corner of the win-
dow to indicate that the datascope is running.
6.
To pause polling, click Pause. To resume, click Pause again.
7.
To stop polling, click Stop.
You will be prompted to Review, Save or Cancel the session.
Chapter 8: ESP-View Diagnostic Utility
69
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