Questions about latency using the logic analyzer and logic 2 software

Hi, I’m new to the community, but have found the logic 2 software very helpful in debugging my Async serial communications. I’m now moving onto automating my system and was considering using the logic analyzer to record data, but I was curios about a few things.

  1. Can anyone provide information on the delay of a logic analyzer from the moment it receives a signal to it being received by the computer? Is this in the nanoseconds range or are there some buffers that store data and send it to the computer at slightly slower rate?
  2. Could you be able to provide information on how long it takes the code to the async serial data? I noticed on the gui that sometimes there is a few seconds to minutes wait between when I finish collecting data to when the program allows me to export data because the analyzer is still processing the data I collected.
    2.Additionally I saw this post about continuously saving while the analyzer is capturing, but I was wondering if there is a more direct way to access the decoded byte that was captured and plot it immediately rather than saving it?

The answer to your questions depends a lot on your specific setup. The data is streamed from the Logic hardware over USB to your PC, where it is then buffered, processed, and displayed.

If you have a high-performance PC, then this likely happens in ‘near real-time’ (probably within tens or hundreds of milliseconds, or so). It will not be in the nanosecond range, as it will take longer to sample, buffer, transmit, and decode the data than that timeframe.

This timeline also depends on your capture settings vs. your PC performance, including:

  • sample rate settings
    (the faster the rate, the more data to transfer and process)
  • number of channels being captured
    (the more channels captured, also more data to transfer and process)
  • analog vs. digital data sampling
    (analog data captures transfer a lot more data than digital – transferring every analog sample vs. just the digital sample edges/transitions)
  • use of glitch filtering
    (glitch filtering adds more processing overhead, and can add capture latency/buffering)
  • USB port speed and USB driver
    (i.e., USB3.0 vs. USB2.0 for Logic Pro will be a bottleneck due to reduced maximum bit-rate; likewise a bad/old USB driver may not provide maximum USB performance)
  • Other devices on the same USB bus as Logic hardware
    (for maximum bandwidth, best to have only the Logic hardware on a given bus to avoid interference when other device is using the bus)
  • Other software running on the PC
    (There is still a lot of data processing on the PC side after data is received from the hardware; if other programs are using up CPU cycles, then PC may not keep up with received data)
  • The host PC performance itself
    (amount of RAM, CPU speed, etc. all impact how well PC can ‘keep up’ with received data)

If the Logic 2 software is having troubles keeping up with the data. then it will be difficult to have an alternative method that is any faster – most alternatives run on top of the base Logic 2 software, and will only require more resources then the base software package (e.g., adding a custom low-level and/or high-level analyzer on top of the base Logic 2 program).

Besides writing an HLA as described in the post above, we don’t provide any direct means of accessing data during a capture.