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elixir-circuits / circuits_uart

Discover and use UARTs and serial ports in Elixir
Apache License 2.0
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Latency #70

Open robinhilliard opened 5 years ago

robinhilliard commented 5 years ago

Setup

Expected Behavior

No significant latency

Actual Behavior

Latency up to a second with modems set to 20ms window to minimise buffering

Steps to Reproduce the Problem

I have a pair of radio modems at close to point blank range set to 57600 baud sending a short < 100 byte message. The modems have a firmware maximum window size config of 20ms which is the setting normally used to minimise latency. I minimised the number of other messages (they support sending hundreds of messages of similar size with no throughput issues), and the same software setup running over WiFi/UDP has no noticable delay. However when I use the modems with one of them via circuits UART I get a latency delay of about a second. I have set the uart connection to active.

I know there are lots of variables in play here, but I was wondering if there are any configuration settings you would use to minimise latency of short messages when using this library?

Thanks, Robin

fhunleth commented 5 years ago

My use of Circuits UART isn't performance critical and I know that Circuits.UART performance could be improved. However, I wasn't expecting issues on an MBP at 57600.

Just so I understand right, the firmware at the other end times out since it doesn't receive a message in 20 ms. At 57600 baud, a 100 byte message takes about 17 ms to send. If it's delayed by 3 ms, then it times out?

robinhilliard commented 5 years ago

Hi Frank,

Sorry the window size just means that it sends what it has in it’s buffers every 20ms. I can see the timeout arguments in the C code and mention of polling but don’t understand what it’s doing, and wondered if perhaps there was a polling interval or other setting in there that could be tweaked.

Cheers Robin

fhunleth commented 5 years ago

Does the firmware work with any other software on your Mac? For example, does it work with Picocom? It's sounding like it's not a Circuits.UART issue, but a general issue that writing bytes to the serial port doesn't work well.

Is the C code that you're referring to posted anywhere?