Max baud rate for OpenLog vs. OpenLog Artemis

Other Miscellaneous
1

I’d like to use OpenLog to write serial data at relatively high speed (at least 384 kbps, ideally 512 kbps).

I am finding conflicting information on which of the two OpenLog boards (atmega vs. artemis) could handle this:

  • according to the main OpenLog product page, it’s only up to 115200 bps: https://www.sparkfun.com/products/13712

  • but the tutorial for that product (along with anectodal reports from various forums) suggest up to 1Mbps:

https://learn.sparkfun.com/tutorials/op … okup-guide (System Settings)

Which one can I trust, do you think the atmega OpenLog could work at these speeds?

2

The ATmega OpenLog definitely will not work at those speeds, the Artemis OpenLog might be OK above 500K as long as your data isn’t a continuous stream or contains large amounts of data. The Artemis OpenLog needs a bit of a break every now and then so it can do housekeeping chores like writing to the SD card and such.

3

Thanks, that’s good to know! The requirements I quoted are for sustained writes, so no, there is no pause in the datastream and I’d like these speeds to be stable for hours / days.

I wonder how much potential there is to further improve the OpenLog Artemis firmware eg. by using interrupts to write input data into a large buffer and letting the main thread flush it to the card at its own pace?

I could achieve these speeds on a Teensy 4 by pre-allocating a contiguous file and using a large ring buffer of sector-sized chunks. These two optimisations reduced the latency spikes of SD writes by a lot, but the pre-allocation is a bit of a pain and there is some residual variability in write latency which makes life harder for the rest of the program. Hence the idea to delegate SD card handling to OpenLog.