5 ms·

What about RS-232 and LPT?

by elcct 11y ago

lsc 11y ago
I and most people in my job role carry usb -> DB9 rs232 dongles. doesn't work, of course, if you are trying to set up a serial console to debug the laptop, which is annoying, but it works fine for what we mostly use it for, which is to say, reading other serial consoles.
pjc50 11y ago
They're obsolete for consumer hardware and take up a lot of space, while a physical gigabit network port is extremely useful for low-latency high-throughput communication, such as to NAS. (RS-232 is still somewhat useful for hobby embedded stuff, but everyone just buys FTDI clone USB-serial cables)
- monocasa 11y ago
  Unfortunately the FTDI stuff (really any USB<->UART converter) has latency issues in the embedded space. : \
  - seiferteric 11y ago
    I was wondering, would it be possible to create a better converter that did usb -> rs232/parallel port that had a special driver to put timing info? At least for driving CNC motors with a parallel port, timing is critical, you could send the pulse signal along with a timing, like 1 @ t0, 0 @ t0+1us etc.. Reading would be similar. The chip on the converter would have an accurate clock and faithfully reproduce the desired signal.
    - pjc50 11y ago
      It could probably be done with isochronous mode (http://www.beyondlogic.org/usbnutshell/usb4.shtml#Isochronous http://www.beyondlogic.org/usbnutshell/usb4.shtml#Isochronou...), but realistically it's easiest to just delegate all the real-time stuff to a $1 microcontroller on the other end of the USB link.
  - oxplot 11y ago
    After having a quick look at all the external interfaces of my laptop, the only one that has a predictable latency (that I know of) is the microphone/headphone jack. It should be fairly trivial to convert a serial digital data to an audio signal that can be reverted back on the other end. Of course, initially the jack latency needs to be measured (e.g. using a loop connection) and accounted for.
- RyJones 11y ago
  RS-232 is also how you get PPS off your GPS for maximum clock accuracy. emulated RS-232 over USB wasn't good enough as of a couple years ago

What about RS-232 and LPT?

by elcct 11y ago

What about RS-232 and LPT?

lsc 11y ago

I and most people in my job role carry usb -> DB9 rs232 dongles. doesn't work, of course, if you are trying to set up a serial console to debug the laptop, which is annoying, but it works fine for what we mostly use it for, which is to say, reading other serial consoles.

pjc50 11y ago

They're obsolete for consumer hardware and take up a lot of space, while a physical gigabit network port is extremely useful for low-latency high-throughput communication, such as to NAS. (RS-232 is still somewhat useful for hobby embedded stuff, but everyone just buys FTDI clone USB-serial cables)

monocasa 11y ago
Unfortunately the FTDI stuff (really any USB<->UART converter) has latency issues in the embedded space. : \
- seiferteric 11y ago
  I was wondering, would it be possible to create a better converter that did usb -> rs232/parallel port that had a special driver to put timing info? At least for driving CNC motors with a parallel port, timing is critical, you could send the pulse signal along with a timing, like 1 @ t0, 0 @ t0+1us etc.. Reading would be similar. The chip on the converter would have an accurate clock and faithfully reproduce the desired signal.
  - pjc50 11y ago
    It could probably be done with isochronous mode (http://www.beyondlogic.org/usbnutshell/usb4.shtml#Isochronous http://www.beyondlogic.org/usbnutshell/usb4.shtml#Isochronou...), but realistically it's easiest to just delegate all the real-time stuff to a $1 microcontroller on the other end of the USB link.
- oxplot 11y ago
  After having a quick look at all the external interfaces of my laptop, the only one that has a predictable latency (that I know of) is the microphone/headphone jack. It should be fairly trivial to convert a serial digital data to an audio signal that can be reverted back on the other end. Of course, initially the jack latency needs to be measured (e.g. using a loop connection) and accounted for.
RyJones 11y ago
RS-232 is also how you get PPS off your GPS for maximum clock accuracy. emulated RS-232 over USB wasn't good enough as of a couple years ago