Re: [time-nuts] USB to Serial Connectors for GPS Modules
Quoth Ulrich Bangert at 2008-06-05 13:58... consider the latency times of ANYTHING on a USB provided virtual serial connection to be in the order of 1 ms. If no serial data is send but only status signals change their state the latency can even be higher. Thanks (and to the others who responded to this). Just wanted to know where I was. I will make sure that I've got real serial ports with real kernel drivers for timing applications and use USB only for non time-critical stuff, like control messages, etc. (given a module with with 2 serial ports and only 1 port available on the house computer, for instance.) Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] USB to Serial Connectors for GPS Modules
At 04:10 PM 6/5/2008, Matthew Smith wrote: Quoth Ulrich Bangert at 2008-06-05 13:58... consider the latency times of ANYTHING on a USB provided virtual serial connection to be in the order of 1 ms. If no serial data is send but only status signals change their state the latency can even be higher. Thanks (and to the others who responded to this). Just wanted to know where I was. I will make sure that I've got real serial ports with real kernel drivers for timing applications and use USB only for non time-critical stuff, like control messages, etc. (given a module with with 2 serial ports and only 1 port available on the house computer, for instance.) Cheers M I wouldn't assume that the latency on a hardware serial port, depending on the OS, is any better than 1 ms, either. Particularly if you are expecting the process to be something like: value change on serial port line (Carrier Det) interrupt from hardware fielded by serial port ISR blocked process waiting on CD interrupt marked as ready to run indeterminate time waiting for next scheduler pass process starts running. While it might only take microseconds to fire up the ISR, it could be milliseconds before your process starts to run (unless you're using something at the device driver level?) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] USB to Serial Connectors for GPS Modules
Hi Folks Are there any issues with connecting computers to GPS modules through USB to serial devices like the FTDI FT232R, as opposed to 'native' serial ports? At the moment, I'm thinking in the context of an NTP server, but am interested in a general context should I need to move to USB-only PCs. Didn't know if there were any latency issues or anything. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] USB to Serial Connectors for GPS Modules
Matthew Smith wrote: Are there any issues with connecting computers to GPS modules through USB to serial devices like the FTDI FT232R, as opposed to 'native' serial ports? The PPS API (cf. RFC 2783) is generally implemented in the hardware serial driver (or is once the PPSKIT patches are applied, in the case of Linux). AFAIK, nobody has implemented the PPS API for USB serial drivers. You may see considerable jitter in your PPS timestamps. If you try it, consider measuring and reporting it along with latency. I've not seen any numbers. -ch ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] USB to Serial Connectors for GPS Modules
Usually, the adapters work fine. Two instances where they _may_ not: 1. Devices that are powered from unused serial lines. 2. Applications that perform direct twiddling of serial lines, instead of using host OS functions. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Matthew Smith Sent: Wednesday, June 04, 2008 6:26 PM To: Time Nuts List Subject: [time-nuts] USB to Serial Connectors for GPS Modules Hi Folks Are there any issues with connecting computers to GPS modules through USB to serial devices like the FTDI FT232R, as opposed to 'native' serial ports? At the moment, I'm thinking in the context of an NTP server, but am interested in a general context should I need to move to USB-only PCs. Didn't know if there were any latency issues or anything. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] USB to Serial Connectors for GPS Modules
Matthew, consider the latency times of ANYTHING on a USB provided virtual serial connection to be in the order of 1 ms. If no serial data is send but only status signals change their state the latency can even be higher. Best regards Ulrich Bangert -Ursprungliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Matthew Smith Gesendet: Donnerstag, 5. Juni 2008 03:26 An: Time Nuts List Betreff: [time-nuts] USB to Serial Connectors for GPS Modules Hi Folks Are there any issues with connecting computers to GPS modules through USB to serial devices like the FTDI FT232R, as opposed to 'native' serial ports? At the moment, I'm thinking in the context of an NTP server, but am interested in a general context should I need to move to USB-only PCs. Didn't know if there were any latency issues or anything. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi- bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
