[Thumbgps-devel] USB handshake signals and Linux

[Ron Frazier (NTP)]

PS, I did have to issue some commands using stty, which I cannot 
remember at the moment.  Setting baud rate was one thing.  That wasn't 
all of it though.

Sincerely,

Ron

On 3/14/2012 8:55 AM, Ron Frazier (NTP) wrote:
> My GlobalSat BU-353 has an internal Prolific serial - USB converter.  
> It pretty much worked out of the box in Ubuntu 11.04 without 
> installing any drivers, although some drivers are available on the 
> GlobalSat website.  And, I'm only communicating with it, at the 
> moment, using NTPD, not GPSD.  I'm running windows at the moment, so I 
> cannot look at that config file.  However, I think it appears as 
> /dev/ttyUSB0 or something, then I had to make a symbolic link to 
> /dev/gps5 (which is equivalent to running on COM5 in windows).
>
> I have a sure electronics GPS demo board on order.  I have to solder a 
> wire on the board to get PPS to the DCD pin, and hopefully not kill 
> the board.  Once that's done, I'm going to be testing PPS through an 
> external Prolific based adapter, the Trendnet TU-S9.  The packaging 
> specifically says it passes signals on all pins of the DB9 connector.  
> The reviews on this adapter on Amazon.com are good, some of which 
> mention linux.  My first testing will be on windows, then linux.
>
> For those of you who may not be familiar with the NTP Questions list, 
> there is a good bit of discussion on this list about GPS, perhaps more 
> so since I've been asking questions about problems I've been having.  
> While not specific to your project, the info that comes across the 
> list might be helpful.
>
> http://lists.ntp.org/listinfo/questions - NTP Questions List
> http://lists.ntp.org/pipermail/questions/ - archives
>
> Sincerely,
>
> Ron
>
> On 3/14/2012 6:49 AM, Eric S. Raymond wrote:
>> Since the Plane Jane design concept depends on the host system being
>> able to see USB events corresponding to serial handshaking state
>> changes, I went looking for information on which handshake signals
>> from which serial-to-USB adapters actually propagate these signals
>> through. I focused on Linux becase that's the kernel for the
>> bufferbloat deployment.
>>
>> My list of adapters is taken from the gpsd udev rules file. This
>> enumerates all the USB-to-serial chips we've observed in the wild
>> since 2005. Note that the PL2303 is by far the most common, with
>> 15 of 20 device types for which we know the USB chip using
>> it. Weighted by device volume the PL2303's share would be far higher.
>>
>> PL2303: From source/linux/drivers/usb/serial/pl2303.c in 2.6.11.8,
>> there are defines UART_DCD, UART_RING, UART_CTS and UART_DSR and code
>> to implement looking at these signals in the TIOCMGET and TIOCMIWAIT
>> ioctl handlers.  A bug fix for TIOCMIWAIT was merged in 2006.
>>
>> FTDI SIO: (8U232AM / FT232): There is a comment in the kernel source
>> file drivers/usb/serial/ftdi_sio.c from 2.6, in the implementation of
>> TIOCMIWAIT, that specifically says "Wait for any of the 4 modem inputs
>> (DCD,RI,DSR,CTS) to change". I found no bug reports or fixes relating
>> to this feature.
>>
>> Cypress M8/CY7C64013: Like the FTDI; TIOCMIWAIT is implemented for
>> all four handshake lines.  I found no bugs relating to this feature.
>>
>> Cygnal Integrated Products, Inc. CP210x: Like the FTDI and Cypress M8;
>> TIOCMIWAIT is implemented for all four handshake lines. The code was
>> reworked in 2010.
>>
>> Note: there is a known TIOCMIWAIT bug in the *device-independent* part
>> of the serial-device layer: speed or other serial-parameter changes
>> during a TIOCMIWAIT call will hang it. GPSD has had to work around
>> this.
>>
>> Conclusion: if we can get 1PPS to the input side of any of these
>> adapters, the Linux host will be able to see it.
>


-- 

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Ron Frazier
timekeepingdude AT c3energy.com