USB to TTL Serial Cable issue
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USB to TTL Serial Cable issue

by doctorwho8 on Thu Oct 10, 2013 1:27 pm

Hello!
I bought on the beginning of the month from a dealer, Microcenter in Westchester County NY, this critter:
http://www.adafruit.com/products/954 Which is the USB to TTL Serial Cable. According to the site it uses the Prolific chipset.

Why? I don't know, and do not want to know. However the drivers that they write for Windows have a history of instability issues. I plugged it in this computer a total of twice so far. The first time was to confirm that it worked. Which it did.

The second time was to confirm that connecting it to the console setting on the Raspberry Pi (from a Makershed starter kit from last year) would provide me with a console. It did not. The messaging associated with any device that runs Linux crawled about half of the way down the program I was using and then nothing. In fact plugging it into my Linux computer caused its messaging to confirm that it was indeed working and came up as ttyUSB0 in the devices directory.

Connecting the Raspberry Pi back to power after bringing up a terminal screen on the Linux box who saw the serial connection caused me to end up with a proper Linux style console immediately the scrawl of start information ended. While I am not asking for support, I am indeed requesting that the good people back where Adafruit are located to please look into my statement and then issue an advisory of sorts.
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Re: USB to TTL Serial Cable issue

by adafruit_support_mike on Thu Oct 10, 2013 7:59 pm

When you say "The messaging associated with any device that runs Linux", I assume you mean the dmesg trace that gets dumped to the screen while the machine boots. I further assume you were connecting to the RasPi through `screen` or some other terminal emulator.

The fact that you saw the dmesg output means the cable works as it should. The RasPi boot sequence has a quirk where you need to hit a key once the dmesg trace ends before it will give you a login prompt.
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Re: USB to TTL Serial Cable issue

by doctorwho8 on Thu Oct 10, 2013 10:36 pm

adafruit_support_mike wrote:When you say "The messaging associated with any device that runs Linux", I assume you mean the dmesg trace that gets dumped to the screen while the machine boots. I further assume you were connecting to the RasPi through `screen` or some other terminal emulator.

The fact that you saw the dmesg output means the cable works as it should. The RasPi boot sequence has a quirk where you need to hit a key once the dmesg trace ends before it will give you a login prompt.


Hello!
To quote an old friend, "Quite Correct.". (Mr. Spock) Yes exactly, the Linux computer is indeed wearing the device, and its messaging indicated its was discovered. The RasPI did indeed make use of the USB device and told the emulator, I was using Putty in fact, to present me with what the device did on startup. And finally presented me with a logon prompt.

This did not happen with the suggested Windows driver. Now the important question, does Adafrauit plan on asking the chipset vendor about these issues? Or should I simply not worry?
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Re: USB to TTL Serial Cable issue

by adafruit_support_mike on Fri Oct 11, 2013 10:42 pm

When you say "this did not happen," which 'this' are you referring to: the dmesg crawl during boot, or the eventual 'press a key to log in' part?

If you get the dmesg crawl, both the cable and driver are working as they should. You may need to restart `putty` after the dmesg crawl ends because of some quirk in the way your machine handles the IO connection, but that's a userland issue, not a hardware or driver issue.
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Re: USB to TTL Serial Cable issue

by doctorwho8 on Fri Oct 11, 2013 10:56 pm

adafruit_support_mike wrote:When you say "this did not happen," which 'this' are you referring to: the dmesg crawl during boot, or the eventual 'press a key to log in' part?

If you get the dmesg crawl, both the cable and driver are working as they should. You may need to restart `putty` after the dmesg crawl ends because of some quirk in the way your machine handles the IO connection, but that's a userland issue, not a hardware or driver issue.


Hello!
The crawl ended before I got the login prompt up when using the linked Windows drivers on this laptop and I did indeed try to restart Putty. Also tried to restart things by unplugging the device and plugging it back in. It was not discovered, and Putty never did find it.

However the modules as drivers on my Slackware Linux version 13.37 found the device and that works. In this case Mike I did indeed get the dmesg crawl and was able to login.
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Re: USB to TTL Serial Cable issue

by adafruit_support_mike on Sun Oct 13, 2013 12:52 am

What version of Windows are you using? There could be a driver compatibility issue, though it isn't anything we've heard about before.
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Re: USB to TTL Serial Cable issue

by doctorwho8 on Sun Oct 13, 2013 1:06 am

adafruit_support_mike wrote:What version of Windows are you using? There could be a driver compatibility issue, though it isn't anything we've heard about before.


Hello!
Excellent question Mike.
This laptop runs Windows 7 Home Premium, the 64 Bit native variety.

There are stories on the site for the (now discontinued) NSLU2 device for Linksys, http://tech.groups.yahoo.com/group/nslu2-linux/?yguid=235165590 as it was discovered that the thing ran Linux, that the cables people were recommended for using for its serial ports, it was discovered that the Windows drivers for the gizmo that people chose, a Cell to computer cable, had instabilities. (Actual home page http://www.nslu2-linux.org/ .)

People were advised if they were going to do any work on their devices, they should either use a system running Linux, or failing that a Live-CD of such a system because of that. There was also some issues concerning the actual chipset itself, but that may have been falsely attributed.

Oddly enough the FTDI ones do not have that problem. I've used one such gadget originally made by Parallax for their Basic Stamp devices for hours without any problems, both for the Stamp kit, and for other uses.
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Re: USB to TTL Serial Cable issue

by adafruit_support_mike on Mon Oct 14, 2013 12:43 am

Again, if you see a dmesg crawl while the RasPi is booting, the cable is working as it should.

It isn't a complicated chip, generally speaking. It just converts USB data signals to TTL UART signals. It has no protocol sensitivity, and tends to be all-or-nothing in terms of functionality.

Some people have reported trouble with `putty` as the terminal emulator. Try using zterm.
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Re: USB to TTL Serial Cable issue

by doctorwho8 on Mon Oct 14, 2013 12:55 am

adafruit_support_mike wrote:Again, if you see a dmesg crawl while the RasPi is booting, the cable is working as it should.

It isn't a complicated chip, generally speaking. It just converts USB data signals to TTL UART signals. It has no protocol sensitivity, and tends to be all-or-nothing in terms of functionality.

Some people have reported trouble with `putty` as the terminal emulator. Try using zterm.


Hello!
Zterm is only available for the Mac. I'm running Windows here. And on the Linux computer, Putty was also built for that OS.

What problems were reported? I do know that its telnet implementation can be a bit unfriendly as applied to emulators of computer systems.

Besides, currently on the Linux system everything is working as expected so therefore the cable works. Why things didn't here is another matter. And one I'm willing to drop for the time being.
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