Re: Serial port error statistics - any comparable data?
Diez B. Roggisch wrote: if you have the chance, try attach a machine with legacy rs232 port, and see if the errors still remain. Additionally, what kind of buffers does your device have? I'm using pyserial to control a very sensitive device with nuttily implemented buffering strategy. It has a fast and a slow buffer which are filled in order, and no signalling to the outside sender on how full they are. If the fast buffer fills the slow buffer kicks in and requires less transmission rate. That may be how characters could be lost with you. Regards, Björn -- BOFH excuse #119: evil hackers from Serbia. -- http://mail.python.org/mailman/listinfo/python-list
Re: Serial port error statistics - any comparable data?
Diez B. Roggisch wrote: RS232 is unfortunately as bad as a protocol as it can get. I've used it for communication with a microcontroller for just a few bytes every second. And it failed miserably, so I needed to implement a protocol on top of it. We normally do this anyway, except for stuff like menus that are intended for interactive use as setup - doing without on machine to machine comms feels a bit too cowboy... The machine spec is totally irrelevant - what is interesting is the serial hardware you use. Are you by any chance using a serial2usb-converter? I had nothing but troubles with these. I have also heard rumours about this, and you have just hardened my admittedly irrational attitude towards them. I have never used one in anger. if you have the chance, try attach a machine with legacy rs232 port, and see if the errors still remain. Diez Alas - the port in question is the native legacy motherboard port. If it were windows, it would be COM1... I had hoped that somebody would have done some similar work, so that we could compare notes on the error frequency. It does not seem likely though - If I was not testing the performance of the Lantronix xport device, I would not have kept stats either - it is kind of tedious to sit and watch the fox scroll up the screen for days on end.. It just surprised me to find that the errors were made in the PC's receive. I proved this by short circuiting the xport's receive and transmit at the RS-232 level and gave up after some ten million error free lines. (Most of an afternoon, overnight, and most of the next morning ;-( ) thanks Diez. Then Castironpi wrote: Transmit observed minus expected to cluster. The cluster in all the cases observed is the loss of exactly one character, somewhere from around more or less the middle of the string: The quick brown fox jumps over the lazy dog 0123456789 Why do you make the assertion that the errors would cluster? What kind of tables does the input device build? Whatever the kernel and the cpython implementation does to receive the string from a port unblocked with fcntl - and the throw away python script that does the echoing builds the string up with a read(1). And before I get flamed for wasting resources - The read(1) is necessary to be able to run a protocol, later. - Hendrik -- http://mail.python.org/mailman/listinfo/python-list
Re: Serial port error statistics - any comparable data?
On Sunday 30 March 2008 12:19:58 Bjoern Schliessmann wrote: Diez B. Roggisch wrote: if you have the chance, try attach a machine with legacy rs232 port, and see if the errors still remain. Additionally, what kind of buffers does your device have? I'm using pyserial to control a very sensitive device with nuttily implemented buffering strategy. It has a fast and a slow buffer which are filled in order, and no signalling to the outside sender on how full they are. If the fast buffer fills the slow buffer kicks in and requires less transmission rate. That may be how characters could be lost with you. Regards, Bjoern That is a horrible device - have they not heard of RTS / CTS? or even XON / XOFF ? It is a wonder that you got that working without turning into an axe murderer. I don't think I could have. I have not been exactly forthcoming about the setup - the device in question sits on the LAN, so I connect to it via a TCP socket connection (in either client or server mode - seems to make no difference) . On the other side of the device, there is a serial port, and another PC is connected to the RS-232 side. This is the PC that runs a simple echo script that makes the occasional error, on its receive - I can see this because the transmission is paused when I see an error, and the two strings are identical on the two machines. As I mentioned in my reply to Diez and Castironpi - its not the device that is making the errors, as proved by a simple loopback. Another interesting statistic is that the number of lines in flight on the round trip machine1 xport machine2 xport machine 1 due to buffering varies between about 4 and about 26. So much for using it for real time control... - Hendrik -- http://mail.python.org/mailman/listinfo/python-list
Re: Serial port error statistics - any comparable data?
On Sat, 29 Mar 2008 13:14:46 +0200, Hendrik van Rooyen wrote: Hi, I have been doing some tests on a device that we are thinking of incorporating into a product, and I have seen that reception on a serial port at 115200 baud over about six metres of RS-232 cable makes mistakes, to the order of 125 lines with errors in them out of approximately 18.4 million lines of 65 or so chars - about one errored line in 147000, or one error character in 95 million. The PC that is making the errors is a 64 bit dual core AMD machine running at 2 Gig, and I am running stock standard Open Suse 10.3 with the supplied Python 2.5. What kind of bothers me is the nature of the errors - I seem to get only missing characters, as if an interrupt was missed. There are no munged characters as one would expect if the errors were bit related. Has anyone else seen anything like this, and am I worrying needlessly? I realise that my production protocols will easily handle this almost non existent level of error - but if this were in microcontroller code that I had written myself, I would suspect that I was spending too long in some critical section of code. - Hendrik Have you verified that you have flow control enabled? ISTR hearing there is one kind of software flow control and two kinds of hardware flow control. I'm not serial expert, but ISTR that if your cable supports it, you should use RTS/CTS hardware flow control, and if it doesn't, use software flow control. -- http://mail.python.org/mailman/listinfo/python-list
Serial port error statistics - any comparable data?
Hi, I have been doing some tests on a device that we are thinking of incorporating into a product, and I have seen that reception on a serial port at 115200 baud over about six metres of RS-232 cable makes mistakes, to the order of 125 lines with errors in them out of approximately 18.4 million lines of 65 or so chars - about one errored line in 147000, or one error character in 95 million. The PC that is making the errors is a 64 bit dual core AMD machine running at 2 Gig, and I am running stock standard Open Suse 10.3 with the supplied Python 2.5. What kind of bothers me is the nature of the errors - I seem to get only missing characters, as if an interrupt was missed. There are no munged characters as one would expect if the errors were bit related. Has anyone else seen anything like this, and am I worrying needlessly? I realise that my production protocols will easily handle this almost non existent level of error - but if this were in microcontroller code that I had written myself, I would suspect that I was spending too long in some critical section of code. - Hendrik -- http://mail.python.org/mailman/listinfo/python-list
Re: Serial port error statistics - any comparable data?
Hendrik van Rooyen schrieb: Hi, I have been doing some tests on a device that we are thinking of incorporating into a product, and I have seen that reception on a serial port at 115200 baud over about six metres of RS-232 cable makes mistakes, to the order of 125 lines with errors in them out of approximately 18.4 million lines of 65 or so chars - about one errored line in 147000, or one error character in 95 million. The PC that is making the errors is a 64 bit dual core AMD machine running at 2 Gig, and I am running stock standard Open Suse 10.3 with the supplied Python 2.5. What kind of bothers me is the nature of the errors - I seem to get only missing characters, as if an interrupt was missed. There are no munged characters as one would expect if the errors were bit related. Has anyone else seen anything like this, and am I worrying needlessly? I realise that my production protocols will easily handle this almost non existent level of error - but if this were in microcontroller code that I had written myself, I would suspect that I was spending too long in some critical section of code. RS232 is unfortunately as bad as a protocol as it can get. I've used it for communication with a microcontroller for just a few bytes every second. And it failed miserably, so I needed to implement a protocol on top of it. The machine spec is totally irrelevant - what is interesting is the serial hardware you use. Are you by any chance using a serial2usb-converter? I had nothing but troubles with these. if you have the chance, try attach a machine with legacy rs232 port, and see if the errors still remain. Diez -- http://mail.python.org/mailman/listinfo/python-list
Re: Serial port error statistics - any comparable data?
On Mar 29, 4:26 pm, Diez B. Roggisch [EMAIL PROTECTED] wrote: Hendrik van Rooyen schrieb: Hi, I have been doing some tests on a device that we are thinking of incorporating into a product, and I have seen that reception on a serial port at 115200 baud over about six metres of RS-232 cable makes mistakes, to the order of 125 lines with errors in them out of approximately 18.4 million lines of 65 or so chars - about one errored line in 147000, or one error character in 95 million. The PC that is making the errors is a 64 bit dual core AMD machine running at 2 Gig, and I am running stock standard Open Suse 10.3 with the supplied Python 2.5. What kind of bothers me is the nature of the errors - I seem to get only missing characters, as if an interrupt was missed. There are no munged characters as one would expect if the errors were bit related. Has anyone else seen anything like this, and am I worrying needlessly? I realise that my production protocols will easily handle this almost non existent level of error - but if this were in microcontroller code that I had written myself, I would suspect that I was spending too long in some critical section of code. RS232 is unfortunately as bad as a protocol as it can get. I've used it for communication with a microcontroller for just a few bytes every second. And it failed miserably, so I needed to implement a protocol on top of it. The machine spec is totally irrelevant - what is interesting is the serial hardware you use. Are you by any chance using a serial2usb-converter? I had nothing but troubles with these. if you have the chance, try attach a machine with legacy rs232 port, and see if the errors still remain. Transmit observed minus expected to cluster. What kind of tables does the input device build? -- http://mail.python.org/mailman/listinfo/python-list
