On Wed, Aug 7, 2019 at 11:04 AM Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote: > > On Wed, Aug 07, 2019 at 09:48:03AM -0400, Robert Middleton wrote: > > > I'll try to get some firm results in the morning; otherwise I won't be > > > able to check until early next week as I will be away from the > > > hardware. > > > > After doing more testing, I think that I finally have something that > > is working fully at all baud rates. I've tested this at > > 115200,9600,and 4800, testing via: echo "the quick brown fox jumps > > over the lazy dog" > /dev/ttySx > > > > Removing the check to uart_circ_empty in the while loop makes it more > > reliable, however it will occasionally fail and only transmit the > > first part of the message(at 4800, it will transmit only "t", at > > 115200 it will transmit "the quick bro"). > > I'm not sure about the loop for uart_circ_empty(). Can you try 2-3 kB of text > at lower baud rate, let's say 2400 or so? So at the lower baud rate, it does not transmit all of the data, probably because the timeout eventually stops it. However, it does get back into a very weird state that I have seen before, where opening up the port again will cause it to transmit some of the previously-buffered data. See below for some more details. > > I've found that breaking it > > into two loops, one checking the uart_circ_empty and the other doing > > the LSR check is reliable at all baud rates. > > If my suspicion is correct, the shutdown of the port will take ages which is > inappropriate. The shutdown probably does take a while, but the fact that not all of the data is transmitted is what tripped me up in the first place and sent me down this track trying to figure out why all of the data was not being transmitted out of the serial port properly. The previous hardware used an FTDI USB to serial converter to send serial data, and changing to the exar caused some of our applications to stop working. They do a similar thing to echoing from the terminal, that is they come up, send a command, and then exit. I tried just now with an FTDI cable and got some interesting results vs. using the exar. The data(3kB) gets fully transmitted when I do 'cat lorem-ipsum.txt > /dev/ttyUSB0', but when I do it via 'cat lorem-ipsum.txt > /dev/exar-serial' it will timeout after a second. Doing an 'echo "" > /dev/exar-serial' will send more of the text, until it stops again. I have to do this about 5 times before all of the data gets transmitted over the serial port. This is also at 2400 baud on both the exar and the FTDI. At this point, this leads me to believe that there is actually a more fundamental problem with the 8250 driver and flushing data. I was focusing more on the exar, since that is the only hardware that I have available that uses the 8250 driver. -Robert Middleton
