to have the interrupt routine call the print routine? This is my GPS Clock sketch, the date isn't fixed yet but that is small. The interrupt runs all the time and greatly interferes with printing the data to the LCD. These are two of Adafruit's sketches combined they display data from a GPS receiver on a ST7735 display I bought from Adafruit. Unfortunately I get lost real quick trying to understand what is going on in the setup routines for the GPS and the first third of the Loop.
If you are sure that you won't fill the internal buffer of 64 bytes, and you don't mind that the output will appear only long after you left the interrupt routine, your sketch might survive, though ...
In general "Keep the ISR small and fast" and doing Serial stuff does not go together.
Thank you for the information. It still seems to me that If the ISR called the serial routine to output data I would have a more stable display. it would take about 300 mS for the whole thing to happen, then in the remaining time left in a second it can parse looking for the updated time data. The next or new second, I don't care about the Nav data at all
(I've not tried anything except the display... Yet)
I sure would like that sketch to parse that stream of data from the GPS less often somewhat less often or figure out a way to make it quiet long enough to write the display. The next option is to send it to another Proc for it's ultimate use and I'd rather not waste a chip If I can help it. I've got plenty of chips and boards but the main issue is simply an efficient method of solving the problem.
Data from GPS comes via some Serial port usually, and you want to write to another Serial port.
I checked the GPS Test examples Adafruit refers to: using Serial and SoftSerial to log time and more ...
I don't see where there are interrupts involved (except eventually inside the Serial libraries) and what you want to accomplish by using interrupts.
Michael the code I used from Adafruit examples/parsing/parsing.pde is perhaps not the greatest sketch to display time with. It updates the time every 2 seconds + the overhead for parsing and displaying the data so the seconds data increments about every 2300 mS +/- 50 mS . It takes about 280 - 320 mS to clear and write the new data to the display, why the time differential of 50 mS is present is a great mystery to me. I did at one time set a timer and measure the time necessary to fill the screen or clear the data and write new data. The difference in the screen display time shouldn't be present and it was my "assumption" that because of a "Mentioned" interrupt the sketch was servicing the "interrupt" during the screen display task and in fact it does about every third time display a line one character at a time slowly instead of the "normal" blink... blink... blink of writing a line at a time. This happens anywhere in the display routine from the fill screen call to writing any of the text so I again "assumed" that the routine was running with an interrupt and it was parsing data from the GPS serial data when it was writing the display and this is not what I want or need. The sketch is not well written as it updates the seconds data every ~2+ seconds. It is my thought that it was only intended as a tool to prove the GPS device is functioning. I think my error is in trying to use code that I don't understand and probably unless I get real lucky with this one I need to find a sketch I understand and use it. I frequently state that my total knowledge of C and C++ is slightly more than can be written legibly on the head of a pin. I learn a little more every day but it goes much more slowly than I like. I started in March of this year with some Basic and PIC assembler experience and this is only as far as I have been able to go. I got thoroughly lost and asked for help without really knowing what help to ask for. In review of the responses to the question and my attempts at a working sketch leave me at the point of looking for a better GPS library than the one I am using or learn to write my own. I certainly don't expect more than a suggestion as to where I might look to fix my issues and I have it now. Find something I can understand and make it work. FYI this was meant to be a time server for a larger project I am trying to make for myself basically a clock and a "Mini" weather station... with X10 control added so I could turn on lights at scheduled times of the day or other control based on Time, Temperature or Humidity. It is intended to be open ended so I can expand it as I see new possibilities or find new requirements.
This is also a retirement project for me, an attempt to manage my time in a personally interesting and challenging manner.
So I thank You Sir, for your time in considering my poorly formed question and trying to formulate an answer for me.