On 5/21/17 11:20 AM, Chris Albertson wrote:
The problem is that you get the ENTIRE string then parse it. This is
not going to work well as you found out. Your CPU spends almost the
entire time waiting for characters to come in slowly off the serial
line. You are just waiting on bits and wasting CPU cycles
On many Arduinos these days, the "getSerialString()" is a
buffered/interrupt driven routine under the hood - it's not burning many
cycles.
That said, even if your serial port code was "spin on a bit", you can do
a lot of parsing/processing pretty quickly. Arduinos aren't 4 MHz Z80s
or 8051s. The modern crop have 50 MHz clocks and a millisecond is a lot
of instructions.
What you need to do is parse one character at a time. I bet your
parser reads one character at a time from the string. Have it read
one character at a time directly from the serial port. (Use a state
machine. It will work for such a simple job as this)
Yes if your CPU was MUCH faster your plan could work. But on some
GPSes the data never has a break. You are trying to do ALL the work
in the break but actually most of the down time when you should be
working is between the characters. There is not a lot of work a
finite state machine needs to do between characters, just move state
based on a 'character class" table.
I think that would be overkill, it's a lot harder to write a state
machine than a simple "is the first N characters $GPPGA?" kind of thing.
You'd want to write a generalized parser first if only to make sure that
you're decoding the strings properly. You'd run your arduino code with
a "getSerialString()" then a "Serial.print(str)" in a loop, then cut and
paste from the console display into a file, then run your decoder
against it.
I you ever studied this
formally, what you are building here is a "lexer" not a parcer. The
"Language" is not recursive and you never need to backtrack so it can
be de-coded literally one character at a time.
You DO really want the 1PPS to drive an interrupt. Thisway you just
continue working on the data stream and don't wait for the PPS. When
the PPS happens you do something QUICK. never do anything time
consuming in the ISR or you will miss the next serial character.
increment a seconds count and write two bytes the the LCD and exit
Thats what the Arduino "AttachInterrupt()" is for
attachInterrupt(digitalPinToInterrupt(pin), ISR, mode);
where mode is probably going to be "RISING".
Nothing fancy in the ISR, just a "1ppsdetected++;" or something.
then in the void loop(), you do a test on 1ppsdetected
if (1ppsdetected>0){
1ppsdetected = 0;
update_display();
}
On Sun, May 21, 2017 at 6:45 AM, Ben Hall <[email protected]> wrote:
Good morning all,
A quick update for those interested on my Arduino code development for the
TruePosition boards. I've got Arduino code together than can read in the
serial stream, parse it, and display time, date, number of satellites, and
TFOM on a 2x16 LCD display. It does not do multiple screens, handle survey,
or display lat/long yet.
What I'm having issues with is handling the 1 PPS. Ideally, I want to use
the 1PPS signal to trigger the display update. IE:
void loop()
{
getSerialString() // uses serial.available to pull in the serial data
parser() // this parses the data
wait for 1PPS tick to go high
if there has been a clock message, updateDispay() // update the display
}
This works great when there is a just a clock message. But when there is a
clock message, an extstatus message, and a status message, it seems like it
is still parsing when the 1PPS tick comes in...so it will display seconds as
follows: 30, 31, 33, 34, 35, 36, 37, 39, etc...
(If I don't wait for the 1PPS tick, it seems that my clock is one second
fast. I say "seems" to be fast, as the time agrees with an NTP clock on one
computer, but seems a half second slow per GPSCon's time display on the
Z3801. I think I need to put up the antenna and check against WWV.)
I've got one of those cheap little USB logic analyzers on order to figure
out how much time elapses between the clock, extstatus, status, and 1PPS
tick. I may need something faster than an Arduino Uno to do this.
I'm sure there is a way to do this with an interrupt...but I couldn't make
that work yesterday. More to follow.
thanks much and 73,
ben, kd5byb
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