ex. watchdog by serial communication or time in while

erpgc82 · Joined: 02 May 2020 Posts: 73

Hello friends, I'm trying a problem with the first program I made and put on a PC system.

The PIC18F46k22 receives a string from the PC, with a fixed number of characters, it happens that, every 50 tests I do, the microcontroller crashes, and it only works again when I turn it off and on again. If it was a different length string, I could handle it, but it's not.

So I thought of WatchDog, but I have no experience. Can anyone give me an example?

I just use Fuse

temtronic · Posted: Wed Mar 16, 2022 12:46 pm

bdeb · Joined: 05 Nov 2010 Posts: 42 Location: Sweden

Dear erpgc82,

I'm not a guru, but have used & loved the 46K22 and found it stable.

I assume you followed "ex_sisr.c" example of how to receive data.
May your buffer be too small for a "strange" message from your PC?

Try using other UART for debug or set an LED on buffer overflow.

Best of luck:

/BdeB

erpgc82 · Joined: 02 May 2020 Posts: 73

Hello friend, yes I use a Buffer, I'm working with 26 bytes of characters and the buffer is 64 bytes.

Yes, as soon as the string ends, at the end I enter the '0' or '\0' by the way, it's very similar to the C++ I'm studying at the moment.

ok, i will post a piece here as soon as possible.

That's what I also thought that a Watchdog works, if it doesn't check the "while" of the "main()" function within a certain period of milliseconds, it would restart the program.

In a test I did, I noticed that the program restarts completely, as if it had disconnected from the mains and then reconnected. Is there a way for Watchdog to act, without having to restart the main function? In short, just unlock.

Very good, my God, the 115200, excellent!

erpgc82 · Joined: 02 May 2020 Posts: 73

Good tip, I'll do it! The PIC18F46K22 is really big and stable, I really didn't understand until now what's going on, so I thought of Watchdog, which I've never used, I'm new to programming.

temtronic · Posted: Wed Mar 16, 2022 5:28 pm

Consider the 'Watchdog' as a hardware 'cold reboot' used when the program takes too long to do a normal 'loop' of operations. When it 'times out', it forces the PIC to restart, from the beginning, just like a power off/power on sequence does.
That is how it's supposed to work.

Now there is a solution for when your serial data (26 bytes) doesn't all come in as planned. The CCS manual in the 'commonly asked questions' chapter or FAQ section, has a 'serial input with timeout' Q&A. It allows for a preset time period for the PIC to receive data from some source. You'll need to do some 'math' to fine tune the 'timeout' value. 9600 baud is +-960 characters per second, so a 'stream' of 26 characters takes about 1/40th of a second, say 25ms. double that = 50 ms.
So a timeout of 50 ms will allow the PIC to stay in the receive loop until either all 26 characters have come in OR the 50ms time has elapsed.
You can make the timeout value less (closer to 26ms) so the PIC will exit (return to main program), faster BUT it needs to be long enough for the PIC to store the data into a buffer, set flags, etc.

9600 baud is about 1 character per 1 millisecond. My math be not be correct, will be 69 this year...

Ttelmah · Joined: 11 Mar 2010 Posts: 19503

and, this is where 'restart_cause' comes in.

If you declare variables 'uninitialised', you can have code like: