Serial Port not open

General
1

Hi

I am getting the following error on a Raspberry pi 3 B+ when using the modbus node.

(node:747) UnhandledPromiseRejectionWarning: Error: Port is not open
at fs.write (/home/pi/.node-red/node_modules/@serialport/bindings/lib/unix-write.js:49:25)
at FSReqWrap.wrapper [as oncomplete] (fs.js:509:5)
(node:747) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 3)
(node:747) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
It is strange because this happens on a new Pi Zero W and an older Pi 3B+ but works fine on an older Pi Zero. I have tried older versions of Raspbian and NR, but cannot identfy why the one Zero works

Any help or advice appreciated

2

Does the user running Node-RED (pi I assume) belong to group "dialout" on the one that works and not the others? I doubt it though as I've just done a fresh install a week ago and my "pi" user is in the group without me adding it explicitly.

3

Thanks for the response, the pi user belongs to the "dialout" group on both

4

This is a longshot but as serialport uses native bindings, maybe it needs to be rebuilt (perhaps Node version has changed or something). You could try rebuilding it with:

cd .node-red
npm rebuild

Then restart NR.

Edit: also observe for possible build errors for the module

5

Thanks, tried that but error remains. I have gone through all my Pi's and now found another A+ that also works fine. The only common issue I can find is both have a similar version of node (10.16 and 10.17)
I have started again with a complete fresh install of Raspberry OS and NR but error the same

6

Sorry, I'm out of ideas. Hopefully someone else will have more things to try.

7

Thanks for your help, I am just cheating for now, I have taken the SD card out of the A+ and put it into the 3 B+ (where I need it) and it works, so I am just going to make a image of this SD and use that until I can find a solution.

Thanks again :wink:

8

Interesting but a working solution!

9

Which version of nodejs have you got on the new install?

10

I think I might have found the reason. It supports your findings:

NodeJS has dropped prebuilt binaries for NodeJS 10 and above for 32bit linux. As a result it's too difficult to maintain support. However if you build nodejs and serialport yourself it will probably work.

This might have a lot of implications...

11

Maybe it got something to do they changed by default the port names on pi3&4

Maybe you can try the chapter " Swapping the Serial Ports on Raspberry Pi 3 / 4" and see if it helps.

12

That would be a very good explanation. Have you checked this @mtoko?

13

Doesn't it compile it when you install the serial port anyway?

14

This reminded of me the fact I just ran across the fact that an USB serial interface might bind to either /dev/ttyAMA0 or /dev/ttyACM0 depending on the situation. I just tried the search icon on the serial in node and it offered me both options (I have a CC2531 zigbee2mqtt stick attached).

15

Yes but at least I've ran across a situation that I had to run npm rebuild after upgrading to a new major version of Node.

Edit: nevermind you were referring to the quote I sent. That is very true and it does compile fine on Node 14 on a 32-bit Raspbian for me.

16

I think the documentation I linked was actually referring to 32bit i386 builds of Node.js.

17

I don't think it applies to Raspbian (except possibly the Zero, where I think 10 is the last available).

18

You are all genius! @edje11 the document that you liked to solved the problem. I changed the config.txt and assigned the GPIO14 and 15 the "main" UART to AMA0 and that fixed the problem

Thank you to everyone :blush:

2 Likes
19

@colin luckily there are a good supply of unofficial builds still out there - https://unofficial-builds.nodejs.org/download/release

20

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