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favalex / modbus-cli

Command line tool to access Modbus devices
Mozilla Public License 2.0
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"Mixed Endian" encoding #1

Closed FloRinke closed 3 years ago

FloRinke commented 6 years ago

Some vendors use a "mixed endian" encoding, where the registers of multi-register data types are swapped. This can not currently be accessed using modbus-cli.

Are you interested in a pull request? (Which commit should I base my work on? Current head seems not to work for me)

FloRinke commented 6 years ago

By "mixed endian" I mean the following:
Lets use a 4-byte Integer with value 0x11223344 The way modbus-cli currently encodes this into registers is: [0x11,0x22] [0x33,0x44] The "Mixed Endian" encoding would be [0x33,0x44], [0x11,22], so regular big endian registers, but registers arranged in a little endian way...

I don't really like this, but unfortunately I've got a device which insists on this structure...

favalex commented 5 years ago

Yes please, if you are still interested after all this time, feel free to open a PR to support mixed endianness.

I've just pushed a fix to master, it should work now and you can fork from there.

dequis commented 3 years ago

Hey there! I'm also interested in implementing this feature, and was going to ask, what should the UI look like?

I was wondering if it should be flexible for different ways to mess it up, but considering that we have two different devices from different vendors that have the same kind of mixed endian as what the OP of this ticket described, I guess a single toggle switch -m --mixed-endian for reading standard big endian registers and re-packing them as little endian could be enough?

FloRinke commented 3 years ago

I did not pursue this any further, as the problematic device turned out to be unsuitable for my purpose for other reasons. Before this I had it somewhat working, but based on the older, non-modularized code (as the newer one did not run at that time). I can have a look, this should still be laying around somewhere.

favalex commented 3 years ago

@dequis what do you think of a --byte-order=le|be|mixed argument? We could also accept any order with syntax like --byte-order=2134 (with be etc. as alias for 1234)

dequis commented 3 years ago

what do you think of a --byte-order=le|be|mixed argument?

Sure!

We could also accept any order with syntax like --byte-order=2134 (with be etc. as alias for 1234)

Thaaat gets a bit more complicated when you want to cover both 32bit and 64bit fields, where you'd have to express (for example) both 3412 and 78563412

favalex commented 3 years ago

True. We don't have any proof of byte orders other than le, be and mixed being used. So I'd say for now let's keep it simple and forget about the 3421 syntax.

favalex commented 3 years ago

Solved by https://github.com/favalex/modbus-cli/pull/13 Thanks @dequis !