I hope to add applicable scenarios for the modbus_reply() function.

[SupermanOfHeiLinPu]

I want to write a Modbus slave software, but my register layout is as follows: [0, 5]: Input registers; [6, 10]: Holding registers; [11, 15]: Input registers; [16, 20]: Holding registers. In this case, the provided modbus_mapping_t and modbus_reply() functions in the library cannot achieve this functionality. I think we can write another modbus_reply() function that uses a callback mechanism to retrieve and set data.

[nazaryev-cool]

Since 2013, there have been five attempts to add callbacks or user-defined functions to modbus_reply():

• Introduce support for callback functions #140 (2013)
• New function modbus_reply_callback() #319 (2016)
• Callback-API for modbus slaves #323 (2016)
• Add modbus_reply_callback() and modbus_set_reply_callback() #408 (2017, ntfreak@322ea2b)
• Users functions #522 (2020)

Sadly, none of these were successful for some reason.
@stephane, can you explain why these attempts failed? What can be done to fix or rewrite them so they can finally be merged into the main branch?

[stephane]

Thank you for the list of callback PRs. One of them is also stored on my computer...
No reason excepted time to work on it.
I received a new contract that will help.