[Nut-upsdev] Adding drivers to NUT?

Gabriele TAORMINA gabriele.taormina at legrand.com
Tue Jul 24 15:26:38 BST 2018

Dear Daniele,

i understand perfectly, i'd like to explain you why we choosed to clone the blazer_usb driver:
some of our devices uses Voltronic Q1 protocol and we tried the Krauler Subdriver (it was the one with the right "commands", Q1, F, etc.), but the issues were 2:
- first: the Krauler Subdriver expects a different number of bytes in answer because in debug i see "Short Reply" (if i send Q1 to the UPS it will answer with 47 Bytes, CR terminated), from what i understand there is something wrong with the last byte that somewhere is not counted (because if i use a serial terminal and send Q1 the UPS answer correctly with the number of bytes required)
- second: the battery voltage low and high (estimated) were not acceptable for our UPSs because the % level will never reach the 100% and the voltage estimation was wrong.
- third: we have products with VID and PID: FFFF 0000, this is a problem because the combination is occuped by Krauler and in this way it will match each time with the wrong subdriver (krauler instead of our).

now the question i've for you: can we create a clone of nutdrv_qx, but with the differences shown before? do you have other solutions?
thanks for the support!

Best Regards,

Gabriele Taormina

UPS Strategic Business Unit

Field Application Engineer

Phone:     +39 0522/207046

Fax:           +39 0522/207005

Address:  Via Rodano 1 - Reggio Emilia - 42124 - Italy

Email:       gabriele.taormina at legrand.com<mailto:gabriele.taormina at legrand.com>

<mailto:gabriele.taormina at legrand.com>Website:  www.ups.legrand.com<http://www.ups.legrand.com/>

Website:  www.legrand.com<http://www.legrand.com/>


Da: Daniele Pezzini <hyouko at gmail.com>
Inviato: sabato 21 luglio 2018 02:48:25
A: Gabriele TAORMINA
Cc: nut-upsdev at alioth-lists.debian.net; Thierry DESTRUEL; Stefano PONGILUPPI
Oggetto: Re: [Nut-upsdev] Adding drivers to NUT?

aehm.. the innards of nutdrv_qx are not exactly well documented (and
vars have somewhat confusing names) -- my fault, sorry.
This is another thing that has been on my todo list for a while...

Briefly, at the moment, in nutdrv_qx, there are actually two kinds of
- 'protocols', which are communication-type-agnostic (i.e. they do not
fiddle with serial or USB operations, and are not restrained by them),
only map the protocol used by the device to the protocol used by NUT,
and are implemented in their own files using (and exposing only) the
`subdriver_t` format (for more info on this type, see the chapter of
the developer guide I mentioned before, 'nutdrv_qx.h' or the various
'nutdrv_qx_<name-of-the-protocol>.c' files),
- 'USB subdrivers', which only deal with USB I/O operations, and,
conversely, are implemented entirely in 'nutdrv_qx.c'.

With regard to 'protocols', nutdrv_qx works like this:
- 'nutdrv_qx.c''s `subdriver_list` lists the various (#include'd)
'protocols' the driver supports.
- Once nutdrv_qx has set up the communication with a supported device
in `upsdrv_initups()` (see below, for serial or USB devices), it gives
all (unless otherwise instructed by the user) 'protocols' in
`subdriver_list` a few tries by calling their 'claim()' function
(which usually tries to read some vars from the device to see if it's
actually 'speaking' that protocol): the first one to successfully
claim (i.e. the 'claim()' function returns 1) the device wins.
- From then on, nutdrv_qx uses that 'protocol' when communicating
(e.g. updating the vars, sending instant commands, ...) with the
device: the mapping in the 'qx2nut' table, the 'accepted'/'rejected'
strings, etc.

Now, onto communications (entirely in 'nutdrv_qx.c')...

For serial devices:
- given that, so far, all supported devices shared similar settings
and I/O modus operandi, operations are done directly without much
- setup is done directly in `upsdrv_initups()`,
- ditto for subsequent communications, in `qx_command()`.

For USB devices:
- `qx_usb_id` lists the various VID:PID pairs (with, optionally and
only if needed, the iManufacturer and iProduct strings) of each
supported device, coupled with a function ('fun()' from now on) that
will set `subdriver_command` to point to the function ('command()'
from now on) later used to communicate with the device.
- When nutdrv_qx starts, in `upsdrv_initups()`, it will either pick
the USB subdriver (whose name must be mapped to its relative
'command()' in the `usbsubdriver` list) directly if it was explicitly
provided by the user or, for each available USB device, traverse the
`qx_usb_id` lists, until it finds a match (VID:PID +
iManufacturer/iProduct) and then call its 'fun()' function -- in both
cases, the result is that, if a supported device is found,
`subdriver_command` points to the right 'command()' function.
- Later, every time nutdrv_qx needs to send anything to the device and
to get a reply from it (i.e. in the `qx_command()` function), it will
call the function ('command()') pointed to by `subdriver_command`:
this 'command()' function will receive a null-terminated byte string,
a buffer and its size, and will do all the needed things to a) send
the string to the device and b) get the reply from the device and
store it in the buffer (for example, sending the string verbatim to a
control endpoint and then reading the reply, or mapping the string it
gets to the index of a string descriptor, that, once retrieved, will
hold the reply).

A couple of examples worth a thousand words:
- adding a 'protocol':
- adding a 'USB subdriver':

Clearer, now?


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