Servo driven axis + Step/Dir 4th/5th axis

Hi guys,

I've been wondering if it's possible to add a 4th and/or 5th axis of Step/Dir type to a CNC which has Servo driven axis.
I'm (planning on) using a 7i92 + 7i77 (+ 7i84 for button interface) mesa cards combo and the idea would be to just add a 7i78 card (Step/Dir interface) to the config so I can add a 4th and/or 5th axis using a couple of spare drives I have.

I've researched a bit and, in terms of trajectory planning LinuxCNC doesn't care what type of drive the axis has (which makes sense) and that part is handled by the HAL connections, but I'm just not sure if it's possible to configure the Mesa's SmartSerial (SS) connection to be able to do this.

Thanks in advance,
Simão A.

The 7i78 would connect via the 2nd connector on the 7i92, so all you would need is a bit fie to suit. If you have a look at the 7i78 manual you'll see the DB25 connections for the step\dir signals.
So you'd have a smart serial channel on the 7i77 and a smart serial channel on the 7i78.

I have a 7i92 as well, have a 7i76 connected to one connector and a 7i74 connected on the other connector. (I only get 6 channels from the 7i74, I think that is a fpga limitation)
Loading the driver with the right config everything is fine.

Thanks for the reply BeagleBrainz!

Well in my case, I've previously used the spare smart serial connection (rs422/485) of the 7i77 to connect the 7i84 (saved money on the 7i74) and it works like a charm, so I guess I can then just use the second 7i92 connector for the 7i78.

AFAIK, you can only use 6 channels of your 7i74 because the 7i76 uses 2 SS channels, and I think all channels are shared between the two 7i92 connectors, they are just there to make it easier for splitting connections (I'm not 100% sure, I have to confirm this)

Good point there, never considered that. Either way it's not a issue in my case. I needed an extra smart serial channel, so I'll have a few spares.

I think this for the reason for my thinking.
Each Anything-IO board can attach up to 8 sserial remotes to each header (either the 5-pin headers on the 5i20/5i22/5i23/7i43 or the 25-pin connectors on the 5i25, 6i25 and 7i80). The remotes are grouped into "ports" of up to 8 "channels". Typically each header will be a single 8 channel port, but this is not necessarily always the case.

Basically the reason you get only 6 SSerial channels on the 7I74 of a 7I77/7I74
7I92 configuration is that all FPGA resources are used and there is only
room for a single SSerial port with 8 total channels. With a larger FPGA,
there is room for additional SSerial ports. Adding a channel is not much
space but adding a new port is a large jump due to the fact the each port
is independent,with its own CPU,RAM/ROM/ host interface/timers etc.

Ok, so far I think it's pretty safe to say that, hardware wise, it's doable, but what about the software configuration part? Is it possible to configure a serial port for a different driver type? (meaning, 7i77 on the first port and 7i78 on the second port)

Also, how does the Mesa driver work on the HAL layer? does it need to know the configuration of the board (I/Os, addresses, etc) prior to initialization (from some config file, or hardcoded) or does it poll from the actual cards during initialization?? (dynamic config)

Mesa FPGA card and SSerial card initialization is dynamic
That is, appropriate hal pins will be created depending on the
discovered hardware. You can specify some options on the driver
command line for example the number of Stepgens, PWMGens
sserial ports, etc and sserial port modes.

The hostmot2 manual describes this (and shows all available modules)

BTW the firmware for a 7I92 with 7I77 and 7I78 is 7i92_7i77_7i78d.bit

Thank you for the explanations PCW!

BTW the firmware for a 7I92 with 7I77 and 7I78 is 7i92_7i77_7i78d.bit

That's exactly what I wanted to know! Well if there is a firmware for it then I'll give it a go!

Thank you all,

Best regards,
Simão A.

www.mesanet.com/software/parallel/7i92.zip

in configs/hostmot2