Custom PCB / Application questions

Robert Bouillon

I'm creating my own PCB on which to mount the Omega 2.

Is there a datasheet I can reference? docs.onion.io is a little lean as far as specifications go.

I have these questions specifically:

How do I properly connect the RST and FW_RST to a switch? Do I just need to sink them to ground? Do I need a resistor / Pull-up / Pull-Down? What's the difference between the RST and FW_RST?
Is it okay to leave the unused pins hanging? What are the minimum connections?
What's the purpose of VOUT? Should I connect this to my 3.3v supply?
It looks like SPI is driven by software on any GPIO port. Is it safe to repurpose ANY green GPIO port for SPI? What speeds are supported for SPI?
What's the nominal / max / inrush current draw? Is a 300mA regulator sufficient?

Thanks.
--ROBERT

WereCatf

@Robert-Bouillon said in Custom PCB / Application questions:

Is there a datasheet I can reference? docs.onion.io is a little lean as far as specifications go.

See https://github.com/OnionIoT/technical-drawings/tree/master/Mechanical

How do I properly connect the RST and FW_RST to a switch? Do I just need to sink them to ground? Do I need a resistor / Pull-up / Pull-Down? What's the difference between the RST and FW_RST?

There is no need for a pull-up/pull-down and it works fine without a resistor, too, though, if you wanna be extra-careful you could slap a 1kOhm one on each. Also, FW_RST is active when pulled HIGH, not LOW, so whatever button you connect has to go to 3.3V instead.

The difference between the two is that RST just simply reboots the hardware, whereas FW_RST is for resetting the firmware to default-settings.

Is it okay to leave the unused pins hanging? What are the minimum connections?

Yes. Two -- 3.3V and GND.

What's the purpose of VOUT? Should I connect this to my 3.3v supply?

It's related to the ethernet-port, but I don't really know much else. Can just be left hanging.

It looks like SPI is driven by software on any GPIO port. Is it safe to repurpose ANY green GPIO port for SPI? What speeds are supported for SPI?

There is a hardware SPI-bus, too.

Ken Conrad

@Robert-Bouillon Have you seen Charle Hallard's work on Omega shields? His Eagle files may be helpful to you.

Robert Bouillon

Thanks for the replies-

@WereCatf - So FW_RST is active HIGH and RST is active LOW?

@Ken-Conrad - Thanks, I'll check those out.

ccs hello

Robert,
See https://community.onion.io/topic/1524/would-someone-clarify-the-exact-function-of-these-omega2-pins

Nominal operations current: 180mA.
Peak: 280mA.
The worst transit/inrush I saw is from 110mA jumps to 280mA. This is what many had reported: Omega2 won't boot, and current drops down to 60 mA. <-- system brown out

ccs_hello

Robert Bouillon

Okay so I'm thinking 500mA to be safe, then. Any word on hibernate functionality?

WereCatf

@Robert-Bouillon The SoC doesn't offer anything like that, it has zero power-management features.

Robert Bouillon

I found the datasheet here, in case it helps anyone else.

http://labs.mediatek.com/fileMedia/download/9ef51e98-49b1-489a-b27e-391bac9f7bf3

It does look like the SoC has support for a system sleep option.

But it looks like this datasheet should give me the information I need to work with the Omega 2 effectively.

György Farkas

@Robert-Bouillon
Footnotes

Although the "current" word is known to MediaTek, many details are missing:

current consumption(s)
GPIOs IOL, IOH absolute maximum / characteristic(s)

And an official Omega2/2+ schematic would be nice for an effective work.