Do RAK2758 & RAK7249 use SPI or USB?

LPWAN Industrial Gateways / Concentrators RAK7249
1

I’m curious about how the LoRa concentrator card(s) and (optional) LTE modem in the RAK2758 & RAK7249 are connected to the MT7628 processor.

The MT7628 has one USB host port, a main SPI interface with one free automatic chip select, there is possibly a secondary SPI interface or a possibility to use a GPIO as a software chip select.

RAK2758 seems to ship with a single concentrator card, and have an exposed USB port, there’s a footprint for an LTE module not installed. My guess is that because of the exposed USB port the concentrator must be SPI. If you choose the LTE then you would lose the use of the USB port. Or else there is a USB hub chip?

  • SPI concentrator
  • USB jack
  • USB LTE (not installed, would prevent using the USB jack)

is that correct?

RAK2749 seems to support two concentrators and usually have an LTE modem, but does not appear to have a USB port.

  • SPI first concentrator
  • USB LTE

Is that correct?

If purchased with two concentrators, how does the second interface?

Or am I mistaken and these all use USB concentrator interface with a hub chip to share the processors USB between that and the LTE?

2

Got to examine a RAK2758 up close.

  • Can confirm the RAK2247 concentrator is the SPI version.

  • USB port works, continue to assume factory installed LTE would break that

  • SD card slot works, but system crashes if SD card installed/removed while running

3

Hello @cstratton
SD card is used for automatic data recovery. So when you plug/unplug the Gateway reboots not crashing.

4

Actually, if you connect a serial cable you will see that it is in fact an invalid operation in the kernel leading to a kernel panic, and then yes a reboot. And it occurs even when the sd card is properly unmounted before removal, and also on insertion. But it’s a software issue unrelated to LoRa functionality that is present across 3.18.45 (both the factory firmware and builds from your open source repos) and does not occur with Mediatek’s 3.18.44 kernel on the same hardware, so really a distinct topic from the question of this thread.

Are you able to comment on the interfaces used in the RAK7249? That’s key to understanding if the hardware will be suitable for our network.