Add Silicognition RP2040-Shim

Add upcoming RP2040-Shim board (in production).

_board/silicognition-rp2040-shim.md

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+---
+layout: download
+board_id: "silicognition-rp2040-shim"
+title: "RP2040-Shim Download"
+name: "RP2040-Shim"
+manufacturer: "Silicognition LLC"
+board_url: "https://github.com/xorbit/RP2040-Shim"
+board_image: "silicognition-rp2040-shim.jpg"
+date_added: 2022-7-1
+family: raspberrypi
+features:
+  - Feather-Compatible
+  - Breadboard-Friendly
+---
+
+This board is an alternative to the [Silicognition M4-Shim](https://www.amazon.com/M4-Shim-Feather-PoE-FeatherWing-Ultra-Compact-Vertical/dp/B0971PKDV7/), and just like that board it is specifically made to fit on top of the [PoE-FeatherWing](https://www.amazon.com/Silicognition-PoE-FeatherWing-Ethernet-802-3at-Feather/dp/B08KTVD7BR/), filling the empty space around the RJ45 and flyback transformer and allowing the creation of extremely compact Power over Ethernet systems.
+
+Since the ATSAMD51J19 used on the M4-Shim is pretty much unobtainium right now, I needed to provide an alternative, and with good availability and popularity of the [RP2040](https://www.raspberrypi.com/products/rp2040/) this chip seemed like a natural choice.  You get dual ARM Cortex-M0+ @ 133 MHz, 264 kB on-chip SRAM, PIO and 4 MB of QSPI flash!
+
+The RP2040 comes with built-in UF2 bootloader, and the board has CircuitPython with Wiznet W5500 drivers pre-installed, plus a `poe_featherwing.py` module that sets the Ethernet connection up for you.
+
+A special feature of this board is a custom chip to enable the familiar single-press to reset, double-press for bootloader button!  So from a user experience point of view, it behaves the same as the M4-Shim.
+
+## Learn More
+* [Hardware Github repo](https://github.com/xorbit/RP2040-Shim)