The Teensy 3.x/4.x Series by PJRC are next generation ARM-based microcontrollers. They have loads of RAM, a faster clock speed and a host of add-ons.
It’s teensy because it is even smaller than a Nano, but it is even more powerful than a Nano Every. This is not an Arduino, it is from a company called PJRC. Since they use different processors, there are a lot of changes in the software that load onto the teensy when you select that as your processor.
There are several versions 3.2, 3.5, 3.6, 4.0, 4.1. with the biggest difference being the size/number of pins. You can also purchase the boards with or without the headers soldered on.
The above is a Teensy 3.2 compared to a quarter. Below is a Teensy 3.6 if you need more GPIO pins
There are even expansion boards to add WiFi and Ethernet. There is a Mega form factor board available to allow you to use 3.3V shields.
Teensy 3.6 Specifications
180 MHz ARM Cortex-M4 with Floating Point Unit
1M Flash, 256K RAM, 4K EEPROM
Microcontroller Chip MK66FX1M0VMD18
USB High Speed (480 Mbit/sec) Port
2 CAN Bus Ports
32 General Purpose DMA Channels
22 PWM Outputs
4 I2C Ports
11 Touch Sensing Inputs
62 I/O Pins (42 breadboard friendly)
25 Analog Inputs to 2 ADCs with 13 bits resolution
2 Analog Outputs (DACs) with 12 bit resolution
22 PWM Outputs
USB Full Speed (12 Mbit/sec)
Port Ethernet mac, capable of full 100 Mbit/sec speed
Native (4 bit SDIO)
micro SD card port
I2S Audio Port
4 Channel Digital Audio Input & Output
19 Hardware Timers
Cryptographic Acceleration Unit
Random Number Generator
CRC Computation Unit
6 Serial Ports (2 with FIFO & Fast Baud Rates)
3 SPI Ports (1 with FIFO)
Real Time Clock
EX‑CommandStation will run on all these boards, however the following caveats apply:
Teensys are strictly 3.3V, so you have to be careful that anything connected to the GPIO ports is also 3.3V (see also other 3.3v microcontrollers)
Teensy 3.x models are all now considered “legacy” products by PCJR and marked “Not recommended for new designs or projects”, with only Teensy 4.0/4.1 recommended by PCJR
Version 3.1, development versions 4.2.4 and beyond, and upcoming 5.x releases of EX‑CommandStation can compile for the Teensy models listed above, but have not been extensively tested
Teensy I2C peripheral uses the blocking Arduino Wire library, as there is no DCC-EX native non-blocking I2C driver for any of the Teensy range presently available, or planned. This will limit performance somewhat when using I2C peripherals attached to your Teensy.
Note that no further development and testing efforts by the core development team will be directed to Teensy models under the current roadmap
The major downside to all Teensy models is that PJRC is a very small company so as such it simply doesn’t have the resources or the staff of major manufacturers like Arduino, Espressif or ST Microelectronics.