There are so many processor board choices when considering the needs of a product or project. One decision point might be, do you choose a microcontroller or a more powerful single-board computer (SBC)? The new Teensy 4.1 from PJRC simplifies that decision because It combines the real-time nature of an Arduino-compatible microcontroller with the processing and I/O performance of an operating system-based SBC in a slim package.
Teensy 4.1 from PJRC is an update of their already mighty Arduino-compatible board. As the minor revision number suggests, the new board is an extension that builds on the previously introduced 4.0.
To clarify, while we call the Teensy 4.1 an upgrade or improvement to the Teensy 4.0, it is a standalone product. PJRC says this about their differences:
Not every project requires so much I/O or extra memory. Teensy 4.0 fills those needs. But when you do need more I/O, more memory, fast ethernet, or connecting USB devices or fast SD card access, the larger Teensy 4.1 brings this extra I/O capability to a platform designed for real-time use with fast 600 MHz M7 performance.
Both feature an NXP iMXRT1062 processor based on an Arm Cortex-M7 running at 600 MHz. On-board there is 1 MB RAM, 8 MB flash, and many I/O options. The larger size, now 61 mm x 17 mm, is the same as the Teensy 3.6. The additional size allows for more I/O pins and features new to the Teensy 4.1: 100 Mbit Ethernet, improved USB host, SD card socket, and memory expansions.
Of the improvements, adding 100 Mbit Ethernet support is likely the largest. There is a dedicated Ethernet physical layer interface (PHY). Combined with software on the iMX microcontroller, it supports the precision time protocol (PTP). Also known as IEEE 1588, this protocol allows for synchronizing connected devices with sub-microsecond precision.
Embedded microcontrollers communicating with Ethernet is not a new idea. The combination the Teensy 4.1 brings is a high-bandwidth, low latency 100 Mbit Ethernet connection without an add-on PCB (shield) or by moving to a full OS-based single board computer.
This capability means taking advantage of the real-time nature of the microcontroller and combining it with a high-throughput data pipe. Fast Ethernet has a raw bitrate of 125 Mb/s. After accounting for physical layer overhead, the maximum wire speed is 100 Mb/s. One beta user on the PJRC forums has successfully tested the link up to 95 Mb/s. Keep in mind, these are benchmarks with early software support, so speed in real applications my vary.
Since an Ethernet jack would not fit on the PCB, PJRC plans to sell a through-hole soldering kit to attach to the header pins. If you need to add a jack today, they have made a version of the adapter shown above, available at this Teensy 4.1 Ethernet OSH Park project link.
The previous Teensy 4.0 has pads to support a USB host connection. But, those surface mount pads are on the board's bottom, or back, side. (Third-party products like the Teensy expansion board gave an option to connect those pads to a physical port.)
With the new 4.1 version, there are through-hole pads and support for hot-plugging. Now you can add a physical port or a cable to plug directly into a device. For speed, the Teensy 4.1 USB port supports up to 480 Mbit per second.
SDIO is an extension of the SD specification that adds I/O capabilities. Teensy 4.1 replaces the 4.0's SDIO solder points with a microSD card socket. Now it is easy not only to access an SD card but also to use the high-speed SDIO interface.
While the new Teensy moved all of the 4.0's backside solder points to through-holes, it does not waste the space available on the larger form factor. The 4.1 has a couple of spots for user upgrades.
On the backside, there are two pads to solder additional memories. Remember that the Teensy 4.1 already comes with 1 MB of RAM and 8 MB of flash. One footprint lets you add a QSPI-based flash memory module. The Q in QSPI means quad, making it a fast serial interface. The iMXRT1062's architecture places it on a separate memory bus making it suitable for loading media files or save large data structures without stalling other processor activity.
A second footprint supports up to 8 MB of PSRAM. PSRAM is dynamic memory with a built-in refresh controller, so as a user, you can think of it as static RAM. Since this chip also gets accessed through QSPI, it would work well as large buffers for tasks like digital signal processing effects or TFT displays.
Starting today, you can order the Teensy 4.1 from PJRC. They sell for $26.85, which is only about $7 more than the 4.0. Visit the Teensy 4.1 product page at the PJRC store for more information.
Please note that information regarding Ethernet and PTP has been updated from the original article.The original article mistakenly said the PHY supports PTP. -James