teensy-3.x

Tags: arch:arm chip:kinetis vendor:nxp

The Teensy 3.1 and 3.2 are compact, breadboard-friendly development boards designed by PJRC (Paul Stoffregen), powered by the NXP (formerly Freescale) Kinetis MK20DX256VLH7 ARM Cortex-M4 microcontroller.

This board configuration also supports the earlier Teensy 3.0 board (which features the Kinetis MK20DX128VLH5 microcontroller).

Note

The initial port of NuttX to the Teensy 3.1 was contributed by Jakob Odersky (jodersky).

Hardware Overview

Comparison: Teensy 3.0 vs. Teensy 3.1 / 3.2

The Teensy 3.1 and 3.2 share identical pinouts and schematics with the Teensy 3.0, but feature a significantly enhanced MCU:

Feature

Teensy 3.0

Teensy 3.1 / 3.2

Teensy 3.0 Configuration

Processor

NXP MK20DX128VLH5

NXP MK20DX256VLH7

CONFIG_ARCH_CHIP_MK20DX128VLH5=y

Core

ARM Cortex-M4

ARM Cortex-M4

ARM Cortex-M4

Rated Clock

48 MHz

72 MHz

Selected via board clock header

Overclockable

Up to 96 MHz

Up to 96 MHz

CONFIG_TEENSY_3X_OVERCLOCK=y

Flash Memory

128 KB

256 KB

Selected via linker script

SRAM

16 KB

64 KB

CONFIG_RAM_SIZE=16384

5V Tolerance

No (3.3V only)

Yes (Digital pins)

No (3.3V only)

Linker Script

mk20dx128vlh5.ld

mk20dx256vlh7.ld

Automatic based on chip selection

Warning

While digital I/O pins on the Teensy 3.1/3.2 are 5V tolerant, the analog inputs (A10, A11, AREF, and the internal ADC reference) are strictly 3.3V maximum. On the Teensy 3.0, all pins are 3.3V only. Exceeding 3.3V on non-tolerant pins will permanently damage the microcontroller.

Key Features (Teensy 3.1 / 3.2)

  • Microcontroller: NXP Kinetis MK20DX256VLH7 (64-pin LQFP) - 32-bit ARM Cortex-M4 running at 72 MHz (overclockable up to 96 MHz) - 256 KB Flash memory, 64 KB SRAM - Hardware CRC and Random Number Generator

  • Clocking: - 16 MHz external crystal (XTAL on PTA18/PTA19) - On-chip PLL generating 72 MHz system clock (or 96 MHz when overclocked)

  • USB Interface: - Full-Speed (12 Mbps) USB 2.0 Device/Host/OTG port with Micro-B connector - Dedicated USB regulator providing 3.3V (up to 100 mA) to external circuits

  • Serial Communication: - 3 UARTs with FIFO and hardware CTS/RTS support - 2 SPI modules with FIFO - 2 I2C modules with SMBus support

  • Analog & Timers: - 2 16-bit ADCs with differential mode support - 1 12-bit DAC - 3 FlexTimer modules (FTM) supporting up to 12 PWM channels - Carrier Modulator Transmitter (CMT) - Real-Time Clock (RTC) with external 32.768 kHz crystal footprint

  • Form Factor & Bootloader: - 24-pin DIP footprint (0.1” pitch, breadboard friendly) - Onboard Nuvoton Mini54TAN processor running PJRC HalfKay USB bootloader - Pushbutton for entering bootloader mode

Pin Configuration

Nearly all MCU port pins are routed to the outer header pins or underside pads. The dedicated onboard hardware connections are:

Port Pin

Board Usage

PTA0

Mini54TAN / Bootloader communication

PTA1

Mini54TAN / Bootloader communication

PTA2

Mini54TAN / Bootloader communication

PTA3

Mini54TAN / Bootloader communication

PTA18

16 MHz Crystal (XTAL)

PTA19

16 MHz Crystal (XTAL)

PTB1

Mini54TAN / Bootloader communication

PTB2

Mini54TAN / Bootloader communication

PTC5

User LED (Orange)

Serial Console

The Kinetis K20 provides three UART modules with pins exposed on the board headers:

UART Module

Port Pin

Board Label

PJRC Pinout Description

UART0_RX

PTB16

Pin 0

RX1 / Touch

PTD6

Pin 21 / A7

RX1 / CS / PWM

PTA1

(Internal)

Mini54TAN / Bootloader

UART0_TX

PTB17

Pin 1

TX1 / Touch

PTD7

Pin 5

TX1 / PWM

PTA2

(Internal)

Mini54TAN / Bootloader

UART1_RX

PTC3

Pin 9

RX2 / CS / PWM

PTE1

Pad 26

Pad on underside of board

UART1_TX

PTC4

Pin 10

TX2 / CS / PWM

PTE0

Pad 31

Pad on underside of board

UART2_RX

PTD2

Pin 7

RX3 / DOUT

UART2_TX

PTD3

Pin 8

TX3 / DIN

The default serial console in the nsh configuration is UART0 on:

  • RX: Pin 0 (PTB16)

  • TX: Pin 1 (PTB17)

  • Baud rate: 115200 8N1

Connect a 3.3V USB-to-UART serial adapter (TX to Pin 0, RX to Pin 1, GND to GND) to access the NuttShell prompt.

LEDs

A single orange LED is connected to port pin PTC5. The cathode is connected to ground, so driving PTC5 high illuminates the LED.

When CONFIG_ARCH_LEDS is enabled, NuttX indicates system status as follows:

Symbol

Meaning

LED

LED_STARTED

NuttX has started

OFF

LED_HEAPALLOCATE

Heap has been allocated

OFF

LED_IRQSENABLED

Interrupts enabled

OFF

LED_STACKCREATED

Idle stack created

ON

LED_INIRQ

Handling an interrupt

No Change

LED_SIGNAL

Inside signal handler

No Change

LED_ASSERTION

Assertion failed

No Change

LED_PANIC

System has crashed

Flashing (2 Hz)

When NuttX boots successfully and enters normal idle operation, the LED remains solidly ON. If a kernel panic occurs, the LED flashes at approximately 2 Hz.

Flashing and Debugging

Using the Teensy Loader

The Teensy 3.x comes pre-programmed with PJRC’s proprietary HalfKay bootloader managed by the onboard Mini54TAN chip. The bootloader communicates over USB via the Teensy Loader application or the command-line tool teensy_loader_cli.

NuttX configurations for the Teensy 3.x enable Intel HEX binary generation (CONFIG_INTELHEX_BINARY=y), which produces nuttx.hex in the root directory after compilation.

Flashing with teensy_loader_cli:

  1. Install teensy_loader_cli on your host system:

    # Ubuntu / Debian
sudo apt-get install libusb-dev
git clone https://github.com/PaulStoffregen/teensy_loader_cli.git
cd teensy_loader_cli && make && sudo make install

  2. Build NuttX and upload the generated nuttx.hex:

    # For Teensy 3.1 / 3.2 (MK20DX256):
teensy_loader_cli --mcu=mk20dx256 -w -v nuttx.hex

# For Teensy 3.0 (MK20DX128):
teensy_loader_cli --mcu=mk20dx128 -w -v nuttx.hex

  3. Press the pushbutton on the Teensy 3.x board to initiate the programming cycle. Once flashing completes, the board reboots into NuttX automatically.

Hardware Debugging (SWD / JTAG)

Standard hardware debugging via SWD is not directly available out of the box because the onboard Mini54TAN bootloader chip controls the Reset and SWD lines of the K20 microcontroller.

To use an external SWD debugger (such as J-Link, ST-Link, or CMSIS-DAP), the hardware traces between the Mini54TAN and the MK20 chip must be severed or the Mini54TAN held in permanent reset. For detailed instructions on this modification, refer to the Hacking the Teensy 3.1 for SWD Debugging guide on MCU on Eclipse.

Supported Configurations

The board configurations for the Teensy 3.x are located under boards/arm/kinetis/teensy-3.x/configs/.

nsh

The default NuttShell (NSH) configuration provides an interactive command-line interface over the primary serial port.

  • Console: UART0 (Pin 0 RX, Pin 1 TX) at 115200 8N1

  • Binary formats: Raw binary (nuttx.bin) and Intel HEX (nuttx.hex)

  • Builtin applications: Enabled

Building:

./tools/configure.sh teensy-3.x:nsh
make -j$(nproc)
teensy_loader_cli --mcu=mk20dx256 -w -v nuttx.hex  # Use --mcu=mk20dx128 for Teensy 3.0

usbnsh

Configures the NuttShell console to run over the native USB port using the USB CDC/ACM class driver (virtual COM port).

  • Console: USB CDC/ACM (/dev/ttyACM0 on Linux, COMx on Windows)

  • Driver: Kinetis Full-Speed USB Device controller (CONFIG_KINETIS_USBOTG=y)

  • Hardware requirement: Standard Micro-USB cable connected directly to the host PC

Building:

./tools/configure.sh teensy-3.x:usbnsh
make -j$(nproc)
teensy_loader_cli --mcu=mk20dx256 -w -v nuttx.hex  # Use --mcu=mk20dx128 for Teensy 3.0

After flashing and rebooting, connect to the USB serial device:

# Linux
minicom -D /dev/ttyACM0

# Or using picocom
picocom -b 115200 /dev/ttyACM0