Erich of MCUonEclipse writes:
The Freescale FRDM boards are using a Kinetis K20 based circuit (see “OpenSDA on the Freedom KL25Z Board“): However, that firmware is not open: the K20 is secured and protected, so the firmware cannot be changed. Newer Freescale FRDM boards like FRDM-K22F2 and FRDM-K64F do have an open source bootloader and debug firmware (see “DOC-100720“).
So: take a Freescale Kinetis K20 ARM Cortex-M4, the open source bootloader and firmware, shrink everything to the size of a Teensy board, add headers both to debug the K20 and an off-board microcontroller, and we have tiny board which can be used as a standalone versatile microcontroller board: usable for small projects or usable as debug probe.
Features and wish list:
- Universal, tiny, breadboard friendly which can be used by students for their own projects and which can be used in courses and lab work.
- Freescale Kinetis K20 device, ARM Cortex M4, running up to 50 MHz, powerful enough for most tasks
- 128 KByte FLASH, 16 KByte RAM
- USB connector (both power and connectivity)
- Optional battery power
- Optional real time clock
- Reset/User button
- Breadboard friendly pin out, all pins available on the outside
- SWD debug interface to debug the onboard K20
- Ability to debug off-board devices with OpenSDAv2
- Small size, around 40×25 mm (TBD)
- Low cost (TBD, less than $<20, depends on quantity)
To prove the concept, we used the FRDM-K20D50M board, added buffers/level shifter and an inverter, hooked everything up to a SWD cable, loading the bootloader and debug firmware, and we are able to use it as a debug probe