Hi, I've recently written an introductory textbook based on the FRDM-KL25Z:
Embedded Systems Fundamentals with ARM Cortex-M based Microcontrollers: A Practical Approach, Alexander G. Dean, ARM Education Media, 1st Edition, 2017 ISBN: 978-1-911531-03-6 (print), 978-1-911531-01-2 (eText)
I use the book to support my embedded systems classes at NC State University. The book goes hands-on early, with blinking LEDs and reading switches in Chapter 2. Concurrency is critical for embedded systems, so Chapter 3 looks at scheduling concepts, introducing FSMs, polling, prioritization, preemption, and hardware peripherals. The book also covers essentials such as peripherals (including watchdog timers and DMA), the ARM Cortex-M0+ core, interrupts, the software development toolchain, software structures, and power analysis/reduction on the FRDM-KL25Z.
You can find book details at Embedded Systems Fundamentals with ARM Cortex-M based Microcontrollers: A Practical Approach | Embedded Dean
The book supports the efficient embedded system development course material I've developed for ARM's university program.
Thanks for any feedback!