Content tagged frdm-k64f

Board bring-up

I started playing with the FRDM-K64F board recently. I want to use it as a base for a bunch of hobby projects. The start-up code is not that different from the one for Tiva, which I describe here - it's the same Cortex-M4 architecture after all. Two additional things need to be taken care of, though: flash security and the COP watchdog.

The K64F MCU restricts external access to a bunch of resources by default. It's a great feature if you want to ship a product, but it makes debugging impossible. The Flash Configuration Field (see section 29.3.1 of the datasheet) defines the default security and boot settings.

 1 static const struct {
 2   uint8_t backdor_key[8];   // backdor key
 3   uint8_t fprot[4];         // program flash protection (FPROT{0-3})
 4   uint8_t fsec;             // flash security (FSEC)
 5   uint8_t fopt;             // flash nonvolatile option (FOPT)
 6   uint8_t feprot;           // EEPROM protection (FEPROT)
 7   uint8_t fdprot;           // data flash protection (FDPROT)
 8 } fcf  __attribute__ ((section (".fcf"))) = {
 9   {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
10   {0xff, 0xff, 0xff, 0xff}, // disable flash program protection
11   0x02,                     // disable flash security
12   0x01,                     // disable low-power boot (section 6.3.3)
13   0x00,
14   0x00
15 };

If flash protection (the fprot field) is not disabled, you won't be able to flash new code by copying it to the MBED partition and will have to run mass erase from OpenOCD every time:

interface cmsis-dap
set CHIPNAME k60
source [find target/kx.cfg]
kinetis mdm mass_erase

If the MCU is in the secured state (the fsec field), the debugger will have no access to memory.

The structure listed above needs to end up in flash just after the interrupt vector. I use the linker script to make sure it happens. I define the appropriate memory block:

FLASH-FCF  (rx)  : ORIGIN = 0x00000400, LENGTH = 0x00000010

And then put the .fcf section in it:

.fcf :

See here.

I also disable the COP (computer operates properly) watchdog which resets the MCU if it is not serviced often enough.

1 WDOG_UNLOCK = 0xc520;        // unlock magic #1
2 WDOG_UNLOCK = 0xd928;        // unlock magic #2
3 for(int i = 0; i < 2; ++i);  // delay a couple of cycles
4 WDOG_STCTRLH &= ~0x0001;     // disable the watchdog

You can get the template code at GitHub.


My medium-term goal is to port my Silly Invaders game to a Real Time Operating System. Zephyr seems to be a good choice. It's open source, operates under the auspices of the Linux Foundation and has an active community with many developers from Intel committing the code.

They, unfortunately, do not support Tiva so I will need to port the OS before I can proceed with the application. I decided to buy the Freescale K64F board, which is supported, to familiarize myself a little with Zephyr before I start the porting work. The howto page for setting up K64F seems to be terribly complicated and requires a JTAG programmer. I summarize here a simpler way using cmsis-dap over USB.


I updated the MBED interface firmware following the instructions on this site. I also build my own OpenOCD from the head of the master branch using the following configuration options:

./configure --prefix=/home/ljanyst/Apps/openocd  --enable-cmsis-dap

Things may work fine with the stock firmware and the stock OpenOCD as well, but I did not try that. It's also probably a good idea to add the following udev rule so that you don't have to run things as root:

]==> cat /etc/udev/rules.d/99-openocd.rules
# frdm-k64f
ATTRS{idVendor}=="0d28", ATTRS{idProduct}=="0204", GROUP="plugdev", MODE="0660"
]==> sudo udevadm control --reload-rules

Hello world!

I use the ARM cross-compiler provided by Debian to compile Zephyr and then just copy the resulting binary to the MBED disk:

]==> cd samples/hello_world/nanokernel
]==> make BOARD=frdm_k64f CROSS_COMPILE=arm-none-eabi- CFLAGS=-O0
]==> cp outdir/zephyr.bin /media/ljanyst/MBED/

You can see the effects in the UART console using screen:

]==> screen /dev/ttyACM0 115200,cs8
Hello World!

I then run OpenOCD using the following script:

]==> cat k64f.cfg
set CHIPNAME k60
source [find target/kx.cfg]

$_TARGETNAME configure -event gdb-attach {

]==> openocd -s /home/ljanyst/Apps/openocd/share/openocd/scripts/ -c "interface cmsis-dap" -f k64f.cfg

And GDB:

]==> cat remote1.conf
target extended-remote :3333
monitor reset init
break main
]==> arm-none-eabi-gdb  --command=remote1.conf outdir/zephyr.elf
Breakpoint 1 at 0x129c: file /home/ljanyst/Projects/zephyr/zephyr-project/samples/hello_world/nanokernel/src/main.c, line 37.
Note: automatically using hardware breakpoints for read-only addresses.

Breakpoint 1, main () at /home/ljanyst/Projects/zephyr/zephyr-project/samples/hello_world/nanokernel/src/main.c:37
37              PRINT("Hello World!\n");
(gdb) s
printk (fmt=0x2c90 "Hello World!\n") at /home/ljanyst/Projects/zephyr/zephyr-project/misc/printk.c:164
164             va_start(ap, fmt);
(gdb) s
165             _vprintk(fmt, ap);
(gdb) s
_vprintk (fmt=0x2c90 "Hello World!\n", ap=...) at /home/ljanyst/Projects/zephyr/zephyr-project/misc/printk.c:75
75              int might_format = 0; /* 1 if encountered a '%' */
(gdb) where
#0  _vprintk (fmt=0x2c90 "Hello World!\n", ap=...) at /home/ljanyst/Projects/zephyr/zephyr-project/misc/printk.c:75
#1  0x00001b46 in printk (fmt=0x2c90 "Hello World!\n") at /home/ljanyst/Projects/zephyr/zephyr-project/misc/printk.c:165
#2  0x000012a2 in main () at /home/ljanyst/Projects/zephyr/zephyr-project/samples/hello_world/nanokernel/src/main.c:37