Patch for clock.c: JN5139 does not have "vAHI_TickTimerRegisterCallback(...)" in AppHardwareApi.h. Added define "APP_HARDWARE_API_JN5148" (in /contiki-jn51xx/cpu/jennic/jn5148/AppHardwareApi.h) to use alternative implementation in clock.c to work around this.
Merge branch 'master' of https://github.com/rothenpieler/contiki-jn51xx
clock.c should work now as desired.