Close IRQ in context switch to avoid abnormal sampling result

This abnormal sampling results from context switch processing in PendSV
being preempted by ktimer IRQ which triggers sampling event periodically.

Fixes #40

Signed-off-by: Jim Huang <jserv@0xlab.org>
save lr in each context switch and only compare last 4bits in lr

EXC_RETURN[4] in normal context differs from that in FPU context
Support FPU context handling.

Fixes #9

While context switching, FPU registers saving and restoring are
supported, and EXC_RETURN[4] in lr is used for identifying FPU context
and save/restore FPU registers if needed.
migrate namespace to queue rather than generic fifo

Fixes 44

Use explicit queue for implementation consistency
mk: unify the usage of  "chip" and "platform" for consistency

Fixes #21
platform: syntax tweaks
systick: reload need to be one less than heartbeat
tickless-verify shwo counts of tickless entering
tickless-verify: add a function to save current ticks
add compensation for systick when tickless enable
compensation for systick when tickless sleep interrupted
Show tickless compensation suggestion
mk: tickless-verify depends on tickless kernel
ktimer: make tickless-compensation configurable
config: move kernel configuration to independent file

Move to kernel/Kconfig

Signed-off-by: Viller Hsiao <villerhsiao@gmail.com>
introduce initialization hooks

Close #30
config: centralize development configuration

Signed-off-by: Viller Hsiao <villerhsiao@gmail.com>
kernel: get rid of redundant prefix f9 in init-hook
config: move options to config system

Move DEBUG, CONFIG_DEBUG, CONFIG_KDB to kernel/Kconfig

Signed-off-by: Viller Hsiao <villerhsiao@gmail.com>
kernel: unify the consistent naming, init_hook