Most CPUs have instructions like LOCK, LDREX/STREX, etc which
allows for atomic operations without locking interrupts that
can be invoked from user mode without complication. They typically
use compiler builtin atomic operations, or custom assembly
to implement them.
However, some CPUs may lack these kinds of instructions, such
as Cortex-M0 or some ARC. They use these C-based atomic
operation implementations instead. Unfortunately these require
grabbing a spinlock to ensure proper concurrency with other
threads and ISRs. Hence, they will trigger an exception when
called from user mode.
For these platforms, which support user mode but not atomic
operation instructions, the atomic API has been exposed as
system calls.
Some of the implementations in atomic_c.c which can be instead
expressed in terms of other atomic operations have been removed.
The kernel test of atomic operations now runs in user mode to
prove that this works.
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
Mostly useless patch. All architectures have their own code for
atomic operations and don't use this fallback. Still, it's a trivial
locking setup and we might as well.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
Replace the existing Apache 2.0 boilerplate header with an SPDX tag
throughout the zephyr code tree. This patch was generated via a
script run over the master branch.
Also updated doc/porting/application.rst that had a dependency on
line numbers in a literal include.
Manually updated subsys/logging/sys_log.c that had a malformed
header in the original file. Also cleanup several cases that already
had a SPDX tag and we either got a duplicate or missed updating.
Jira: ZEP-1457
Change-Id: I6131a1d4ee0e58f5b938300c2d2fc77d2e69572c
Signed-off-by: David B. Kinder <david.b.kinder@intel.com>
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
Also remove mentions of unified kernel in various places in the kernel,
samples and documentation.
Change-Id: Ice43bc73badbe7e14bae40fd6f2a302f6528a77d
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
