RTOS for safety-critical systems has IEC 61508 certification
Documentation package speeds safety certification process for end-equipment
EDN Europe, 26 Apr 2007
26th April 2007 – A version of the
operating system is now available certified to comply with IEC 61508.
SafeRTOS is a small-footprint real-time kernel that achieves the
standard’s safety and integrity level 3 (SIL3). Certification was
carried out by TUV SUD. SafeRTOS is a portable, mini, pre-emptive
real-time kernel, predominantly written in C, with no restriction on
the number of tasks or priorities that you can use. It uses queues and
semaphores for communication and synchronisation between tasks, or
between tasks and interrupts. SafeRTOS was written, as was the FreeRTOS
code, by Richard Barry, head of innovation at ,
using ISO9001:2000 procedures cross-referenced to an IEC61508
compliance matrix. This, the company says, provides a full
certification package that speeds the user’s route to certification of
an end-product into which the software is built. 61508 categorises
safety-related systems according to their SIL, level 4 beign the
highest: level 3 is the highest obtainable for software-only components.
FreeRTOS
is a portable, open-source kernel that is free to download and is
royalty-free. Barry has ported it to 13 small-to-medium processor
cores, mostly 32-bit devices but with some 16- and 8-bit types. Users
have also carried out “unofficial” ports to further cores. Now,
Wittenstein has introduced OpenRTOS, which is essentially FreeRTOS that
is provided under a paid-for licence that brings with it supports, and
also frees the user from the restrictions of the General Public Licence
that governs use of the free version. The Safe version of the product
is available on a more limited selection of cores, but the company says
that further ports and compiler version can be added quickly.
The
product reduces development times by providing an out-of-the-box
scheduler, and provides pre-emptive, co-operative and hybrid
configurations. Barry prefers to give a level of detail in specifying
how much memory the software takes up; for example, he says that when
running on an ARM7, with full optimisation and including all components
other than co-routines and trace functions, the core scheduler will
occupy 236 bytes of RAM; each queue that you add adds 76 bytes and
associated queue storage area; and each task you created adds 64 bytes
plus the stack size for that task. The kernel itself resides in under 4
kbytes of ROM.
OpenRTOS licences start at under $1000: you can buy
the SafeRTOS kernel without the full certification package, at around
$4000, and adding the full certification documentation takes this to
around $20,000.
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