In creating a functional Safety
Element out of Context (SEooC) concept and doing the functional safety analysis, TI
generates a series of assumptions on system level design, functional safety concept,
and requirements. These assumptions (sometimes called Assumptions of Use) are listed
below. Additional assumptions about the detailed implementation of safety mechanisms
are separately located in Section 6.4.
The
TMS320F28P65x Functional Safety Analysis was done under the following system
assumptions:
- [SA_1] The system
integrator shall follow all requirements in the component data sheet.
- [SA_2] The system shall be
configured to allow this device to activate or communicate with assigned
actuators to maintain proper operating state of the external system based on
input from assigned sensors.
- [SA_3] If the system is in
a fault detected state, software may attempt to recover from the fault before a
safety goal is violated. Software shall be configured to put the system into a
safe state, if unable to recover from a fault, before the violation of a safety
goal occurs.
- [SA_4] The system
integrator shall review the recommended diagnostics in the Safety Manual and
Safety Analysis Report (FMEDA), and determine the appropriate diagnostics to
include in their system. These diagnostics shall be implemented according to the
device Safety Manual and datasheet.
- [SA_5] The software shall
initialize the continuous diagnostics and periodically run the
test-for-diagnostics in alignment with the system safety concept including Fault
Tolerant Time Interval (FTTI), Process Safety Time (PST), and Multi-Point Fault
Detection Time Interval (MPFDTI).
- [SA_6] The power supply to
this device shall provide the appropriate power on each of the power inputs.
These rails shall be monitored for deviations outside the device
specifications.
- [SA_7] The power supply or
other external monitoring device(s) shall monitor the device error pins and
transition the system to a safe state after an unrecoverable error is
indicated.
- [SA_8] The power supply or
other external monitoring device shall monitor the device to provide coverage
for diagnosing power faults. A watchdog is an example technique to achieve this
diagnostic.
- [SA_9] The power supply or
other external monitoring device shall be used as a parallel path to disable
downstream actuators in situations such as before the device is capable to
perform a safety function (i.e. device startup) or when device faults have been
detected that would compromise the decision making capability of the device
(i.e. MCU fault conditions).
- [SA_10] A system concept
appropriate to the targeted ASIL/SIL level shall be chosen to detect faults in
the execution of the code running on the CPUs related to the safety function.
This concept shall also take into consideration shared modules (i.e. RAM, flash,
ADCs, etc.). Examples include, but are not limited to, reciprocal comparison by
software, watchdogs, etc.
- [SA_11] System
configuration and implementation checks shall be performed by the system
integrator.
- [SA_12] Availability of
system function is not a safety requirement. When the system is off or in reset,
it shall be in a safe state.
- [SA_13] Device power
sequencing requirements shall not be considered to be safety critical.
- [SA_14] The system
integrator shall review the SEooC analysis and integrate it into the system
level safety analysis, the diagnostics shall be applied as needed with respect
to the system safety goals and requirements, and integration testing shall be
performed.
- [SA_15] The system
integrator shall analyze the other components in the system with respect to the
safety concept and will implement diagnostics on those components as needed with
respect to that safety concept.
- [SA_16] The safety
function is considered to operate in high/continuous demand mode of operation
(per IEC 61508). (Note this does not exclude the option of operating in low
demand mode. This assumption is made to provide a baseline for judgment of the
Safety Integrity Level targets.)
- [SA_17] This device is
considered to be a type B safety-related element or subsystem (per IEC 61508).
Additionally, the F28P65x MCU claims no hardware fault tolerance (HFT = 0), as
defined in IEC 61508:2010.
- [SA_18] The safety
function shall not begin until the software enables it after this device has
successfully completed its startup sequence, run any required integrity checks,
and is in a normal mode of operation.
- [SA_19] Debug and Design
For Test (DFT) logic shall be disabled during operation of a safety
function.
During integration activities these
assumptions of use and integration guidelines described for this component shall be
considered. Use caution if one of the above functional safety assumptions on this
component cannot be met, as some identified gaps may be unresolvable at the system
level.