If the data correctness check is enabled (see
Table 12-484, DISPC Safety Check Regions Parameters):
- When a new signature is generated, it is compared against
the reference signature provided by the software. A SAFETY_REF_SIGNATURE
register must be configured with a reference signature data, see Table 12-484, DISPC Safety Check Regions Parameters.
- If signatures do not match, an interrupt event is
generated to indicate data mismatch.
If the freeze frame detection is enabled (see
Table 12-484, DISPC Safety Check Regions Parameters):
- When a new signature is generated, it is first compared
against the saved signature (from previous frame).
- If signatures match, an internal counter used to keep
track of the number of frames with no data change (for the region) is
incremented.
- If signatures do not match, the counter is cleared.
- If the counter value is greater than the user programmed
freeze frame detection threshold value (see Table 12-484, DISPC Safety Check Regions Parameters), an interrupt event
(VIDSAFETYREGION_IRQ or VPSAFETYREGION_IRQ, see Section 12.9.1.4.1.5, DISPC Interrupt Requests) is generated to indicate a possible
freeze frame detection. The threshold value must be configured with the
maximum number of identical successive frames allowed before an interrupt is
generated.
- After the comparison, the signature is saved as the
previous signature.
- The counter is cleared when the interrupt event is
generated or when freeze frame detection check is disabled.
This frame freeze is different from the display frozen due to pipeline lock up. In that case, the DISPC will generate an SYNCLOST_IRQ and/or DMA VIDBUFFERUNDERFLOW_IRQ interrupt. The freeze frame detection is for source data frozen while the DSS is working normally.
The two safety checks are continuously performed over multiple frames as long as their mode enable register bits are set.