Display Control Unit (DCU)
MPC5606S Microcontroller Reference Manual, Rev. 7
432 Freescale Semiconductor
12.6.2 List of protected registers
The register protection scheme applies to the following registers:
• All Layer 0 control descriptors CTRLDESCL0_1 to CTRLDESCL0_7
• All Layer 1 control descriptors CTRLDESCL1_1 to CTRLDESCL1_7
• Layer 0 foreground and background registers for transparency mode FG0_FCOLOR and
FG0_BCOLOR
• Layer 1 foreground and background registers for transparency mode FG1_FCOLOR and
FG1_BCOLOR
• all Control Descriptors and Transparency Registers for Layer1
• DISP_SIZE
• HSYNC_PARA
• VSYNC_PARA
• SYN_POL
12.7 Safety mode
Safety layers are used in a multi-layer DCU environment for the purpose of guaranteeing that the content
is visible on the display regardless of the setting of remaining layers and the pixel manipulation algorithms
of the DCU.Safety Feature is a requirement from qualification institutes to be able to reach a safety level
of SIL2 or ASILB.The safety layers (Layer 0 and Layer 1) have the highest priority and use chroma key
for complex area description.When a layer has safety mode enabled and layer format is 32 bpp or
luminance mode, the layer is disabled as this is a wrong setting.Also alpha blending for the layer is
disabled if layer has safety mode enabled.
A signature calculator module is implemented in the DCU that calculates the signature (value and position)
for a predefined area of the frame.
DCU specifies a set of registers which define the window/area of the pixels for which CRC needs to be
calculated. The application sets these registers. The signature calculator starts to calculate the signature
after the first vertical (frame) sync after activation and when first pixel in the selected area is activeness
tagged). It is also possible to calculate the CRC value for all pixels if the TAG_EN bit in the register is set
to 0.
The pixels in the region of the layer on which signature needs to be calculated are tagged by the DCU. All
the pixels for the safety layer enabled layer are tagged and then depending on the chroma keying operation,
pixels with tagged values are passed along with the original data (24 bpp RGB + 1 bit safety pixel tag).
The CRC value for these tagged pixels are then calculated by the Signature calculator.
Once CRC calculation is done on all the pixels in the window of interest, an interrupt CRC_Ready is
generated for the processor to compare the CRC value with a precomputed value. Signature calculator
would continue to calculate CRC for the next frame. If the interrupt is not processed within one frame time
period, then CRC overflow interrupt is issued. The signature calculator calculates the content signature and
position signature.
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