PXD20RM Datasheet, PDF (443/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

If a write is made to a register whose SLB is set then a transfer error occurs that generates an IVOR1
exception on the CPU. Similarly if the HLB is set then any write to the SLB registers causes a transfer
error.
11.6.2 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 & Transparency Registers for Layer1
• DISP_SIZE
• HSYNC_PARA
• VSYNC_PARA
• SYN_POL
11.7 Safety Mode
Safety layers are used in a multi-layer DCU3 environment for the purpose of guaranteeing that the content
is driven to the display regardless of the setting of remaining layers and the pixel manipulation algorithms
of the DCU3. Features such as this are a requirement from qualification institutes to be able to reach a
safety level of SIL2 or ASILB. The DCU3 has two safety layers (Layer 0 and Layer 1) which also have
the highest priority. When Safety Mode is active the safety layers can use chroma keying for complex area
description, however alpha blending for the layer is always ignored. Additionally, if a layer has safety
mode enabled then a layer format of 32 bpp or luminance is not allowed. Using these formats causes the
layer to be disabled.
Safety Mode is implemented using a signature calculator module implemented inside the DCU3 that
calculates two signatures (pixel value and pixel position) for a predefined area of the frame. The user
makes layer 0 and/or layer 1 active as a safety layer, defines the window/area of the pixels for which the
signature is to be calculated, and enables safety mode. When enabled, the signature calculator starts to
calculate the signature after the first pixel in the selected area is available and after the start of the next
frame (VSYNC). It is also possible to calculate the signature value for all pixels if
DCU_MODE[TAG_EN] = 0.
As the pixels in the selected area become available they are "tagged" by the DCU3, except for those
removed by chroma-keying. These tags identify the pixels to be included in the signature calculation. The
signature calculation itself is an industry-standard CRC.
The DCU3 asserts the CRC_READY flag at the end of any frame which has Safety Mode enabled. This
can be used to indicate the completed signature calculations for each full frame of pixels after the mode is
enabled. The completed signature can then be compared against a pre-calculated value with any difference
Freescale Semiconductor
PXD20 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
11-109