PXD20RM Datasheet, PDF (561/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

indicating that the pixels displayed did not match what was expected. The signature calculator then
continues to calculate the CRC for the next frame. If the CRC_READY flag is not processed within one
frame time period, then the CRC_OVERFLOW interrupt is issued and the latest calculation overwrites the
previous value. Since the CRC_READY flag is set at the end of any frame with Safety Mode enabled, it
is possible that a full frame has not yet been completed and therefore no signature calculation exists for
the frame that set the flag.
If the user has set the NEG bit for the DCULite, which indicates that the pixels fed to the display are
inverted, then the value CRC is calculated on non-inverted values. The position CRC, however, remains
as is.
Normal arbitration takes place only when a pixel has content on layer 0 and layer 1 but where safety mode
is enabled in layer 1.
The polynomial used for CRC calculation is
(x³² + x²⁶ + x²³ + x²² + x¹⁶ + x¹² + x¹¹ + x¹⁰ + x⁸ + x⁷ + x⁵ + x⁴ + x² + x + 1)
Eqn. 12-5
For the value CRC, the 24-bit value of each output pixel (after decoding) is sent to the polynomial. For the
position CRC, the value sent is
(pixel_delta_y * display.delta_x) + (pixel_delta_x + 1)
Eqn. 12-6
Normal Mode Operation
1-32 bpp
FGPlane
Format ^{24 bpp Blending 24 bpp} _Gamma
1-32 bpp ^Converter
/Chroma
Key
Correc.
24 bpp
Display ^{24 bpp}
Drive
BGPlane
Display
Safety Mode
FGPlane
BGPlane
1-24 bpp
1-24
bpp
Format
Converter
25
bpp
optional
Chroma
Key
25 bpp ^optional
Gamma
Correction
25 bpp
Display
Drive
24 bpp
25 bpp = 24 bpp RGB + 1 bit safety pixel tag _Result
Interrupt
sync tag
Signature
Calculator
Figure 12-84. Safety Mode block diagram
Display
optional
external
signature
calculator
checker
Freescale Semiconductor
PXD20 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
12-99