The order that the HDMI core presents chroma samples differs from the Avalon-ST expectations for YCbCr 4:4:4 and 4:2:2 sampling schemes.
For YCbCr 4:4:4, it is necessary to perform the translation shown in the figure below to meet the Avalon-ST requirements. If the system only handles YCbCr, then you can use the Color Plane Sequencer II IP core to perform this remapping. If the system handles both RGB and YCbCr, then you need to use the Color Space Converter II IP core to convert between RGB and YCbCr and also to remap the color plane ordering for YCbCr 4:4:4.
YCbCr 4:2:2 require two potential remappings. Symbols 2 and 1 carry the upper 8 bits of the chroma and luma samples. If the system supports 10- or 12-bit depth, the additional bits are carried together in symbol 0. To support 10 or 12 bit, YCbCr 4:2:2 requires the recombining of these lower bits with the upper bits in 2 distinct symbols as shown in the figure below.
At present, a Mux instantiated between the HDMI IP core and the clocked video IP core implements the recombining of the 4:2:2 MSBs with LSBs. Future clocked video IP cores will support this remapping internally.
Note: For 8-bit inputs, recombination is not necessary.
The positioning of the luma and chroma in the upper 2 symbols is at odds with the Avalon-ST requirement for the chroma in the bottom symbol and luma in the symbol above. The luma samples are in the correct place but the chroma samples must be remapped from the upper symbol to lower symbol.
If the system only handles YCbCr, then you can use the Color Plane Sequencer II IP core to remap the symbols. If the system handles both RGB and YCbCr, then you need to use the Color Space Converter II IP core to remap the chroma samples.