PXD20RM Datasheet, PDF (438/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

DMA
RXFIFO _RLE
decoder
TXFIFO
INPUT
FIFO
Figure 11-84. RLE Decoding in DCU3
The decoded data is read by the input FIFO once at least 8 bytes are available in the TXFIFO.The size of
RXFIFO is 64x8 bits while the size of TXFIFO is 16x8 bits.
If both layer 0 and layer 1 have RLE_EN set, then the error flag RLE_ERR is asserted.
11.4.10.1 RLE decoding scheme
Before enabling an RLE encoded layer configure the COMP_IMSIZE register with the size of the
compressed image. The decoder expects to read COMP_IMSIZE bytes from the image and produce from
that the number of pixels specified in the layer Control Descriptor 1 register.
The format of RLE encoded layers is as follows:
• The first data byte read at the image address (Layer Control Descriptor 3) is a command byte
(CMD[7:0])
• The ms bit (CMD[7]) indicates if the following bytes are raw or compressed pixels. One pixel can
be 8-bit, 16-bit, 24-bit or 32-bit wide, depending on the BPP bitfield in the Layer Control
Descriptor 4 register.
• The remaining 7 command bits (CMD[6:0]) specify the number of raw or compressed pixels that
follow the command byte. This count is offset by 1 such that a value of 0 means one pixel follows.
• For compressed pixels (CMD[7] = 1), only one pixel follows the command byte. This pixel is
repeated count+1 times on the layer. The pixel size may be 8, 16, 24 and 32 bits.
• For raw pixels (CMD[7] = 0) count+1 pixels follow the command byte and these are included on
the layer as is. The pixel size may be 8, 16, 24 and 32 bits.
• If there is more data to decode then a new command follows after CMD+(1*{Pixel width}) bytes.
This encoding is repeated until the whole image is decoded.
11.5 Timing, Error and Interrupt Management
The DCU3 can detect and raise status and error flags when the status of the system changes and when
configuration or operational errors are detected.
11-104
PXD20 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
Freescale Semiconductor