7.4.1 FIFO watermark
A watermark level is set such that the FIFO requests data via its DMA function
from the framebuffer when at least four locations in the FIFO become available.
The watermark level can be configured:
•
VOnLCDCONTROL.WATERMARK = 0: new data request if FIFO has
≥ 4 empty locations
•
VOnLCDCONTROL.WATERMARK = 1: new data request if FIFO has
≥ 8 empty locations
In case the FIFO is requested to output data while it is empty, i.e. an underflow
condition has occurred, the FIFO underflow interrupt VOnFUFINT is generated.
7.4.2 Framebuffer addressing
The first address of the first pixel data of the frame to be output, i.e. the
framebuffer base address, is defined by LCDUPBASE[31:0] in the register
VOnLCDUPBASE.
The content of VOnLCDUPBASE is copied to the current framebuffer address
register VOnLCDUPCURR at the timely start of each new frame output. During
output of the frame VOnLCDUPCURR is incremented, when the DMA function
reads new pixel data from the framebuffer.
If VOnLCDUPBASE has been copied to VOnLCDUPCURR, the LCD next base
address update interrupt VOnNBAINT is generated.
Note
The VOnLCDUPCURR value may change at any moment, and is not normally
read. It can be read to determine the approximate position within the framebuffer
or for test purposes.
In case the frame to be output to the display shall be changed, VOnLCDUPBASE
must be rewritten.
Since a new VOnLCDUPBASE address becomes effective always with the start
of a new frame, it must be ensured, that the previous VOnLCDUPBASE address
is effectively in use prior rewriting VOnLCDUPBASE. Therefore wait for the LCD
next base address update interrupt VOnNBAINT, which indicates, that the
previous VOnLCDUPBASE is effective and can be overwritten.
VOnLCDUPBASE denotes a byte address, thus the two LSBs LCDUPBASE[1:0]
must be 00
B
due to 32-bit word memory.
Caution
The LCD next base address update interrupt VOnNBAINT is generated at the
beginning of each frame, independent of whether a new address was written to
VOnLCDUPBASE.
7.5 Interrupts
The Video Output module generates four raw interrupts and additionally a
common interrupt.
A set of registers are used to control these interrupts and to get information about
their status.
Video Output
Chapter 7
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