ST STM32L4+ Series Reference Manual page 957

RM0432
30.10 Functional description: virtual channels
The DSI Host supports choosing the Virtual Channel (VC) for use for each interface. Using
multiple Virtual Channels, the system can address multiples displays at the same time,
when each display has a different Virtual Channel identifier.
When the LTDC interface is configured for a particular Virtual Channel, it is possible to use
the APB slave generic interface to issue the commands while the video stream is being
transmitted. With this, it is possible to send the commands through the ongoing video
stream, addressing different virtual channels and thus enable the interface with multiple
displays. During the Video mode, the video stream transmission has the maximum priority.
Therefore, the transmission of sideband packets such as the ones from the Generic
interface are only transported when there is time available within the video stream
transmission. The DSI Host identifies the available time periods and uses them to transport
the Generic interface packets.
from the APB Generic interface within the video stream transmitted by the LTDC interface.
It is also possible to address the multiple displays with only the Generic interface using
different Virtual Channels. Because the Generic interface is not restricted to any particular
Virtual Channel through configuration, it is possible to issue the packets with different Virtual
Channels. This enables the interface to time multiplex the packets to be provided to the
displays with different Virtual Channels.
You can use the following configuration registers to select the Virtual Channel ID associated
with transmissions over the LTDC and APB slave generic interfaces:
•
DSI_LVCID.VCID field configures the Virtual Channel ID that is indexed to the Video
mode packets using the LTDC interface.
•
DSI_GHCR register configures the Packet Header (which includes the Virtual Channel
ID to be used) for transmissions using APB slave generic interface.
• DSI_GVIDR.VCID field configures the Virtual Channel ID of the read responses to
store and return to the Generic interface.
DSI Host (DSIHOST) applied to STM32L4R9xx and STM32L4S9xx only
Figure 230
Figure 230. Command transmission by the generic interface
RM0432 Rev 6
illustrates where the DSI Host inserts the packets
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