betaflight/docs/API/DisplayPort.md

DisplayPort MSP Extensions

Betaflight supports what is sometimes referred to as Canvas Mode whereby the OSD can send arbitrary character strings to be displayed at given screen coordinates.

DisplayPort MSP commands

MSP_SET_OSD_CANVAS

The MSP_SET_OSD_CANVAS command is sent by the VTX, or display device, to the FC to indicate the size of the canvas available to the DisplayPort rendering when in HD mode. HD mode, as is indicated by vcd_video_system = HD is automatically set on reception of this command.

Command	Msg Id	Direction	Notes
MSP_SET_OSD_CANVAS	188	to FC	Sets the canvas size

Data	Type	Notes
canvas_cols	uint8	The number of columns
canvas_rows	uint8	The number of rows

sequenceDiagram
    participant FC
    participant VTX
    FC->>VTX: MSP_DP_HEARTBEAT sent and detected
    VTX->>FC: MSP_SET_OSD_CANVAS set rows/columns
    FC->>VTX: MSP request success

MSP_OSD_CANVAS

The MSP_OSD_CANVAS command is sent by the configurator to the FC to determine the size of the canvas available to the DisplayPort rendering when in HD mode. This is then used on the OSD tab to show the correct number of rows/columns when editing the OSD element positions.

Command	Msg Id	Direction	Notes
MSP_OSD_CANVAS	189	to FC	Gets the canvas size

Response is two bytes.

Data	Type	Notes
canvas_cols	uint8	The number of columns
canvas_rows	uint8	The number of rows

sequenceDiagram
    participant FC
    participant Configurator
    participant Preview
    Configurator->>FC: Configurator connects to FC
    Configurator->>FC: MSP_OSD_CANVAS get rows/columns
    Configurator->>Preview: OSD Preview pane resized 

MSP_DISPLAYPORT

The MSP_DISPLAYPORT command is sent by the FC to the display device/VTX to perform a DisplayPort operation.

Command	Msg Id	Direction	Notes
MSP_DISPLAYPORT	182	from FC	DisplayPort specific commands follow

One of the following sub-commands will then follow.

DisplayPort sub-commands

MSP_DP_HEARTBEAT

Command	Msg Id	Notes
MSP_DP_HEARTBEAT	0	Prevent OSD Slave boards from displaying a 'disconnected' status

MSP_DP_RELEASE

Command	Msg Id	Notes
MSP_DP_RELEASE	1	Clears the display and allows local rendering on the display device based on telemetry informtation etc.

MSP_DP_CLEAR_SCREEN

Command	Msg Id	Notes
MSP_DP_CLEAR_SCREEN	2	Clear the display

MSP_DP_WRITE_STRING

Command	Msg Id	Notes
MSP_DP_WRITE_STRING	3	Write a string

Data	Type	Notes
row	uint8	Row on which to position the first character of the string
column	uint8	Column on which to position the first character of the string
attribute	uint8	Byte indicating the font to use and if the text should flash
string	uint8 x n	NULL terminated string of up to 30 characters in length

The attribute parameter is encoded thus.

Field	Bits	Comment
Version	7	Must be 0
DISPLAYPORT_MSP_ATTR_BLINK	6	Set to have the display device automatically blink the string
Reserved	2 - 5	Must be 0
Font number	0 - 1	Selects one of four fonts, each of 256 8 bit characters

MSP_DP_DRAW_SCREEN

Command	Msg Id	Notes
MSP_DP_DRAW_SCREEN	4	Triggers the display of a frame after it has been cleared/rendered

MSP_DP_OPTIONS

Command	Msg Id	Notes
MSP_DP_OPTIONS	5	Not used by Betaflight. Used by INAV and Ardupilot to set display resolution.

MSP_DP_SYS

Command	Msg Id	Notes
MSP_DP_SYS	6	Display system element displayportSystemElement_e at given coordinates

Data	Type	Notes
row	uint8	Row on which to position the first character of the string
column	uint8	Column on which to position the first character of the string
system_element	uint8	System element to be rendered by the VTX/goggle/display device

system_element will be one of the following as defined by displayPortSystemElement_e . Once one MSP_DP_SYS sub-command has been received by the VTX/goggle/display device then the default system elements should no longer be displayed in their default locations, but only explicitly as directed by this command. In this way, the default behaviour is as before, but as soon as any system element is explicitly positioned these OSD elements behave just like any other and can be called up is specific locations by any given OSD profile.

// System elements rendered by VTX or Goggles
typedef enum {
    DISPLAYPORT_SYS_GOGGLE_VOLTAGE = 0,
    DISPLAYPORT_SYS_VTX_VOLTAGE = 1,
    DISPLAYPORT_SYS_BITRATE = 2,
    DISPLAYPORT_SYS_DELAY = 3,
    DISPLAYPORT_SYS_DISTANCE = 4,
    DISPLAYPORT_SYS_LQ = 5,
    DISPLAYPORT_SYS_GOGGLE_DVR = 6,
    DISPLAYPORT_SYS_VTX_DVR = 7,
    DISPLAYPORT_SYS_WARNINGS = 8,
    DISPLAYPORT_SYS_VTX_TEMP = 9,
    DISPLAYPORT_SYS_FAN_SPEED = 10,
    DISPLAYPORT_SYS_COUNT,
} displayPortSystemElement_e;