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Add documentation for Multi GCS protocol (Draft) #556

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Multi GCS: include multi_gcs.md in en/SUMMARY.md and en/README.md
Davidsastresas Oct 17, 2024
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Multi GCS: add multi_gcs.md
Davidsastresas Oct 17, 2024
5ff6884
SUMMARY.md: mark Multi GCS as WIP
Davidsastresas Oct 23, 2024
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README.md: mark Multi GCS as WIP
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multi_gcs.md: link to descriptions in Introduction
Davidsastresas Oct 23, 2024
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1 change: 1 addition & 0 deletions en/SUMMARY.md
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Expand Up @@ -81,5 +81,6 @@
* [Traffic Management (UTM/ADS-B)](services/traffic_management.md)
* [Events Interface (WIP)](services/events.md)
* [Time Synchronization](services/timesync.md)
* [Multi GCS Control Protocol](services/multi_gcs.md)
* [Contributing](contributing/contributing.md)
* [Support](about/support.md)
1 change: 1 addition & 0 deletions en/services/README.md
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Expand Up @@ -42,3 +42,4 @@ The main microservices are shown in the sidebar (most are listed below):
- [Events Interface (WIP)](../services/events.md)
- [Time Synchronization](../services/timesync.md)
- [Illuminator Protocol](../services/illuminator.md)
- [Multi GCS Control Protocol](../services/multi_gcs.md)
128 changes: 128 additions & 0 deletions en/services/multi_gcs.md
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@@ -0,0 +1,128 @@
# Multi GCS protocol
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Can you make your repo accept change requests from master? That would allow me to subedit freely (ideally) and merge comments. Likely to be much faster and less work on you.

## Introduction
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@hamishwillee hamishwillee Oct 22, 2024 •
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Might be worth first starting with the "use case" like:

This protocol allows a GCS to request control of a MAVLink system from a single component (usually the autopilot), and for the other components of the system to determine the controlling GCS and set their controlling GCS to match.
Note that the API only provides mechanisms for managing and handing over control of the system: it does not provide any security layer.

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FYI, need to change the "autopilot" focus if we allow the CONTROL_STATUS to be emitted by other components.

A controlled vehicle should only accept MAVLink commands (or command-like messages) that are sent by the controlling GCS, or from other components with the same system id. Commands from other system should be rejected with MAV_RESULT_PERMISSION_DENIED (except for this command, which may be acknowledged with MAV_RESULT_ACCEPTED if control is granted).

The command is sent by a GCS to the autopilot component to request or release control of a system, specifying whether subsequent takeover requests from another GCS are automatically granted, or require permission.
The autopilot should grant control to the GCS if the system does not require takeover permission (or is uncontrolled) and ACK the request with MAV_RESULT_ACCEPTED.

The autopilot should stream CONTROL_STATUS indicating its controlling system: all other components with the same system id should monitor this message and set their own owner to match that of the autopilot.
If the autopilot cannot grant control (because takeover requires permission), the request should be rejected with MAV_RESULT_PERMISSION_DENIED.

The autopilot should then send this same command to the current owning GCS in order to notify of the request.
The owning GCS would ACK with MAV_RESULT_ACCEPTED, and might choose to release ownership of the vehicle, or re-request ownership with the takeover bit set to allow permission.

Note that the pilots of both GCS should co-ordinate safe handover offline.
It is also possible for a GCS to request control of a specific component rather than the whole system (though this is not recommended).
In this case the command should be sent to the specific component, which should also emit CONTROL_STATUS to indicate its owner (this component would ignore the CONTROL_STATUS set by the autopilot).
The flow is otherwise the same.
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We also need to add that:

  • System can be uncontrolled
  • If the autopilot ('controlling component') loses its connection to the controlling GCS we need to make it clear how the ownership lapses.
    • IMO we don't want a GCS that has been turned off to be the controller, but nor do we want a vehicle that flies out of range and then starts to return to have no owner (though this is not critical as a vehicle will accept commands from any GCS if it has not owner)
    • So I "think" maybe a model like: after short connection break, set takeover allowed. After a bit longer, make uncontrolled.


### Multi GCS protocol messages
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@hamishwillee hamishwillee Oct 22, 2024 •
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We have standard names for some of these. Note all headings are first letter of each word capitalised and should "by default" indent by one level from previous (ie this is H2).

Suggested change
### Multi GCS protocol messages
## Message/Enum Summary


This is the set of messages and commands used on this protocol.

| Message | Description |
| ------------------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| <a id="CONTROL_STATUS"></a>[CONTROL_STATUS](../messages/development.md#CONTROL_STATUS) | Information about GCS in control of this MAV. This should be broadcast at low rate (nominally 1 Hz) and emitted when ownership or takeover status change. Control over MAV is requested using MAV_CMD_REQUEST_OPERATOR_CONTROL. |

| Command | Description |
| ------------------------------------------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| <a id="MAV_CMD_REQUEST_OPERATOR_CONTROL"></a>[MAV_CMD_REQUEST_OPERATOR_CONTROL](../messages/development.md#MAV_CMD_REQUEST_OPERATOR_CONTROL) | Request control of a system.

### Workflow diagrams
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Let's add some more structure. Maybe also add workflow where no GCS is in control, and for control of a specific component? Maybe also a heading for "Vehicle loses connection" (with no diagram)

Suggested change
### Workflow diagrams
## Operations
### Request Control When Takeover Allowed

Diagram 1 - 2 GCS, one of them asks for control without enforcing being asked before other GCS takes over (MAV_CMD_REQUEST_OPERATOR_CONTROL param 3 = 1)

<!-- Mermaid graph:
sequenceDiagram;
participant GCS - 253
participant Vehicle - 1
participant GCS - 250
note over Vehicle - 1: Broadcast CONTROL_STATUS: Nobody in control <br> - Sysid In control: 0
Vehicle - 1->>GCS - 253: CONTROL_STATUS <br> - sysid_in_control: 0
Vehicle - 1->>GCS - 250: CONTROL_STATUS <br> - sysid_in_control: 0
Note over GCS - 253: GCS 253 wants to request control <br> not enforcing asking for takeover
GCS - 253->>Vehicle - 1: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 0 (Sysid requesting control not needed, can be deducted from sender) <br> - param 2: 1 (request control) <br> - param 3: 1 (allow automatic takeover)
Vehicle - 1->>GCS - 253: COMMAND_ACK
Note over Vehicle - 1: Control is transfered to GCS 253
Vehicle - 1->>GCS - 250: CONTROL_STATUS <br> - sysid_in_control: 253 <br> - takeover_allowed: 1 (takeover allowed automatically)
Vehicle - 1->>GCS - 253: CONTROL_STATUS <br> - sysid_in_control: 253 <br> - takeover_allowed: 1 (takeover allowed automatically)
Note over GCS - 253: It is now in control of vehicle 1
Note over GCS - 250: Now GCS 250 wants to request control. <br> As GCS 253 didn't enforce being asked, <br> it will be granted automatically.
GCS - 250->>Vehicle - 1: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 0 (Sysid requesting control not needed, can be deducted from sender) <br> - param 2: 1 (request control) <br> - param 3: 1 (allow automatic takeover, although irrelevant right now)
Vehicle - 1->>GCS - 250: COMMAND_ACK
Note over Vehicle - 1: As asking for takeover wasn't enforced by GCS 253, <br> control is granted automatically.
Vehicle - 1->>GCS - 253: CONTROL_STATUS <br> - sysid_in_control: 250 <br> - takeover_allowed: 1 (takeover allowed automatically)
Vehicle - 1->>GCS - 250: CONTROL_STATUS <br> - sysid_in_control: 250 <br> - takeover_allowed: 1 (takeover allowed automatically)
-->

[![](https://mermaid.ink/img/pako:eNrdVV9v2jAQ_yqnvKxItAqt9pJNSBmgqdqAjdA-IUUmvoDVxGaOA0JVv_vO4KSQlbWT2B7GC87Zd_n9uXMevURx9AKvwB8lygT7gi00yz_MJNBvxbQRiVgxaeBzL4JLuH5_8-vWPS5FkiFtd07n-fstqQyCWqM-zArgk1aMJ6ww0BuPppPx1ziahtO7KICRmiu-BSEhUdJolcHHue5SVrQtBIfbOh6Ae8VB4ctut8YdNEpXdQpbJxYyflsd_w_qwL7QqOZ8AMYuaQEbEqkAo0BbC0iAI5okF6BMlU6EXAArHuwfPYJhD2hL7t9Q1yWgR7oOw_u4N-zHk8H3u0E0jcffBpNwOp7EjkNQoSfLWG4zfLjYK-vw2BdWkCwaiciRtyFhEuYItC4TgxxSrXIoUHLUreOi1wF04KJBr3HmZneGZZnaACuNyhk1UE2y9aqxw2E46sdh70tT8SM1eo6HIME1k0WKmpCT9s6MM_lubXWbFYN4Rw35jmYVBBd8ZkyBbetMXXwWFC-27q2xCkqy6mAqVQprB7lzKte347xxavsnW_9qjzss6iHhgst31SQg9Z2bBtuIu7PCwEZkme1Iur-kadK5Op4T__-ckzZ5aZaqXCxBaI0Zru0NrMViaaxdrVf7-21jRMa8cBORncWBSRzm28o_Z1LyPH6_M-kMne__rfnz_xkKr-3lqHMmOH2eHy2mmWeWmOPMC2jJMWVlZmbeTD7RUZsbbWXiBUaX2Pa0bQIvSFlW0FO54sxU3_ZGdMCFUdoFn34CXbSSUw?type=png)](https://mermaid-js.github.io/mermaid-live-editor/edit#pako:eNrdVV9v2jAQ_yqnvKxItAqt9pJNSBmgqdqAjdA-IUUmvoDVxGaOA0JVv_vO4KSQlbWT2B7GC87Zd_n9uXMevURx9AKvwB8lygT7gi00yz_MJNBvxbQRiVgxaeBzL4JLuH5_8-vWPS5FkiFtd07n-fstqQyCWqM-zArgk1aMJ6ww0BuPppPx1ziahtO7KICRmiu-BSEhUdJolcHHue5SVrQtBIfbOh6Ae8VB4ctut8YdNEpXdQpbJxYyflsd_w_qwL7QqOZ8AMYuaQEbEqkAo0BbC0iAI5okF6BMlU6EXAArHuwfPYJhD2hL7t9Q1yWgR7oOw_u4N-zHk8H3u0E0jcffBpNwOp7EjkNQoSfLWG4zfLjYK-vw2BdWkCwaiciRtyFhEuYItC4TgxxSrXIoUHLUreOi1wF04KJBr3HmZneGZZnaACuNyhk1UE2y9aqxw2E46sdh70tT8SM1eo6HIME1k0WKmpCT9s6MM_lubXWbFYN4Rw35jmYVBBd8ZkyBbetMXXwWFC-27q2xCkqy6mAqVQprB7lzKte347xxavsnW_9qjzss6iHhgst31SQg9Z2bBtuIu7PCwEZkme1Iur-kadK5Op4T__-ckzZ5aZaqXCxBaI0Zru0NrMViaaxdrVf7-21jRMa8cBORncWBSRzm28o_Z1LyPH6_M-kMne__rfnz_xkKr-3lqHMmOH2eHy2mmWeWmOPMC2jJMWVlZmbeTD7RUZsbbWXiBUaX2Pa0bQIvSFlW0FO54sxU3_ZGdMCFUdoFn34CXbSSUw)

Diagram 2 - Now one of them asks for control enforcing being asked before other GCS takes over. When the other GCS takes over, the original GCS in control just requests again control without enforcing being asked before. This situation is interesting so the vehicle is never with no GCS in control. An alternative approach is in diagram 3.
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Suggested change
Diagram 2 - Now one of them asks for control enforcing being asked before other GCS takes over. When the other GCS takes over, the original GCS in control just requests again control without enforcing being asked before. This situation is interesting so the vehicle is never with no GCS in control. An alternative approach is in diagram 3.
### Request Control When Takeover Not Allowed
Diagram 2 - Now one of them asks for control enforcing being asked before other GCS takes over. When the other GCS takes over, the original GCS in control just requests again control without enforcing being asked before. This situation is interesting so the vehicle is never with no GCS in control. An alternative approach is in diagram 3.


<!-- mermaid graph:
sequenceDiagram;
participant GCS - 253
participant Vehicle - 1
participant GCS - 250
Vehicle - 1->>GCS - 253: CONTROL_STATUS <br> - sysid_in_control: 0
Vehicle - 1->>GCS - 250: CONTROL_STATUS <br> - sysid_in_control: 0
Note over GCS - 253: GCS 253 wants to request control <br> ENFORCING asking for takeover first
GCS - 253->>Vehicle - 1: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 0 (Sysid requesting control not needed, can be deducted from sender) <br> - param 2: 1 (request control) <br> - param 3: 0 (Do not allow automatic takeover, ask first)
Vehicle - 1->>GCS - 253: COMMAND_ACK
Note over Vehicle - 1: Control is transfered to GCS 253
Vehicle - 1->>GCS - 250: CONTROL_STATUS <br> - sysid_in_control: 253 <br> - takeover_allowed: 0 (automatic takeover not allowed, ask first)
Vehicle - 1->>GCS - 253: CONTROL_STATUS <br> - sysid_in_control: 253 <br> - takeover_allowed: 0 (automatic takeover not allowed, ask first)
Note over GCS - 253: It is now in control of vehicle 1
Note over GCS - 250: Now GCS 250 wants to request control
GCS - 250->>Vehicle - 1: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 0 (Sysid requesting control not needed, can be deducted from sender) <br> - param 2: 1 (request control) <br> - param 3: 1 (allow automatic takeover, although irrelevant at this point)
Vehicle - 1->>GCS - 250: COMMAND_ACK
Vehicle - 1->>GCS - 253: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 250 (Sysid requesting control) <br> - param 2: 1 (request control) <br> - param 3: 1 (allow automatic takeover, although irrelevant at this point)
Note over GCS - 253: Popup appears in GCS comunicating the request from GCS 250. <br>User accepts. Requesting control again without enforcint being asked for takeover
GCS - 253->>Vehicle - 1: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 0 (Sysid requesting control not needed, can be deducted from sender) <br> - param 2: 1 (request control) <br> - param 3: 1 (allow automatic takeover)
Vehicle - 1->>GCS - 253: COMMAND_ACK
Vehicle - 1->>GCS - 250: CONTROL_STATUS <br> - sysid_in_control: 253 <br> - takeover_allowed: 1 (automatic takeover allowed)
Vehicle - 1->>GCS - 253: CONTROL_STATUS <br> - sysid_in_control: 253 <br> - takeover_allowed: 1 (automatic takeover allowed)
Note over GCS - 250: As vehicle is reporting now automatic takeover <br> is allowed, we are free to request control
GCS - 250->>Vehicle - 1: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 0 (Sysid requesting control not needed, can be deducted from sender) <br> - param 2: 1 (request control) <br> - param 3: 0 (do not allow automatic takeover, although irrelevant at this point)
Vehicle - 1->>GCS - 250: COMMAND_ACK
Note over Vehicle - 1: Control will be granted automatically now
Vehicle - 1->>GCS - 253: CONTROL_STATUS <br> - sysid_in_control: 250 <br> - takeover_allowed: 1 (allow automatic takeover)
Vehicle - 1->>GCS - 250: CONTROL_STATUS <br> - sysid_in_control: 250 <br> - takeover_allowed: 1 (allow automatic takeover)
-->

[![](https://mermaid.ink/img/pako:eNrdV9FO2zAU_ZWrPIFUUAraSzYhVW2H0NaWtYWnSpFxblqLxM5shwoh_n3XSZqVkpZ1YqDRJze2r8-55-TIefC4itALPIM_c5Qce4LNNUs_zyTQL2PaCi4yJi2cdydwBCefTp9PXeNC8ARpur19n19Ora09OjuriwbQHQ2n49H3cDLtTK8m8OVGn9GUuTciCoUMuZJWqySAnXX8PepAWWioLIK6Qw1rYNyQBrAkBgasAu36YyxU28uy_eHX0bh7MTwHZm6FnEOsNFh2i0W5WGhjyzPqygR1DXgAg8512B30wnH_x1V_Mg1Hl_1xZzoahxWLYIWfOspSt8OHg4njskLkjl2BksqCRIwwagFnEm4QaJxzixHEWqVgUEaoD58WPQmgDQcbBDfWnBYH91RxBEsStQSWW5Uykrlm3HJtKGkfvij2YNAZ9sJO99umCk_6062YCRJBM2li1MSF9KgEeiUvOKmryRWZsGCJUUH8OdffjXDN3oP3-wBqNPmFdX2VpKWQtYdUDHcV-va2vdTZIe0qNfC3viRPve__x96nNTtMn9iFyucLEFpjgncu9JgFu6DmZkrI3abwG16GrfbZv2VOn61Ne8dmNBryUmV5BizLkGnjTOnmuEpzKTgrgNsF1i4rVK08eFygvDJUj3GOmTXHMH5uEjZnVHUpHEYLKCmvOWEis7hV9NI4s6xl-MdJ7x2i7Z3V_zZu243pVk2_Sb7-CYLGUOyYOjvJ7hozpQuFZWPfSwC0sE7tJQLTSGIjNt054OMEKh0cvXiZePVcfeGSsRRJ4mjSBVg6ljUownjvRHw18_m7zfc3L6r_Bud7LS9FnTIR0RfDg0Mz8yiRU5x5AQ0jjFme2Jk3k4-01BWY3EvuBVbn2PK0E9MLYpYY-pdnEbOrz42Np_1IWKWrh4-_AIxLByI?type=png)](https://mermaid-js.github.io/mermaid-live-editor/edit#pako:eNrdV9FO2zAU_ZWrPIFUUAraSzYhVW2H0NaWtYWnSpFxblqLxM5shwoh_n3XSZqVkpZ1YqDRJze2r8-55-TIefC4itALPIM_c5Qce4LNNUs_zyTQL2PaCi4yJi2cdydwBCefTp9PXeNC8ARpur19n19Ora09OjuriwbQHQ2n49H3cDLtTK8m8OVGn9GUuTciCoUMuZJWqySAnXX8PepAWWioLIK6Qw1rYNyQBrAkBgasAu36YyxU28uy_eHX0bh7MTwHZm6FnEOsNFh2i0W5WGhjyzPqygR1DXgAg8512B30wnH_x1V_Mg1Hl_1xZzoahxWLYIWfOspSt8OHg4njskLkjl2BksqCRIwwagFnEm4QaJxzixHEWqVgUEaoD58WPQmgDQcbBDfWnBYH91RxBEsStQSWW5Uykrlm3HJtKGkfvij2YNAZ9sJO99umCk_6062YCRJBM2li1MSF9KgEeiUvOKmryRWZsGCJUUH8OdffjXDN3oP3-wBqNPmFdX2VpKWQtYdUDHcV-va2vdTZIe0qNfC3viRPve__x96nNTtMn9iFyucLEFpjgncu9JgFu6DmZkrI3abwG16GrfbZv2VOn61Ne8dmNBryUmV5BizLkGnjTOnmuEpzKTgrgNsF1i4rVK08eFygvDJUj3GOmTXHMH5uEjZnVHUpHEYLKCmvOWEis7hV9NI4s6xl-MdJ7x2i7Z3V_zZu243pVk2_Sb7-CYLGUOyYOjvJ7hozpQuFZWPfSwC0sE7tJQLTSGIjNt054OMEKh0cvXiZePVcfeGSsRRJ4mjSBVg6ljUownjvRHw18_m7zfc3L6r_Bud7LS9FnTIR0RfDg0Mz8yiRU5x5AQ0jjFme2Jk3k4-01BWY3EvuBVbn2PK0E9MLYpYY-pdnEbOrz42Np_1IWKWrh4-_AIxLByI)

Diagram 3 - Now one of them asks for control enforcing being asked before other GCS takes over. When the other GCS takes over, the original GCS in control just releases control. This might be desirable in some situations, but leaves the vehicle with no owner until the second GCS requests control:

<!-- mermaid graph:
sequenceDiagram;
participant GCS - 253
participant Vehicle - 1
participant GCS - 250
Vehicle - 1->>GCS - 253: CONTROL_STATUS <br> - sysid_in_control: 0
Vehicle - 1->>GCS - 250: CONTROL_STATUS <br> - sysid_in_control: 0
Note over GCS - 253: GCS 253 wants to request control <br> ENFORCING asking for takeover first
GCS - 253->>Vehicle - 1: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 0 (Sysid requesting control not needed, can be deducted from sender) <br> - param 2: 1 (request control) <br> - param 3: 0 (Do not allow automatic takeover, ask first)
Vehicle - 1->>GCS - 253: COMMAND_ACK
Note over Vehicle - 1: Control is transfered to GCS 253
Vehicle - 1->>GCS - 250: CONTROL_STATUS <br> - sysid_in_control: 253 <br> - takeover_allowed: 0 (automatic takeover not allowed, ask first)
Vehicle - 1->>GCS - 253: CONTROL_STATUS <br> - sysid_in_control: 253 <br> - takeover_allowed: 0 (automatic takeover not allowed, ask first)
Note over GCS - 253: It is now in control of vehicle 1
Note over GCS - 250: Now GCS 250 wants to request control
GCS - 250->>Vehicle - 1: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 0 (Sysid requesting control not needed, can be deducted from sender) <br> - param 2: 1 (request control) <br> - param 3: 1 (allow automatic takeover, although irrelevant at this point)
Vehicle - 1->>GCS - 250: COMMAND_ACK
Vehicle - 1->>GCS - 253: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 250 (Sysid requesting control) <br> - param 2: 1 (request control) <br> - param 3: 1 (allow automatic takeover, although irrelevant at this point)
Note over GCS - 253: Popup appears in GCS comunicating the request from GCS 250. <br>User accepts. Releasing control
GCS - 253->>Vehicle - 1: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 0 (Sysid requesting control not needed, can be deducted from sender) <br> - param 2: 0 (release control) <br> - param 3: 1 (allow automatic takeover, although it doesn't apply as we drop control)
Vehicle - 1->>GCS - 253: COMMAND_ACK
Note over Vehicle - 1: Nobody in control now
Vehicle - 1->>GCS - 250: CONTROL_STATUS <br> - sysid_in_control: 0 <br> - takeover_allowed: 1 (automatic takeover allowed)
Vehicle - 1->>GCS - 253: CONTROL_STATUS <br> - sysid_in_control: 0 <br> - takeover_allowed: 1 (automatic takeover allowed)
Note over GCS - 250: As vehicle is reporting now nobody in control <br> We are free to request control
GCS - 250->>Vehicle - 1: MAV_CMD_REQUEST_OPERATOR_CONTROL: <br> - param 1: 0 (Sysid requesting control not needed, can be deducted from sender) <br> - param 2: 1 (request control) <br> - param 3: 0 (do not allow automatic takeover, although irrelevant at this point)
Vehicle - 1->>GCS - 250: COMMAND_ACK
Note over Vehicle - 1: Control will be granted automatically now, as <br> nobody is in control
Vehicle - 1->>GCS - 253: CONTROL_STATUS <br> - sysid_in_control: 250 <br> - takeover_allowed: 1 (allow automatic takeover)
Vehicle - 1->>GCS - 250: CONTROL_STATUS <br> - sysid_in_control: 250 <br> - takeover_allowed: 1 (allow automatic takeover)
-->

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