Svc::CmdDispatcher Component

1. Introduction

The Svc::CmdDispatcher is responsible for dispatching incoming commands to the components that implement those commands. The commands are sent in encoded Fw::Com form from an external sender like a ground system or a sequencer. The dispatcher decodes the packet and extracts the opcode. This opcode is looked up in a table and dispatched to the component via a port indicated in the table. The output port for each opcode is set by a call to a registration port.

2. Requirements

The requirements for Svc::CmdDispatcher are as follows:

Requirement	Description	Verification Method
CD-001	The Svc::CmdDispatcher component shall accept command buffers and decode them into commands	Inspection, Unit Test
CD-002	The Svc::CmdDispatcher component shall dispatch commands to components	Unit Test
CD-003	The Svc::CmdDispatcher component shall provide an interface to register commands	Inspection
CD-004	The Svc::CmdDispatcher component shall process command status from components and report the results to the command buffer sender.	Unit Test

3. Design

3.1 Context

3.1.1 Component Diagram

The Svc::CmdDispatcher component has the following component diagram:

3.1.2 Ports

The Svc::CmdDispatcher component uses the following port types:

Port Data Type	Name	Direction	Kind	Usage
Fw::Cmd	cmdSend	Output	n/a	Send commands to components
Fw::CmdResponse	compStat	Input	Asynchronous	Port for components to report command status
Fw::CmdResponse	seqStatus	Output	n/a	Send command status to command buffer source
Fw::Com	cmdBuff	Input	Asynchronous	Receive command buffer
Fw::CmdReg	cmdReg	Input	Synchronous	Command Registration

3.2 Functional Description

The Svc::CmdDispatcher component provides command dispatching. The architecture autocoder generates port instances for components that specify commands that implement the commanding pattern. Svc::CommandDispatcher implements the command decoding and dispatching to supply the components with commands.

3.2.1 Command Registration

An autogenerated function on components create a public function regCommands that tells components to register the set of op codes that are implemented by the component. The autogenerated port is connected to the compCmdReg input port on Svc::CmdDispatcher that corresponds to the number of the compCmdSend port used to dispatch commands. The port handler looks through the dispatch table for an unused entry and adds the opcode. It maps the opcode to the dispatch port number corresponding to the registration port number.

3.2.2 Command Dispatch

When the command dispatcher receives a command buffer, it decodes the opcode. It searches the dispatch table for the opcode, then assigns a sequence number to the command and stores the opcode, sequence number, context value and source port in a pending command table. The command is then dispatched to the component that implements the command. When the component completes execution of the command, it reports the status back via the compStat port. The sequence number is matched to the entry in the pending command table, and the seqStatus output port corresponding to the source port is called (if it is connected) with the status and the context value. Note that this requires that the component sending the command buffer have connections to the same cmdBuff and seqStatus port numbers.

3.3 Scenarios

3.3.1 Command Registration

The Svc::CmdDispatcher component accepts command registration from other components:

sequenceDiagram
    Initialization->>Component: get_ComdReg_InputPort()
    activate Initialization
    deactivate Initialization
    activate Component
    deactivate Component
    Initialization->>Component: regCommands()
    activate Initialization
    activate Component
    loop for each opcode
        Component->>CommandDispatcher: cmdReg()
    end
    deactivate Initialization
    deactivate Component

3.3.1 Dispatch Commands

The Svc::CmdDispatcher component dispatches commands to other components:

sequenceDiagram
    Command Buffer Source->>CommandDispatcher: cmdBuff()
    activate Command Buffer Source
    activate CommandDispatcher
    CommandDispatcher->>Component: cmdBuff()
    activate Component
    Component->>CommandDispatcher: comStat()
    deactivate Component
    CommandDispatcher->>Command Buffer Source: seqStatus()
    deactivate CommandDispatcher
    deactivate Command Buffer Source

3.4 State

Svc::CmdDispatcher has no state machines.

3.5 Algorithms

Svc::CmdDispatcher has no significant algorithms.

4. Module Checklists

Checklist
Design
Code
Unit Test

5. Unit Testing

To see unit test coverage run fprime-util check --coverage

6. Change Log

Date	Description
6/25/2015	Design review edits
7/22/2015	Design review actions
9/16/2015	Unit Test additions
1/28/2016	Added context value discussion
5/17/2021	Added CMD Reregistration option