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:

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:

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 compCmdStat port. The sequence number is matched to the entry in the pending command table, and the seqCmdStatus output port corresponding to the source port is called (if it is connected) with the status and the context value. Note #1: this requires that the component sending the command buffer have connections to the same seqCmdBuff and seqCmdStatus port numbers. Note #2: the seqCmdStatus port utilize the same type as the compCmdStat, the Fw::CmdResponse. This has been done to avoid creation of similar types for status ports. However, the Fw::CmdResponse::cmdSeq argument of the seqCmdStatus doesn't have any meaning for the calling sequencer. Therefore, as it has been mentioned before, instead of forwarding a command sequence number, the context value is transferred.

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: seqCmdBuff()
    activate Command Buffer Source
    activate CommandDispatcher
    CommandDispatcher->>Component: seqCmdBuff()
    activate Component
    Component->>CommandDispatcher: compCmdStat()
    deactivate Component
    CommandDispatcher->>Command Buffer Source: seqCmdStatus()
    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

5. Unit Testing

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

6. Change Log