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Flight Software & Embedded Systems Framework

Communication Adapter Interface

Any communication component (e.g. a radio component) that is intended for use with the standard F´ uplink and downlink stack should implement the Communication Adapter Interface. This interface specifies both the ports and protocols used to operate with the standard F´ uplink and downlink components.

Implementors of this interface are referred to as Communication Adapters.

Communication Adapter Interface

The communication adapter interface protocol is designed to work alongside the framer status protocol and the com queue protocol to ensure that data messages do not overload a communication interface. These protocols are discussed below.


The communication adapter interface is composed of three ports. These ports are used to transmit outgoing data through some communication hardware and receive incoming data from that same hardware. These ports share types with the byte stream driver model for backwards compatibility.

Kind Suggested Name Port Type Usage
input comDataIn Drv.ByteStreamSend Port receiving Fw::Buffer objects for outgoing transmission.
output comDataOut Drv.ByteStreamRecv Port producing incoming Fw::Buffer objects.
output comStatus Fw.SuccessCondition Port indicating status of outgoing transmission. See protocol.

Note: components implementing the Communication Adapter Interface must deallocate any Fw::Buffer received on the comDataIn port or must delegate the deallocation to another component (e.g. a driver). See Memory Management in F´

comDataIn Description

This port receives data from an F´ application in the form of an argument of Fw::Buffer type. This data is intended to be sent out the communications interface managed by this component. From the perspective of the application this is the outgoing data port.

comDataOut Description

This port receives data from the communication interface managed by this component and provides it to the F´ application in the form of an argument of Fw::Buffer type. From the perspective of the application this is the incoming data port.

comStatus Description

This port carries a status of Fw::Success::SUCCESS or Fw::Success::FAILURE typically in response to a call to the comDataIn port described above.

Note: it is critical to obey the protocol as described in the protocol section below.

Communication Queue Protocol

Svc::ComQueue queues messages until the communication adapter is ready to receive these messages. For each Fw::Success::SUCCESS message received, Svc::ComQueue will emit one message. Svc::ComQueue will not emit messages at any other time. This implies several things:

  1. An initial Fw::Success::SUCCESS message must be sent to Svc::ComQueue to initiate data flow
  2. A Fw::Success::SUCCESS must be eventually received in response to each message for data to continue to flow

These implications are discussed in more depth in the appropriate protocol sections.

Framer Status Protocol

Framing typically happens between Svc::ComQueue and a communications adapter. The Svc::Framer component implements this protocol in order to interoperate with these other components. The action taken by this protocol is dependent on the number of framed messages (frames) sent to the communication adapter in response to each message received from Svc::ComQueue.

Produced Frames Action Rationale
0 Send one Fw::Success::SUCCESS status Data must continue to flow to produce a frame
1 Pass through received statuses Frame produced and communication adapter produces status

When a frame is produced the communication adapter is responsible for determining the status of the message and its statuses must be passed through. When no frame is produced, the communication adapter does not receive a frame and is incapable of producing a status. Svc::Framer must act appropriately in this case.

Note: Svc::Framer must also pass through the initiation message from the communication adapter to start data flow.

Communication Adapter Protocol

The communication adapter must obey a specific protocol to indicate to F´ application components the status of outgoing transmissions. This is done with the comStatus port. A communication status is one of two possibilities:

Status Description
Fw::Success::SUCCESS Communication adapter transmission succeeded and is ready for more data.
Fw::Success::FAILURE Last transmission failed; communication adapter is unable to receive more data.
  • Fw::Success::SUCCESS may also indicate a connection/reconnection success when data flow must be initiated.

A Communication Adapter shall emit either Fw::Success::SUCCESS or Fw::Success::FAILURE via the comStatus port once for each call received on comDataIn. Additionally, a Communication Adapter shall emit Fw::Success::SUCCESS once at startup to indicate communication is initially ready and once after each Fw::Success::FAILURE event to indicate that communication has been restored. By emitting Fw::Success::SUCCESS after any failure, the communication adapter ensures that each received message eventually results in a Fw::Success::SUCCESS.

It is imperative that Communication Adapters implement the comStatus protocol correctly.