Svc::DpWriter Component

Svc::DpWriter (Active Component)

1. Introduction

Svc::DpWriter is an active component for writing data products to disk. It does the following:

1. Receive buffers containing filled data product containers. The buffers typically come from one or more components that produce data products. They typically pass through an instance of Svc::DpManager, and possibly through an instance of Svc::BufferAccumulator, before reaching DpWriter.

1. For each buffer B received in step 1:
   1. Perform any requested processing, such as data compression, on B.
   1. Write B to disk.

2. Requirements

Requirement	Description	Rationale	Verification Method
SVC-DPWRITER-001	Svc::DpWriter shall provide a port for receiving Fw::Buffer objects pointing to filled data product containers.	The purpose of DpWriter is to write the data products to disk.	Unit Test
SVC-DPWRITER-002	Svc::DpWriter shall provide an array of ports for sending Fw::Buffer objects for processing.	This requirement supports downstream processing of the data in the buffer.	Unit Test
SVC-DPWRITER-003	On receiving a data product container C, Svc::DpWriter shall use the processing type field of the header of C to select zero or more processing ports to invoke, in port order.	The processing type field is a bit mask. A one in bit 2^n in the bit mask selects port index n.	Unit Test
SVC-DPWRITER-004	On receiving an Fw::Buffer B, and after performing any requested processing on B, Svc::DpWriter shall write B to disk.	The purpose of DpWriter is to write data products to the disk.	Unit Test
SVC-DPWRITER-005	Svc::DpManager shall provide telemetry that reports the number of data products written and the number of bytes written.	This requirement establishes the telemetry interface for the component.	Unit test

3. Design

3.1. Component Diagram

The diagram below shows the DpWriter component.

3.2. Ports

DpWriter has the following ports:

Kind	Name	Port Type	Usage
async input	schedIn	Svc.Sched	Schedule in port
async input	bufferSendIn	Fw.BufferSend	Port for receiving data products to write to disk
output	procBufferSendOut	[DpWriterNumProcPorts] Fw.BufferSend	Port for processing data products
output	deallocBufferSendOut	Fw.BufferSend	Port for deallocating data product buffers
time get	timeGetOut	Fw.Time	Time get port
telemetry	tlmOut	Fw.Tlm	Telemetry port
event	eventOut	Fw.Log	Event port
text event	textEventOut	Fw.LogText	Text event port

3.3. State

DpWriter maintains the following state:

1. numDataProducts (U32): The number of data products written.

1. numBytes (U64): The number of bytes written.

3.4. Compile-Time Setup

The configuration constant DpWriterNumProcPorts specifies the number of ports for connecting components that perform processing.

3.5. Runtime Setup

The config function specifies the following constants:

1. fileNamePrefix (string): The prefix to use for file names.

1. fileNameSuffix (string): The suffix to use for file names.

3.6. Port Handlers

3.6.1. schedIn

This handler sends out the state variables as telemetry.

3.6.2. bufferSendIn

This handler receives a mutable reference to a buffer B. It does the following:

1. Check that B is valid and that the first sizeof(FwPacketDescriptorType) bytes of the memory referred to by B hold the serialized value Fw_PACKET_DP. If not, emit a warning event.

1. If step 1 succeeded, then
   1. Read the ProcType field out of the container header stored in the memory pointed to by B. If the value is a valid port number N for procBufferSendOut, then invoke procBufferSendOut at port number N, passing in B. This step updates the memory pointed to by B in place.
   1. Write B to a file, using the format described in the **File Format** section. For the time stamp, use the time provided by timeGetOut.

1. Send B on deallocBufferSendOut.

4. File Format

4.1. Data Format

Each file stores a serialized data product record, with the format described in the data products documentation.

4.2. File Name

The name of each file consists of fileNamePrefix followed by an ID, a time stamp, and fileNameSuffix. The ID consists of an underscore character _ followed by the container ID. The time stamp consists of an underscore character _ followed by a seconds value, an underscore character, and a microseconds value.

For example, suppose that the file name prefix is container_data and the file name suffix is .dat. Suppose that container ID is 100, the seconds value is 100000, and the microseconds value is 1000. Then the file name is container_data_100_100000_1000.dat.

5. Ground Interface

5.1. Telemetry

Name	Type	Description
NumDataProducts	U32	The number of data products handled
NumBytes	U64	The number of bytes handled

5.2. Events

Name	Severity	Description
BufferTooSmall	warning high	Incoming buffer is too small to hold a data product container
InvalidPacketDescriptor	warning high	Incoming buffer had an invalid packet descriptor

6. Example Uses

6.1. Topology Diagrams

The following topology diagram shows how to connect Svc::DpWriter to a DpManager component and a processor component. The diagrams use the following instances:

• dpManager: An instance of Svc::DpManager.
• dpProcessor: A component that processes data product containers.
• dpWriter: An instance of Svc::DpWriter.
• producer: A component that produces data products.

6.2. Sequence Diagrams

The following diagram shows what happens when a buffer is sent to DpWriter, is processed, and is written to disk.

sequenceDiagram
    activate producer
    activate dpManager
    activate dpWriter
    producer-)dpManager: Send buffer
    dpManager-)dpWriter: Send buffer [bufferSendIn]
    dpWriter->>dpProcessor: Process buffer B [procBufferSendOut]
    dpProcessor-->>dpWriter: Return
    dpWriter->>dpWriter: Write B to disk
    dpWriter->>bufferManager: Deallocate B [deallocBufferSendOut]
    bufferManager-->>dpWriter: Return
    deactivate dpWriter
    deactivate dpManager
    deactivate producer