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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.
    1. If a notification port is connected, then send out a notification that the write occurred. An instance of `Svc::DpCatalog` can receive this notification and use it to update the data product catalog.

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::DpWriter shall provide a port for notifying other components that data products have been written. This requirement allows Svc::DpCatalog or a similar component to update its catalog in real time. Unit Test
SVC-DPWRITER-006 Svc::DpManager shall provide telemetry that reports the number of buffers received, the number of data products written, the number of bytes written, the number of failed writes, and the number of errors. 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 dpWrittenOut DpWritten Port for sending DpWritten notifications
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

  1. The configuration constant DpWriterNumProcPorts specifies the number of ports for connecting components that perform processing.
  1. The configuration DP_FILENAME_FORMAT specifies the file name format.

3.5. Runtime Setup

You can call the configure function to supply the DP file name prefix. This is the prefix used when constructing names of files to write. For more information about the file name format, see the File Format section.

If you do not call the configure function, then the default DP file name prefix is the empty string.

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. If not, emit a warning event.
  1. If the previous step succeeded, then check that the size of B is large enough to hold a data product container packet. If not, emit a warning event.
  1. If the previous steps succeeded, then check that the packet header of B can be successfully deserialized. If not, emit a warning event.
  1. If the previous steps succeeded, then check that the header hash of B is valid. If not, emit a warning event.
  1. If the previous steps succeeded, then check that the data size recorded in the packet header fits within the buffer. If not, emit a warning event.
  1. If the previous steps succeeded, then
    1. Read the ProcType field out of the container header stored in the memory pointed to by B. Let the resulting bit mask be M.
    1. Visit the port numbers of procBufferSendOut in order. For each port number N, if N is set in M, 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. If the file write succeeded and dpWrittenOut is connected, then send the file name, priority, and file size out on dpWrittenOut.
  1. If B is valid, then 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 is formatted with the configurable format string DP_FILENAME_FORMAT. The format string must contain format specifications for the following arguments, in order.

Format Specifier Type
The DP file name prefix s
Container ID PRI_FwDpIdType
Time seconds PRI_u32
Time microseconds PRI_u32

The exact meaning of the DP file name prefix depends on the format string. Typically it is a directory path prefix.

5. Ground Interface

5.1. Commands

Kind Name Description
async CLEAR_EVENT_THROTTLE Clear event throttling

5.2. Telemetry

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

5.3. Events

Name Severity Description
BufferInvalid warning high Incoming buffer is invalid
BufferTooSmall warning high Incoming buffer is too small to hold a data product container
InvalidPacketDescriptor warning high Incoming buffer has an invalid packet descriptor
FileOpenError warning high An error occurred when opening a file
FileWriteError warning high An error occurred when writing to a file

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