F´ Flight Software - C/C++ Documentation  devel
A framework for building embedded system applications to NASA flight quality standards.
Svc::AMPCSSequence Class

Svc::AMPCSSequence Class

AMPCSSequence is a derived class of CmdSequencer::Sequence. It loads, validates, and runs AMPCS-compatible sequence files.

1 File Format

A sequence file consists of a 32-bit sequence header followed by up to 32,768 bytes of record data.

The record data consists of zero or more records. Each record has the following format:

Record Field Size in Bytes Description
Time Flag 1 Either 0x0 denoting absolute time or 0xFF denoting relative time
Time 4 The time in seconds
CMD Length 2 The size in bytes of the Command field
Command < 1017 A serialized command in F Prime format, with a 16-bit opcode

2 Implementation

The AMPCSSequence class implements the virtual functions of CmdSequencer::Sequence as follows.

2.1 <tt>loadFile(</tt>*filename*<tt>)</tt>

  1. Read the stored CRC value from filename.CRC32.
  2. Ask the OS for the size of the sequence file, and use it to compute the size of the command record data.
  3. Read the 32-bit sequence header.
  4. Read the command record data into a serial buffer B.
  5. Check that the format of the records is valid according to the binary format specified in File Format.
  6. Compute the CRC value of the binary file and check it against the stored value.
  7. Fill in m_header as follows:
    • m_fileSize: The size of the command record data, computed in item 2 above.
    • m_numRecords: Count the records when validating them.
    • m_timeBase: Use 0xFFFF (don't care).
    • m_timeContext: Use 0xFF (don't care).

2.2 <tt>hasMoreRecords</tt>

Return true if and only if B has more data.

2.3 <tt>nextRecord</tt>

Deserialize and return the next record stored in the serial buffer. The deserialized record contains the following binary data in its argument field:

Field Size in Bytes Value
Packet Descriptor 4 Fw::ComPacket::FW_PACKET_COMMAND
Opcode 4 The opcode stored in bytes 0-1 of the serial record, zero-extended to four bytes
Arguments Variable Bytes 2-end of the serial record

2.4 <tt>reset</tt>

Reset B for deserialization.

2.5 <tt>clear</tt>

Reset B for serialization.