"CCSDS telecommand header (bytes 6-7)" (SVC/ITC)

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Focus:	Maintenance / Operation
Structures:	Abstract / Concrete

Definition:

Alignment:	2-byte boundary
APID:	720/0x2D0
Attribute(s):
C type:	unsigned short
Length:	16 bits (2 bytes)

Description:

Bitfields for bytes 6-7 of a standard CCSDS telecommand header, where a two-byte secondary header containing a function code has been defined.

Layout: (hide detail; help)

Start	Stop	Size		Item Type and Name
0	0	1		Fnc_pad fnc_pad
1	15	15		Fnc_code fnc

Hdr3 (bf)
|  Fnc_pad fnc_pad (0)
|  Fnc_code fnc (1-15)

typedef struct _ITC_Hdr3_Bfl {

    #if ENDIANNESS_IS_BIG

    /* Padding */
    unsigned short       fnc_pad:1;

    /* CCSDS telecommand function code */
    unsigned short       fnc:15;

    #elif ENDIANNESS_IS_LITTLE

    /* CCSDS telecommand function code */
    unsigned short       fnc:15;

    /* Padding */
    unsigned short       fnc_pad:1;

    #else

    #error _FILE_ ENDIANNESS NOT DEFINED

    #endif

} __attribute__((packed)) ITC_Hdr3_Bfl;

typedef union _ITC_Hdr3 {

    /* underlying unsigned short */
    unsigned short                  us;

    /* struct mapped bitfield */
    struct _ITC_Hdr3_Bfl            bf;

} ITC_Hdr3;

Fields:

Fnc_code (index)

Attribute(s):  

Brief:  "CCSDS telecommand function code"

Instance(s):  fnc

CCSDS telecommand function code

Fnc_pad (index)

Attribute(s):  

Brief:  "Padding"

Instance(s):  fnc_pad

Function codes are not allowed to touch the most significnat bit of the 16-bit function code. This padding places the bit off limits.

Used by:

CmdHeader