Packets objects
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Contents
1 Introduction
What: Managing packets content.
This library is a copy of the base software made by David Decotigny still available in the CVS's svn/calice/online-sw/trunk/daq/calice_packets/ directory. It is now copied at:
- libLDA/include/packets/
- libLDA/packets/
From svn/calice/online-sw/trunk/daq/calice_packets/calice_packets.hpp we can read:
* Base class. Defines the notions of SDU and PDU common to all the * accessor objects. * * Typical topology of a SDU (aka. packet): * * +-----------+--...-------...-----+--------+ * | Header | PDU | Footer | * +-----------+--...-------...-----+--------+ * * The PktAccessor_Base class defines the access to the SDU and PDU * and allows to process the packet before it is actually sent. The * children classes would alow to access the various fields inside * the Header and Footer, and manipulate the packet attributes such * as the PDU size.
All the accessor objects inherit from the PktAccessor_Base ABC,
which defines 2 notions: the SDU (Service Data Unit) and the PDU
(Protocol Data Unit). The idea is that the whole packet is called
the "SDU". It encapsulates a unique PDU, this PDU corresponding to
the arbitrary data being transmitted by the packet. So packet=SDU,
and data_carried_by_the_packet=PDU. The SDU is supposed to contain
protocol data which have to be updated once the packet is ready to
be sent, such as a CRC: the PktAccessor_Base interface declares the
sync_crc() method to do just that.
2 API
2.1 PktAccessor_Base
class PktAccessor_Base
{
public:
virtual ~PktAccessor_Base() { }
virtual void * get_sdu() const =0;
virtual unsigned int get_sdu_nbytes() const =0;
virtual void * get_pdu() const =0;
virtual unsigned int get_pdu_nbytes() const =0;
virtual void sync_crc() =0;
protected:
PktAccessor_Base() { }
};
2.2 PktAccessor_LDA_pkt
class PktAccessor_LDA_pkt
: public PktAccessor_ODR_pkt
{
public:
PktAccessor_LDA_pkt();
PktAccessor_LDA_pkt(void const* sdu,
unsigned int sdu_nbytes,
bool sdu_is_garbage = false);
PktAccessor_LDA_pkt(unsigned int min_pdu_nbytes);
virtual void attach(void const* sdu,
unsigned int sdu_nbytes,
bool sdu_is_garbage = false); /* throw() */
virtual void detach();
virtual void * get_pdu() const;
virtual unsigned int get_pdu_nbytes() const;
virtual void set_pdu_nbytes(unsigned int min_pdu_nbytes);
inline bool is_fast_command_request() const;
/* Normal packets: */
inline unsigned char get_LDA_subsystem() const;
inline void set_LDA_subsystem(unsigned char);
inline unsigned char get_LDA_optype() const;
inline void set_LDA_optype(unsigned char);
/* Same fields */
inline unsigned short get_LDA_Modifier() const;
inline void set_LDA_Modifier(unsigned short);
inline unsigned short get_LDA_from_diflink_id() const; /* base 1 */
inline void set_LDA_from_diflink_id(unsigned short /* base 1 */);
inline unsigned short get_LDA_to_diflink_id() const; /* base 0 */
inline void set_LDA_to_diflink_id(unsigned short /* base 0 */);
inline unsigned short get_LDA_PktID() const;
inline void set_LDA_PktID(unsigned short);
inline unsigned short get_LDA_DataLength() const;
inline void set_LDA_DataLength(unsigned short);
/* Fast-command packets: */
void init_LDA_FastCommand(unsigned short dif_mask,
unsigned char comma,
unsigned char data);
inline bool unpack_LDA_FastCommand(unsigned short /*out*/& cmdw /*0xfa57*/,
unsigned short /*out*/& dif_mask,
unsigned char /*out*/& comma,
unsigned char /*out*/& data) const;
private:
struct LDA_pkt * _pkt;
unsigned int _pdu_nbytes; // Related to ODR::_pdu_nbytes
uint16_t _compute_FC_parity() const; // Host byte order
PktAccessor_LDA_pkt(PktAccessor_LDA_pkt const&); // Not implemented
};
2.3 PktAccessor_DIF_pkt_block_transfer
class PktAccessor_DIF_pkt_block_transfer
: public virtual PktAccessor_Base
{
public:
PktAccessor_DIF_pkt_block_transfer(void const* sdu,
unsigned int buff_nbytes,
bool buff_is_garbage = false,
bool check_crc_ignore_dcc_nibble=false);
explicit PktAccessor_DIF_pkt_block_transfer(unsigned int pdu_nbytes);
virtual void * get_sdu() const;
virtual unsigned int get_sdu_nbytes() const;
virtual void * get_pdu() const;
virtual unsigned int get_pdu_nbytes() const;
virtual void sync_crc();
inline unsigned short get_packettype() const;
inline void set_packettype(unsigned short);
inline unsigned short get_dcc_nibble() const;
inline void set_dcc_nibble(unsigned short dcc_nibble);
inline unsigned short get_pktID() const;
inline void set_pktID(unsigned short);
inline unsigned short get_type_modifier() const;
inline void set_type_modifier(unsigned short);
inline unsigned short get_data_length() const; // Number of 16b-words
virtual void set_data_length(unsigned short num_16b_words);
private:
struct DIF_pkt_block_transfer * _pkt;
const unsigned int _buff_nbytes; // Allocated mem size (FIXED)
unsigned int _sdu_nbytes; // Related to _pdu_nbytes
unsigned int _pdu_nbytes; // Related to _sdu_nbytes
};
3 Compilation
3.1 Flags
There is two pre-compilation flags:
- CHECK_DIF_CRC: make the libLDA checking the CRC.
Note: This will slow the DAQ acquisition and may imply data lost. - DIF_FIRMWARE: make the libLDA compatible with both ECAL and DHCAL.
/include/packets/all.hh:
/* Check DIF CRC or not (faster) */ #define CHECK_DIF_CRC 0 /* Firmware version we use */ #define DIF_FIRMWARE DHCAL_v20
3.2 Ubuntu
# aptitude install g++ flex bison libboost-dev $ make $ make tests
3.3 SLC 5.5
# yum install gcc-c++ boost-devel Installing : libstdc++-devel Installing : kernel-headers Installing : glibc-headers Installing : glibc-devel Installing : gcc Installing : gcc-c++ Installing : libicu Installing : boost Installing : boost-devel $ cd ~/libLDA/packets $ make $ make tests
3.4 Gcc flag used
It seems to me that these flags are not needed, as I didn't mention diference with or without.
-fno-strict-aliasing:
Allow the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and C++), this activates optimizations based on the type of expressions.
-pipe:
Use pipes rather than temporary files for communication between the various stages of compilation. This fails to work on some systems where the assembler is unable to read from a pipe; but the GNU assembler has no trouble.
-fomit-frame-pointer:
Don't keep the frame pointer in a register for functions that don't need one. This avoids the instructions to save, set up and restore frame pointers; it also makes an extra register available in many functions. It also makes debugging impossible on some machines.
-fno-delete-null-pointer-check
Use global dataflow analysis to identify and eliminate useless checks for null pointers. The compiler assumes that dereferencing a null pointer would have halted the program. If a pointer is checked after it has already been dereferenced, it cannot be null. In some environments, this assumption is not true, and programs can safely dereference null pointers. Use -fno-delete-null-pointer-checks to disable this optimization for programs which depend on that behavior.
4 Unitary tests
Here we can test the CRC computation of packet.
This unit test is optimized for copy/past from the tcpdump output (where DIF bytes are inversed).
$ libLDA/src/packets/computeCrc 1234 crc= 0xd219 5678 crc= 0xe70b ^C
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