#include <DataFormat.h> typedef struct _RingItemHeader {uint32_t s_size;uint32_t s_type;} RingItemHeader pRingItemHeader; typedef struct _StateChangeItem {RingItemHeader s_header;uint32_t s_runNumber;uint32_t s_timeOffset;time_t s_Timestamp;char s_title[TITLE_MAXSIZE+1];} StateChangeItem, *pStateChangeItem; typedef struct _ScalerItem {RingItemHeader s_header;uint32_t s_intervalStartOffset;uint32_t s_intervalEndOffset;time_t s_timestamp;uint32_t s_scalerCount;uint32_t s_scalers[1];} ScalerItem, *pScalerItem; typedef struct _TextItem {RingItemHeader s_header;uint32_t s_timeOffset;time_t s_timestamp;uint32_t s_stringCount;char s_strings[1];} TextItem, *pTextItem; typedef struct _PhysicsEventItem {RingItemHeader s_header;uint16_t s_body[1];} PhysicsEventItem, *pPhysicsEventItem; typedef struct __PhysicsEventCountItem {RingItemHeader s_header;uint32_t s_timeOffset;time_t s_timestamp;uint64_t s_eventCount;} PhysicsEventCountItem, *pPhysicsEventCountItem;
This header describes the format of data placed in NSCL ring
buffers. Each item consists of an envelope and a payload.
The envelope,
RingItemHeader contains a size:
uint32_t s_size;
which is the total size of the item (inlcuding the header) in
bytes, and an item type
uint32_t s_type;
which indicates what the item contains. The payload immediately
follows the header and varies in structure depending on the
value in s_type.
Items are placed in rings in native machine byte ordering. While the data type is 32 bits long, only the least significant 16 bits are nonzero. This allows a determination of the endianness of the system that generated the item.
STRUCTURES below describes each of the ring items defined
at this time. CONSTANTS defines the set of values that
s_type can take (once converted to
the localh host's endian-ness).
The following ring items have been defined:
This ring item carries information about state changes in data taking its header will have a type that is one of BEGIN_RUN, END_RUN, PAUSE_RUN or RESUME_RUN depending on the state change that is being documented.
A state change has the following set of fields:
RingItemHeader s_header;
This is the ring item's header. The contents of this structure have been described in DESCRIPTION above.
uint32_t s_runNumber;
Contains the run number of the current run. When data are being recorded it is expected this will be a unique number.
uint32_t s_timeOffset;
Contains the number of seconds into the run at which this transition occured.
time_t s_Timestamp;
Contains the absolute time at which the item was initially generated. This value is the number of seconds since the Unix epoch. The various functions normally defined in <time.h> can be used to manipulate this value once it is in native byte ordering.
char s_title[TITLE_MAXSIZE+1];
Null terminated string that contains the run title. The actual character part is gauranteed to be at most TiTlE_MAXSIZE bytes ensuring that there is a terminating null byte. At this time multi-byte/wide characters are not excluded but not explicitly supported.
This item type contains incremental scaler data. NSCL scaler data by standard is incremental so that users don't have to be concerned with how scaler hardware handles overflows (assuming the scaler registers are wide enough to accomodate a single counting interval). It is the Readout program's responsibility to ensure scaler values represent incremental values.
ScalerItem ring items have the following fields:
RingItemHeader s_header;
The standard header. The
s_type field will
contain the value
INCREMENTAL_SCALERS
(see CONSTANTS below).
uint32_t s_intervalStartOffset;
The number of seconds into the run at
which this counting interval started.
If this is the first scaler item in a
run this will be
0. If not this will
be the
s_intervalEndOffset
of the previous scaler item in the run.
uint32_t s_intervalEndOffset;
The number of seconds into the run at
which this counting interval ended.
Normally this wil be the
s_intervalStartOffset
of the next incremental scaler item.
time_t s_timestamp;
The absolute time at which this scaler item was produced. This is a Unix time_t which means it is the number of seconds since the unix epoch time and date. Once converted into local host byte ordering, this value can be used in all function in <time.h> that take a time_t as a parameter.
uint32_t s_scalerCount;
Contains the number of scalers that have been read out. This is assumed to be a number of uint32_t values.
uint32_t s_scalers[1];
This is the first element of an array
of scalers. The actual size of this array
will be determined by
s_scalerCount
Several item types contain documentation data in
the form of a list of null terminated strings.
These are TextItem item types and the
actual contents are differntiated by the
s_type field of the item header.
The TextItem contains the following fields:
RingItemHeader s_header;
The standard ring item header. The
s_type field will be
either MONITORED_VARIABLES
or PACKET_TYPES. The
string formats vary depending on which of
these is used. See the s_strings
field description velow for more information.
uint32_t s_timeOffset;
The time in seconds from the beginnning of the run at which this item was emitted.
time_t s_timestamp;
A unix absolute timestamp. This is a time in seconds since the beginning of the unix epoch. Once converted to the local host byte ordering, this is a valid time_t which can be used in any of the function in <time.h>
uint32_t s_stringCount;
The number of strings in the item.
char s_strings[1];
The first byte of string storage. The
actual size of the s_strings
array depends on the number and lengths
of the strings, but can be computed from
the s_size field of the
header.
The actual format of each string depends
on the s_type field
of the header.
MONITORED_VARIABLES items contain the values of readout variables that have been chosen for monitoring. One application is the injection of EPICS process variable data into Readout's Tcl interpreter.
A string for a MONITORED_VARIABLE is a Tcl command that would recreate the variable with that value (e.g. a Tcl set command) like:
PACKET_TYPES items
are created by the
CDocumentedPacket
in the SBS readout framework. These strings
are a colon separated set of fields that
provide in order, for each packet type the
packet id, the packet description,
the packet version and the date at which
the CDocumentedPacket
object has been instantiated. For
example:
This contains data from a physics trigger.
The fields include the standard header
s_header and a
uint16_t s_body;
which is the first word of the body.
The header's s_type field
has the value PHYSICS_EVENT.
The actual size of the body depends on how many
words were read out for this event. At this level
of formatting ther is no specification describing
the payload of this item. It is customary, however
to put some information about the size of the
event read in the beginning of the event.
The structure of this size may depend on the
readout framework, however.
This item type is used to describe the number of triggers that have been recorded since the start of the run. This can be used for several applications including a determination of data fraction for sampling consumers, and raw data rate approximation.
This item has the following fields:
RingItemHeader s_header;
The standard ring item header.
The s_type field will
be PHYSICS_EVENT_COUNT.
uint32_t s_timeOffset;
The run relative time in seconds at which this item was emitted by the readout framework(s).
time_t s_timestamp;
Absolute timestamp describing when this
item was emitted. When converted to
native byte ordering, This item can be
used in e.g. ctime
and other time functions described in
<time.h>
uint64_t s_eventCount;
Number of events acquired so far this run.
DataFormat.h provides constant definitions for the possible item type values as well as other definitions:
Item type for a StateChangeItem that announces a new run is starting.
Item type for a StateChangeItem that announces a run is ending.
Item type for a StateChangeItem that announcdes a run is being paused.
Item type for a StateChangeItem that announces a paused run is being resumed.
Item type for a TextItem that contains packet type definitions.
Item type for a TextItem that contains values of variables monitored at run-time.
Item type for a ScalerItem. These contain incremental scaler readout values.
Item type for an item that contains physics data.
Item type for a PhysicsEventCountItem which contains information about how many events have been put in the ring buffer this run.
If users create application specific items the item type code should be at least this value. The largest allowed item type code is 0xffff.
The maximum number of non null characters in a title string.