Classification
Revision
Public
PA6
Document Number
Date
17-1957
2018-06-07
4.6
Data Struct
The ADQ7-FWATD data struct is used to represent a record in user space and is used by all FWATD-
specific functions associated with handling data. The struct offers an intuitive abstraction of all parts
which together constitute a record: the metadata fields as well as the actual waveform data.
The struct is 32 B (after padding) and consists of the fields presented in Tab.
4
where the first table
entry starts at byte zero.
Table 4: Contents of the ADQ7-FWATD data struct.
Field name
Type
Description
Timestamp
uint64_t
The time stamp of the first raw record in the ba-
tch.
Data
int32_t *
Pointer to memory where the record data is lo-
cated.
RecordNumber
uint32_t
The record number.
Status
uint32_t
System status at the point where the record was
collected. See Section
4.7.2
for details.
RecordsAccumulated
uint32_t
Number of accumulated records reflected in the
data.
Channel
uint8_t
The originating channel.
4.7
Robustness
To this end, ADQ7-FWATD features a data discarding mechanism to deal with the many different types
of overflow that may occur. The core concept is to discard data in a well-defined manner such that the
overall accumulation grid is preserved and corrupted records are prevented from propagating to the user
space.
The digitizer firmware is engineered as a well-balanced system, meaning no overflows can occur
due to internal effects. The first and most critical point in the system where overflows can occur is the
device-to-host interface, which connects the digitizer to the host computer. This connection is beyond the
complete control of the digitizer and determines the effective data transfer rate which directly translates to
the limits of the WFA settings. The digitizer on its own is a real-time system, but once the host computer
is included in the system view, this is no longer true as it is at the discretion of the operating system to
deliver the data to the user application.
Note
The most critical point is the device-to-host interface. The maximum data transfer rate translates into
the limits of the WFA settings.
The second critical point in the system is the queue interface which provides the user with accumulated
records as long as there is available memory. If there is no free memory to place the newly transferred
data, the data flow will stall and eventually cause data to be discarded.
ADQ7-FWATD User Guide
www.teledyne-spdevices.com
Page 12 of 26
