EDT, Inc.
2019 April 29
34
VisionLink F-series
Appendix C: Timestamping
Table 9
shows the structure elements of the IRIG2 footer.
Table 9. Elements of IRIG2 Footer
Element
Offset
Size
Type
Notes
Magic
0
4
u_int
This should be ASCII “EDT” followed by 01 (or
0x45445401).
Frame
4
4
u_int
This is the frame counter, which is reset when reset_intfc bit is
cleared
–
normally at the start of acquisition.
IRIG time
8
4
One of two types:
packed raw BCD,
or Unix seconds.
Type is indicated
by a bit in the
status register.
For IRIG time, the raw format is:
6 bits seconds
6 bits minutes
5 bits hours
9 bits days
6 bits years
Unix seconds = seconds since 1/1/1970 (without leap seconds)
40 MHz count
12
4
u_int
Counts using onboard 40 MHz clock since last pulse per second
40 MHz maximum ticks
at last pulse
16
4
u_int
Counts at last pulse per second (pps).
Status
20
1
u_char
Status bits:
0
–
3 = footer type (3 = Unix seconds; 5 = IRIG BCD)
4 = has valid IRIG data
5 = is synched with pps
6 = has seen IRIG error
7 = has seen pps error
Reserved
21
3
u_char
Reserved.
Monotonic Unix time
with fractional seconds
24
8
double
This value is computed and filled in by the library after DMA.
Fractional time is the 40 MHz count divided by 40 MHz max count
