Ticks
The USB Timing Box operates on a 0.28ppm time base, counting 256 ticks per second.
Time Stamps
The USB Timing Box does not know the true date and time. It does not know about leap days or seconds. It has no built-in calendar. All times are internally stored as 32 bit time stamps with 256th of a second resolution. As stored passings can be up to 24 hours old. On startup, the USB Timing Box time stamp starts running from 24 hours worth of ticks to avoid negative passing time stamp values.
Computer Time Reference - EPOCHREF
In order to translate a passing time stamp to a real world computer time, you need to reference the internal time base to your computer time. At the point in time you call EPOCHREFSET and pull the DTR-Line HIGH, you create a synchronized value pair:
ref_time_stamp @ ref_computer_time
Where ref_time_stamp is the internal USB Timing Box time base value at synchronization and ref_computer_time is a value set by your application. Both values are stored as a pair in the USB Timing Box. You can always read this value pair with EPOCHREFGET. If your software or computer crashes, the USB Timing Box will keep the correct event time for you. To convert a pass_time_stamp to a real world computer time, you must calculate:
Computer_Time(pass_time_stamp) =
ref_computer_time + ((pass_time_stamp - ref_time_stamp) / 256.0)
RACE RESULT strongly recommends using the standard UNIX TIME for your computer time reference value. https://en.wikipedia.org/wiki/Unix_time
| Unix Time Epoch | USB Timing Box Time Stamp (FW 2.5 and below) | USB Timing Box Time Stamp (FW 2.6 and up after <CONFSET;B3;1>) | |
| Data | 32bit | 32bit | 40bit |
| Start | 1. Jan 1970 | Last USB Timing Box start up / reset | Last USB Timing Box start up / reset + 7 days |
| Resolution | 1 second | 256th of a second | 2048th of a second |
| Overflow | 19. Jan 2038 | after 193 days of operation | 2^40 / (2048*3600*24*365) = 17 years |
| Init value | 0 | 24*3600*256 = 22.118.400 (24h) | 7*24*3600*2048 = 1.238.630.400 (7 days) |