EVT 2.1 Format
EVT 2.1 is a 64-bit data format.
This format outputs events of the same polarity in groups of 32 pixel.
EVT2.1 format represents an extension to the EVT 2.0 format. Events are encoded on 64 bits and are vectorized (thus ideal for high event rate applications). It is robust and provides good decoding performances. We recommend this format for all applications requiring high bandwidth and efficient decoding.
The data transmission follows either little or big-endian format, which is determined by the sensor configuration. By default, IMX636 and GenX320 sensors transmit data in little-endian format, where the least significant byte comes first and the most significant one comes last.
In each 64-bit EVT 2.1 word, the 4 Most Significant Bits (MSB) are used to define the word type.
The following table depicts the different types of events data that can be encountered:
Event |
Description |
Value |
---|---|---|
EVT_NEG |
OFF CD event, i.e. decrease in illumination (polarity ‘0’) |
‘0000’ |
EVT_POS |
ON CD event, i.e. increase in illumination (polarity ‘1’) |
‘0001’ |
EVT_TIME_HIGH |
Timer high bits: MSB part of the events timestamp. Least Significant Bits (LSB) are attached to EVT_POS / EVT_NEG words. |
‘1000’ |
EXT_TRIGGER |
External trigger output |
‘1010’ |
OTHERS |
To be used for extensions in the event types |
‘1110’ |
Note
Other event types are reserved. Contact your event-based camera distributor if you receive EVT 2.1 words whose type is not described in this table.
Event Time Encoding
All events are timestamped with a micro-second precision. Timestamp are encoded with 34 bits, providing a rollout after: 234 μs = 4 hours and 46 minutes. In order to minimize the amount of information stored with each event, the event timestamp is encoded in two parts. Lower 6 significant bits (0..5) of the micro-second timestamp are directly encoded into the CD or Trigger event, while the 28 most significant bits (6..33) of the timestamp are stored in a dedicated EVT_TIME_HIGH event. To rebuild the full event timestamp, the lower bits of the timestamp embedded in the event must be concatenated with the last EVT_TIME_HIGH event information.
To compute the full resolution of the timestamp, decoding of the event stream should start after receiving the first event of type EVT_TIME_HIGH.
EVT_NEG
Bit Range |
Bit Width |
Field Name |
Description |
Default Value |
---|---|---|---|---|
63..60 |
4 bits |
type |
Event type | EVT_NEG (‘0000’) |
‘0000’ |
59..54 |
6 bits |
timestamp |
Least significant bits of the event time base |
– |
53..43 |
11 bits |
x |
Pixel X coordinate aligned on 32 |
– |
42..32 |
11 bits |
y |
Pixel Y coordinate |
– |
31..0 |
32 bits |
valid |
Set bits represent valid events at coordinates:
|
– |
Note
Polarity of EVT_NEG events is implicitly 0, encoding a decrease of illumination.
EVT_POS
Bit Range |
Bit Width |
Field Name |
Description |
Default Value |
---|---|---|---|---|
63..60 |
4 bits |
type |
Event type | EVT_POS (‘0001’) |
‘0001’ |
59..54 |
6 bits |
timestamp |
Least significant bits of the event time base |
– |
53..43 |
11 bits |
x |
Pixel X coordinate aligned on 32 |
– |
42..32 |
11 bits |
y |
Pixel Y coordinate |
– |
31..0 |
32 bits |
valid |
Set bits represent valid events at coordinates:
|
– |
Note
Polarity of EVT_POS events is implicitly 1, encoding an increase of illumination.
EVT_TIME_HIGH
Bit Range |
Bit Width |
Field Name |
Description |
Default Value |
---|---|---|---|---|
63..60 |
4 bits |
type |
Event type | EVT_TIME_HIGH |
‘1000’ |
59..32 |
28 bits |
timestamp |
Most significant bits of the event time base |
– |
31..0 |
32 bits |
– |
Unused. Stuck at zero |
‘00…0’ |
EXT_TRIGGER
Bit Range |
Bit Width |
Field Name |
Description |
Default Value |
---|---|---|---|---|
63..60 |
4 bits |
type |
Event type | EXT_TRIGGER |
‘1010’ |
59..54 |
6 bits |
timestamp |
Least significant bits of the event time base |
– |
53..45 |
9 bits |
– |
Unused. Stuck at zero |
‘0’ |
44..40 |
5 bits |
id |
Trigger channel ID
|
– |
39..33 |
7 bits |
– |
Unused. Stuck at zero |
‘0’ |
32 |
1 bit |
value |
Trigger current value (edge polarity): 0: falling edge 1: rising edge |
‘0’ |
31..0 |
32 bits |
– |
Unused. Stuck at zero |
‘0’ |