struct ff_envelope — generic force-feedback effect envelope
struct ff_envelope { __u16 attack_length; __u16 attack_level; __u16 fade_length; __u16 fade_level; };
duration of the attack (ms)
level at the beginning of the attack
duration of fade (ms)
level at the end of fade
The attack_level and fade_level are absolute values; when applying envelope force-feedback core will convert to positive/negative value based on polarity of the default level of the effect. Valid range for the attack and fade levels is 0x0000 - 0x7fff