SLLSFB2 April 2020 TUSB1146
PRODUCTION DATA.
The Fast AEQ mode is used to distinguish two channels (short channel and a long channel) and choose the appropriate receiver equalization setting for that channel. Because Fast AEQ only distinguishes between two choices, the AEQ time is a lot shorter than Full AEQ mode which minimizes impact to USB link training.
When Fast AEQ is enabled and channel is determined to be short, the TUSB1146 will use the value programmed into the EQx_SEL, where x = 1 or 2. If the TUSB1146 determines channel is not short, the TUSB1146 will switch to EQ value programmed into LONG_EQx register, where x = 1 or 2. During initial system evaluation, it is recommended to perform both short and long channel USB3.1 RX JTOL Gen2 testing and program EQx_SEL and LONG_EQx to the value which produced the best results for each channel configuration.
The TUSB1146 will determine short and long based on the estimate eye height. The value programmed into FASTAEQ_LIMITS register will determine the eye height limits. Software can change the defaults of this register to lower or raise the limits.
NOTE
EQ_OVERRIDE field must be set for values programmed into EQx_SEL and LONG_EQx to be used.
It is recommended to change the FASTAEQ_LIMITS register from the default value to 0x2 (80mV).