Achronix Speedster22i PCIe - Manual (Page 64)

UG030, April 26, 2013 64
Field Name Default Values Description Verilog Parameter
microseconds. This is the default
value, but can be reduced to
speed up equalization if the
round trip delay is understood in
detail.
Preset - Max
Preset Addr 9 0-9 5.3.3.1 Preset Method
Step through the PCI Express
Specification-defined Tx Presets
(0 through 9).
The Preset Method can optionally
be configured to communicate the
desired Preset for the remote
device to use by Preset Number
(let the remote device convert the
Preset to the appropriate
coefficients) or by calculating the
coefficients equivalent to the
Preset Number and
communicating the coefficients to
the remote device.
When the core is configured to
communicate the Preset via
coefficients rather than Preset
Number, the core uses the
coefficients from the Pre-Cursor
Coefficient and Post-Cursor
Coefficient columns in the table
above to perform the calculation.
The coefficient target, expressed
as a real number in parenthesis, is
given along with the rounded (to
1/64) coefficient value that is
used.
The Preset method works well
with PHY which take the
maximum of 2mS to evaluate
equalization settings since there
are only 10 (the max number that
could be attempted) settings that
would typically be tried.
Typically Preset 0xA would not
be tried since it is primarily
intended for diagnostics.
The Preset method trying all
presets 0 to 9 is recommended for
users to start with if they are CFG_8G_CONSTANTS_
EQ_PRESET_ADDR_LIM
IT