The total width value of an entry is calculated using the following equation:
Entry Width = KEY_WIDTH +
RESPONSE_WIDTH + PRIORITY_WIDTH + CTRL
The control bits correspond
to a single bit for the fixed rate STCAM and up to (11 + total range width) for the
variable rate STCAM to the entry width. To access the whole entry in parallel several
block RAMs or URAMs are used. Block RAM and URAM are allocated in data width increments
of 64 bits. To avoid quantification losses, it is beneficial if the entry size is close
below or on a 64-bit boundary. For example, if the Entry Width is 308 bits, the
quantification loss is only 12 bits per entry: 5*64 -
308 = 12.
The maximum supported entry width is 2048 bits.
For LPM mode, the maximum supported entry width is 512 bits, and the width of an entry is calculated using the following equation:
Entry Width = KEY_WIDTH + 8 * RESPONSE_WIDTH
+ CTRL
The number of control bits is between 32 and 63. CTRL is 32 bits for a single-bit prefix field and 63 bits for a 128-bit wide prefix field. In all other aspects, the quantification works as described previously.