Safe Timing Clocking Topologies for MMCM and XPLL

Versal ACAP Clocking Resources Architecture Manual (AM003)

Document ID
AM003
Release Date
2022-05-24
Revision
1.4 English

The following tables document the netlist topologies and clock managers settings for MMCM and XPLL with two sets of PDs that must be followed to ensure that CLKIN/CLKOUTx and different CLKOUTx can be timed safely.

Use the following convention to interpret the conditions in the subsequent tables.

Conditional
It is safe to time the signals of interest only if the condition specified in the header is met. Known skew indicates that the timing between the signals of interest can be calculated by the timer.
N/A
It is always safe to time the signals of interest regardless of the condition in the header.
Table 1. CLKOUTx Settings that Allow for Safe Timing with CLKIN
CLKOUTx_PHASE_CTRL Known Skew CLKIN→CLKIN1_DESKEW Known Skew CLKIN→CLKIN2_DESKEW Known Skew CLKIN1_DESKEW→CLKIN2_DESKEW Info Only: Phase Shift Controlled By
00 N/A N/A N/A Fixed phase, no deskew
10 N/A N/A N/A Phase shift interface 1
01 Conditional N/A N/A PD1
11 N/A Conditional N/A PD2
  1. Timing based on initial phase, same as CLKOUTx_PHASE_CTRL=00.
Table 2. CLKOUTx Settings that Allow for Safe Timing with CLKOUTy (CLKOUTy_PHASE_CTRL=00 or 10)
CLKOUTx_PHASE_CTRL Known Skew CLKIN→CLKIN1_DESKEW Known Skew CLKIN→CLKIN2_DESKEW Known Skew CLKIN1_DESKEW→CLKIN2_DESKEW Info Only: Phase Shift Controlled By
00 N/A N/A N/A Fixed phase, no deskew
10 N/A N/A N/A Phase shift interface 1
01 Conditional N/A N/A PD1
11 N/A Conditional N/A PD2
  1. Timing based on initial phase, same as CLKOUTx_PHASE_CTRL=00.
Table 3. CLKOUTx Settings that Allow for Safe Timing with CLKOUTy (CLKOUTy_PHASE_CTRL=01)
CLKOUTx_PHASE_CTRL Known Skew CLKIN→CLKIN1_DESKEW Known Skew CLKIN→CLKIN2_DESKEW Known Skew CLKIN1_DESKEW→CLKIN2_DESKEW Info Only: Phase Shift Controlled By
00 Conditional N/A N/A Fixed phase, no deskew
10 Conditional N/A N/A Phase shift interface 1
01 N/A N/A N/A PD1 2
11 N/A N/A Conditional PD2
  1. Timing based on initial phase, same as CLKOUTx_PHASE_CTRL=00.
  2. Both CLKOUTx and CLKOUTy must have the same frequency which is equivalent to having the same CLKOUTx_DIVIDE setting. For more information, see Functioning of Deskew.
Table 4. CLKOUTx Settings that Allow for Safe Timing with CLKOUTy (CLKOUTy_PHASE_CTRL=11)
CLKOUTx_PHASE_CTRL Known Skew CLKIN→CLKIN1_DESKEW Known Skew CLKIN→CLKIN2_DESKEW Known Skew CLKIN1_DESKEW→CLKIN2_DESKEW Info Only: Phase Shift Controlled By
00 N/A Conditional N/A Fixed phase, no deskew
10 N/A Conditional N/A Phase shift interface 1
01 N/A N/A Conditional PD1
11 N/A N/A N/A PD2 2
  1. Timing based on initial phase, same as CLKOUTx_PHASE_CTRL=00.
  2. Both CLKOUTx and CLKOUTy must have the same frequency which is equivalent to having the same CLKOUTx_DIVIDE setting. For more information, see Functioning of Deskew.