Clocking in GTZ
The clocking scheme in GTZ is different from clocking schemes in other GTs. The basis of USRCLK routing is vertical GCLK spines that run through multiple SLRs (depending on the device size).
There are a total of 32 vertical GCLK lines available in GTZ, with up to 16 GTZ channels in which 8 GTZ channels are located on the North GTZ die, and the other 8 GTZ channels on South die. The vertical GCLK line that drives TXUSRCLK or RXUSRCLK clock inputs to both GTZ dies need to be shared between the 16 GTZ channels.
GCLK Spines
Table 1 below shows the assignment of vertical GCLK lines to GTZ clocks.
GCLK spine # / GTZ North / GTZ South / Direction at GTZ die0 / TXOUTCLK0 / NC / Output
1 / TXUSRCLK0 / TXUSRCLK4 / Input
2 / TXOUTCLK1 / NC / Output
3 / TXUSRCLK1 / TXUSRCLK5 / Input
4 / TXUSRCLK2 / TXUSRCLK6 / Input
5 / TXUSRCLK3 / TXUSRCLK7 / Input
6 / RXOUTCLK0 / NC / Output
7 / RXUSRCLK0 / RXUSRCLK4 / Input
8 / RXOUTCLK1 / NC / Output
9 / RXUSRCLK1 / RXUSRCLK5 / Input
10 / RXOUTCLK2 / NC / Output
11 / RXUSRCLK2 / RXUSRCLK6 / Input
12 / RXOUTCLK3 / NC / Output
13 / RXUSRCLK3 / RXUSRCLK7 / Input
14 / DRPCLK0 / DRPCLK1 / Input
15 / CFGCLK / CFGCLK / Input
16 / Unused / Unused / Input
17 / DRPCLK1 / DRPCLK0 / Input
18 / RXUSRCLK7 / RXUSRCLK3 / Input
19 / NC / RXOUTCLK3 / Output
20 / RXUSRCLK6 / RXUSRCLK2 / Input
21 / NC / RXOUTCLK2 / Output
22 / RXUSRCLK5 / RXUSRCLK1 / Input
23 / NC / RXOUTCLK1 / Output
24 / RXUSRCLK4 / RXUSRCLK0 / Input
25 / NC / RXOUTCLK0 / Output
26 / TXUSRCLK7 / TXUSRCLK3 / Input
27 / TXUSRCLK6 / TXUSRCLK2 / Input
28 / TXUSRCLK5 / TXUSRCLK1 / Input
29 / NC / TXOUTCLK1 / Output
30 / TXUSRCLK4 / TXUSRCLK0 / Input
31 / NC / TXOUTCLK0 / Output
Table 1: GCLK Spine assignments
The OUTCLKs are marked in red to show they need to be routed to either BUFG_LB or BUFGCTRL to be used as USRCLKs.
Figure 1 below shows the high level view of GCLK spines.
Figure 1: GCLK Spines
Resources required
The OUTCLK/MMCM clock can be used as usrclk only via either BUFG_LB(only for OUTCLK) or BUFGCTRL. The diagrams below are in the 7 Series GTZ User Guide UG478 in the GTZ lounge.
Figure 2: User Clock routing
BUFGCTRL
Each GCLK spine is sub divided in segments to allow user some flexibility. The following figure is a representation of XC7VH870T device SLRs and GTZs. Each column represents the USRCLK spine with possible BUFGCTRLs location.
Figure 3: BUFGCTRL locations
The selection of BUFGCTRL is based on the usage. Zooming into column1 (TXUSRCLK0 on North and TXUSRCLK4 on south) the diagram looks like the figure below:
Figure 4: Zooming in one of the USRCLK spine
Depending on the logic/MMCM placement an appropriate BUFGCTRL has to be used. If MMCM is near south Octal then BUFGCTRL_X0Y1 has to be used, if in the middle SLR BUFGCTRL_X0Y33 and BUFGCTRL_X0Y65 if near north octal.
Figures below show the scenarios the clock can be routed and the spine can be segmented.
Figure 5: Routing scenarios
Fig A – Unrouted spine with 3 BUFGCTRLs
Fig B – MMCM/logic place near south octal uses bottom BUFGCTRL and MMCM/logic placed near north octal uses top BUFGCTRL. The BUFGCTRL in the middle is unused.
Fig C – Center BUFG clocks the top octal and bottom BUFG clocks the south.
Fig D, E, F and G are similar with different scenarios.