Clocking - Clocking - 1.0 English - PG276

There are three clock types that must be provided to the HBM core:

• The HBM_REF_CLK_x drives a PLL which then generates a clock for the eight memory controllers, as well as the memory clock for the HBM stack. There is one PLL per HBM stack. This clock must be sourced from a MMCM/BUFG, or from a BUFG. The HBM_REF_CLK_x can be sourced from the cascading clocking sources derived from another clock. The source clock for this derived clock must come from a GCIO pin within the same SLR as the HBM. The clock generator driving the GCIO needs to have jitter less than 3 pS RMS.
• The APB_x_PCLK is used for the APB register port access. This can be asynchronous to the other clocks. There is one APB clock port per HBM stack. The APB_x_PCLK can be sourced from the cascading clocking source or MMCM or GCIO pin.
• The AXI_xx_ACLK is the clock for each of the AXI ports. These can be asynchronous to the other clocks. The AXI_xx_ACLK can be sourced from the cascading clocking source or MMCM or GCIO pins.

The global routing switch does not have a separate clock input, but rather shares one of the AXI_xx_ACLKs. This is automatically selected by the software to be one of the clocks in the middle of the user-selected memory controllers. This can be checked by looking at the hbm_0.v file. There are parameters, CLK_SEL_xx, and only one has the attribute TRUE.

For maximum efficiency, it is important that the AXI clock selected is the highest frequency of all of the AXI port clocks.