2.6 Clock Sources: On-Chip Oscillators, PLLs, and CCCs

IGLOO 2 devices have two on-chip RC oscillators—a 1 MHz RC oscillator and a 50 MHz RC oscillator—and the main crystal oscillator (32 KHz–20 MHz). These are available to the user for generating clocks to the on-chip resources and the logic built on the FPGA fabric array. These oscillators can be used in conjunction with the integrated user PLLs and FAB_CCCs to generate clocks of varying frequency and phase. In addition to being available to the user, these oscillators are also used by the system controller, Power-on Reset circuitry, and HPMS during the Flash*Freeze mode.

IGLOO 2 devices have up to eight fabric CCC (FAB_CCC) blocks and a dedicated PLL associated with each CCC to provide flexible clocking to the FPGA fabric portion of the device. The user has the freedom to use any of the eight PLLs and CCCs to generate the fabric clocks and the internal HPMS clock from the base fabric clock (CLK_BASE). There is also a dedicated CCC block for the HPMS (HPMS_CCC) and an associated PLL (MPLL) for HPMS clocking and de-skewing the CLK_BASE clock. Fabric Alignment Clock Controller (FACC), part of the HPMS CCC, is responsible for generating various aligned clocks required by the HPMS for correct operation of the HPMS blocks and synchronous communication with the user logic in the FPGA fabric.