GEM Clocks

Versal ACAP Technical Reference Manual (AM011)

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1.4 English

The GEM controller includes several types of clocks.

  • Main reference clock
  • Timestamp unit clock
  • LPD IOP switch clock

The clocks are illustrated in the Block Diagram section.

Clock frequency guidelines are included in the I/O Peripheral Clock Frequency Requirements section.

Main Reference Clock

The GEMx_REF_CLK clocks from the LPD clock controller are programmed by the LPD_IOP_SLCR GEM_Clk_Ctrl register.

    • GEM0_REF_CLK
    • GEM1_REF_CLK

GEM_TX Clock

The GEM_TX clock has a couple of sources. The frequency and accuracy is defined by the Ethernet 802.3 specification.

Timestamp Unit Clock

The timestamp unit (TSU) clocking is more complicated, and is shown in the figure in the Block Diagram section and explained in the Precision Timestamp Unit section.

LPD IOP Switch Clock

The APB programming interface and the AXI DMA controller interface are clocked by the LPD_IOPSW_CLK clock. This clock is controlled by the LPD clock controller using the CRL.LPD_IOPSW_CTRL register.