3.3.3.3. Peripheral Clock Group

Cyclone® V Hard Processor System Technical Reference Manual

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Date 8/28/2023

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3.3.3.3. Peripheral Clock Group

The peripheral clock group consists of a PLL, dividers, and clock gating. The clocks in the peripheral clock group are derived from the peripheral PLL. The peripheral PLL can be programmed to be sourced from the HPS_CLK1 pin, the HPS_CLK2 pin, or the f2h_periph_ref_clk clock provided by the FPGA fabric.

The FPGA fabric must be configured with an image that provides the f2h_periph_ref_clk before selecting it as the clock source. If the FPGA must be reconfigured and f2h_periph_ref_clk is being used by modules in the HPS, an alternate clock source must be selected prior to reconfiguring the FPGA.

Clocks that always use the peripheral PLL output clocks as the clocks source are:

emac0_clk
emac1_clk
usb_mp_clk
spi_m_clk
can0_clk
can1_clk
gpio_db_clk
h2f_user1_clk

In addition, clocks that may use the peripheral PLL output clocks as the clock source are:

sdmmc_clk
nand_clk
qspi_clk
l4_mp_clk
l4_sp_clk

The counter outputs from the main PLL can have their frequency further divided by external dividers. Transitions to a different divide value occur on the fastest output clock, one clock cycle prior to the slowest clock’s rising edge. For example, the clock transitions on cycle 15 of the divide‑by‑16 divider for the main C2 output and cycle 3 of the divide‑by‑4 divider for the C1 output.

Table 11. Peripheral PLL Output Assignments
PLL	Output Counter	Clock Name	Frequency	Phase Shift Control
Peripheral	C0	emac0_base_clk	Up to 250 MHz	No
	C1	emac1_base_clk	Up to 250 MHz	No
	C2	periph_qspi_base_clk	Up to 432 MHz	No
	C3	periph_nand_sdmmc_base_clk	Up to 250 MHz for the NAND flash controller and up to 200 MHz for the SD/MMC controller	No
	C4	periph_base_base_clk	Up to 240 MHz for the SPI masters and up to 200 MHz for the scan manager	No
	C5	h2f_user1_base_clk	`osc1_clk` to 100 MHz	No

The following figure shows programmable post-PLL dividers and clock gating for the peripheral clock group. Clock gate blocks in the diagram indicate clocks that may be gated off under software control. Software is expected to gate these clocks off prior to changing any PLL or divider settings that might create incorrect behavior on these clocks.

Figure 7. Peripheral Clock Group Divide and Gating

Table 12. Peripheral Clock Group Clocks
System Clock Name	Frequency	Divided From	Constraints and Notes
usb_mp_clk	Up to 200 MHz	Peripheral PLL C4	Clock for USB
spi_m_clk	Up to 240 MHz for the SPI masters and up to 200 MHz for the scan manager	Peripheral PLL C4	Clock for L4 SPI master bus and scan manager
emac0_clk	Up to 250 MHz	Peripheral PLL C0	EMAC0 clock. The 250 MHz clock is divided internally by the EMAC into the typical 125/25/2.5 MHz speeds for 1000/100/10 Mbps operation.
emac1_clk	Up to 250 MHz	Peripheral PLL C1	EMAC1 clock The 250 MHz clock is divided internally by the EMAC into the typical 125/25/2.5 MHz speeds for 1000/100/10 Mbps operation.
l4_mp_clk	Up to 100 MHz	Main PLL C1 or peripheral PLL C4	Clock for L4 master peripheral bus
l4_sp_clk	Up to 100 MHz	Main PLL C1 or peripheral PLL C4	Clock for L4 slave peripheral bus
can0_clk	Up to 100 MHz	Peripheral PLL C4	Controller area network (CAN) controller 0 clock
can1_clk	Up to 100 MHz	Peripheral PLL C4	CAN controller 1 clock
gpio_db_clk	Up to 1 MHz	Peripheral PLL C4	Used to debounce GPIO0, GPIO1, and GPIO2
h2f_user1_clock	Peripheral PLL C5	Peripheral PLL C5	Auxiliary user clock to the FPGA fabric

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3.3.3.3. Peripheral Clock Group