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dimamali |
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Use Virtex CLKDLL for clock synchronisation
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CONFIG_CLK_INFERRED
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Certain target technologies include clock generators to scale or
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phase-adjust the system and SDRAM clocks. This is currently supported
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for Xilinx and Altera FPGAs. Depending on technology, you can select
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to use the Xilinx CKLDLL macro (Virtex, VirtexE, Spartan1/2), the
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Xilinx DCM (Virtex-2, Spartan3, Virtex-4), or the Altera ALTDLL
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(Stratix, Cyclone). Choose the 'inferred' option if you are not
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using Xilinx or Altera FPGAs.
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Using a technology specific clock generator is necessary to
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re-syncronize the SDRAM clock. For this to work, connect the
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external SDCLK signal with PLLREF.
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Clock multiplier
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CONFIG_CLK_MUL
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When using the Xilinx DCM or Altera ALTPLL, the system clock can
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be multiplied with a factor of 2 - 32, and divided by a factor of
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1 - 32. This makes it possible to generate almost any desired
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processor frequency. When using the Xilinx CLKDLL generator,
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the resulting frequency scale factor (mul/div) must be one of
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1/2, 1 or 2.
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WARNING: The resulting clock must be within the limits specified
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by the target FPGA family.
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Clock divider
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CONFIG_CLK_DIV
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When using the Xilinx DCM or Altera ALTPLL, the system clock can
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be multiplied with a factor of 2 - 32, and divided by a factor of
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1 - 32. This makes it possible to generate almost any desired
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processor frequency. When using the Xilinx CLKDLL generator,
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the resulting frequency scale factor (mul/div) must be one of
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1/2, 1 or 2.
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WARNING: The resulting clock must be within the limits specified
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by the target FPGA family.
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System clock multiplier
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CONFIG_CLKDLL_1_2
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The Xilinx CLKDLL can scale the input clock with a factor of 0.5, 1.0,
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or 2.0. Useful when the target board has an oscillator with a too high
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(or low) frequency for your design. The divided clock will be used as the
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main clock for the whole processor (except PCI and ethernet clocks).
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System clock multiplier
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CONFIG_DCM_2_3
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The Xilinx DCM and Altera ALTDLL can scale the input clock with a large
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range of factors. Useful when the target board has an oscillator with a
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too high (or low) frequency for your design. The divided clock will
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be used as the main clock for the whole processor (except PCI and
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ethernet clocks). NOTE: the resulting frequency must be at least
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24 MHz or the DCM and ALTDLL might not work.
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Enable CLKDLL for PCI clock
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CONFIG_PCI_CLKDLL
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Say Y here to re-synchronize the PCI clock using a
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Virtex BUFGDLL macro. Will improve PCI clock-to-output
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delays on the expense of input-setup requirements.
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Use PCI clock system clock
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CONFIG_PCI_SYSCLK
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Say Y here to the PCI clock to generate the system clock.
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The PCI clock can be scaled using the DCM or CLKDLL to
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generate a suitable processor clock.
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External SDRAM clock feedback
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CONFIG_CLK_NOFB
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Say Y here to disable the external clock feedback to synchronize the
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SDRAM clock. This option is necessary if your board or design does not
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have an external clock feedback that is connected to the pllref input
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of the clock generator.
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