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CPU Clock and FPGA clock interaction
Added by Steven Hill almost 11 years ago
For various reasons I would prefer an FPGA clock of 96 MHz. Am I right in assuming that if I modify the kernel to get a CPU clock of 288 MHz I will get what I want? If so, which file in the kernel do I need to modify to get my desired CPU frequency?
Replies (2)
RE: CPU Clock and FPGA clock interaction - Added by Michael Williamson almost 11 years ago
Hi Steven,
If you need a specific frequency for your FPGA, I would recommend adding an external Crystal or Oscillator to your design and bringing it into the FPGA via one of the available GCLK pins. From there you can PLL the frequency to whatever you need.
You may be able to use a PLL or DCM and modify the input EMIFA 100 MHz clock (at 300 MHz CPU) to get what you want as well.
If you are running linux (or any of your other peripherals) and you define a new operating point (currently supported are 96, 200, 300, 372, 408, and 456 MHz) you may be in for more headaches that it is worth as you will be impacting most of the clock tree within the kernel and device driver structures. The OPPs are defined in arch/arm/mach-davinci/da850.c. It's not for the faint of heart.
Is there something specific driving your 96 MHz requirement? How accurate?
-Mike
RE: CPU Clock and FPGA clock interaction - Added by Steven Hill almost 11 years ago
Based on what you have told me about Linux operating points, I won't be fooling with the CPU frequency. I will find a workaround to get the clocks I need on the FPGA...
