LS1012A RGMII clocking

[luka_pirnat]

Hi there!

We're designing a LS1012A board and we'll be using an RGMII PHY (VSC8531) to connect to the outside world via Ethernet. Now, due to conflict between the CPU Reference Manual and the Design Checklist AN5192 I'd like to make sure it's okay to use two separate clock oscillators for CPU and PHY. Because the ref man only depicts two use cases - the first being using two crystals (CPU and PHY) and the second using a common clock oscillator for both. While in AN5192 the first case is the same and the second shows using a clock osc for CPU and crystal for PHY.

So, is it okay to use two separate clock oscillators/generators for CPU (25MHz) and RGMII PHY (125MHz)? I know the ARDB board does that, but there's also a 0-ohm option left to allow connecting the CPU's ref. clock to the PHY...
The reason for asking this is also a similar problem that existed with SGMII before CPU revision 2.

Thanks,
Luka

[r8070z · Accepted solution]

Have a great day,

It is Ok to use two separate clock oscillators/generators for CPU (25MHz) and RGMII PHY (125MHz).

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