SAMA5D33 GMAC RGMII mode TX Clock output problem

Discussion around products based on ARM Cortex-A5 core.

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SAMA5D33 GMAC RGMII mode TX Clock output problem

Thu Jan 02, 2014 5:08 am


We use SAMA5D33 GMAC with RGMII mode but encountered a problem about TX clock output.

We stopped bootloader count down, and inspected RGMII TX clock output (pin R5) immediately by the following register settings in bootloader:

mw 0xf0028004 0x00300403
mw 0xf002800c 0x1

We could see 125MHz clock output on pin R5 from the purchased SAMA5D33 CPU module.
But on our own design, we only saw the signal of pin R5 raised from low to high, no clock output.

We checked every power input of our SAMA5D33 to make sure it was supplied by correct 3.3V / 2.5V / 1.25V, and it was with correct 12MHz / 32.768KHz crystal input.
We thought our SAMA5D33 should have the same condition like purchased SAMA5D33 module, but it didn't work for RGMII mode.

We think it would be related PLL inside SAMA5D33 but we have no idea about how it works to check more deeper.

Could anyone give us some suggestions to check or some further registers to let RGMII work?


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