Other Parts Discussed in Thread: DP83TC811
Hello Colleagues,
I'm trying to understand the timing budget of the RGMII link of the DP83TC811.
My layout can be considered perfect, all lines matched less than 1 cm. (Both RX and TX) At least this can be excluded from the equations.
The clock is 25MHz, data lines (RX and TX) are SDR and the control lines (RX_CTRL, TX_CTRL) are DDR as specified in the datasheet, and RGMII specification.
The clock period is 40 ns.
First I would like to figure out how to configure clock delay.
My current setup is:
PHY: TX Shift mode (internal delay) RX Shift mode (internal delay)
MAC:TX Aligned mode (internal delay) RX Aligned mode (internal delay)
I think this setup is correct, but when doing the measurements the RX shifting will be visible, and the TX shifting will happen in the PHY.
When the setup is:
PHY: TX Shift mode (internal delay) RX Aligned mode (no internal delay)
MAC:TX Aligned mode (no internal delay) RX Shift mode (internal delay)
I'll see the bus aligned, but I will never be sure, if my setup is correct, since I cannot measure the internal signals in PHY or MAC.
(Let's assume, that I don't know anything about the SW, at any point of time. I can be sure about what the oscilloscope is showing to me. )
Then it could be more convincing to set as follows:
PHY: TX Aligned mode (no internal delay) RX Shift mode (internal delay)
MAC:TX Shift mode (internal delay) RX Aligned mode (no internal delay)
I'll see the clock delayed, so I can be sure, that at least before the receiver blocks (PHY - TX, MAC - RX), the clocks are correctly delayed.
However at this low speed, I could add delay for both RX and TX on both MAC and PHY side , it wouldn't cause any problem. (assume 2 ns in MAC, and 2ns in PHY )
PHY: TX Shift mode (internal delay) RX Shift mode (internal delay)
MAC:TX Shift mode (internal delay) RX Shift mode (internal delay)
Then I'll see both RX and TX clock delayed, but there will be even more inside MAC-RX and PHY-TX.
What do you think?
If you could do any of the above mentioned setups, which one would you prefer and why?
Many thanks!
