imx6 RGMII RX interface voltage too low

[andy_cc_huang]

Hi ,

   We have a imx6solo custom board and use RGMII + marvell 3.3v phy .

Our circuit is     RGMII RX pins + level shifter + marvell phy

                          RGMII TX pins + level shifter + marvell phy

In this situation ,  imx6 tx packets are ok,  but RX pins voltage will drop to 2.0v.

And then we remove level shifter ,   marvell tx come out correct 3.3v  after measuring.

In the end , we wired marvell tx + imx6 rx RGMII directly ,  but the voltage is still drop to 2.0v.

We try our all  RX DSE and PUS combination but no help.

Do you have any idea to debug this ?

Here is our pin defination.

pinctrl_enet: enetgrp {
fsl,pins = <
MX6QDL_PAD_ENET_MDIO__ENET_MDIO 0x1b0b0
MX6QDL_PAD_KEY_COL2__ENET_MDC 0x1b0b0

MX6QDL_PAD_RGMII_TXC__RGMII_TXC 0x1b0b0
MX6QDL_PAD_RGMII_TD0__RGMII_TD0 0x1b0b0
MX6QDL_PAD_RGMII_TD1__RGMII_TD1 0x1b0b0
MX6QDL_PAD_RGMII_TD2__RGMII_TD2 0x1b0b0
MX6QDL_PAD_RGMII_TD3__RGMII_TD3 0x1b0b0
MX6QDL_PAD_RGMII_TX_CTL__RGMII_TX_CTL 0x1b0b0

MX6QDL_PAD_ENET_REF_CLK__ENET_TX_CLK 0x1b0b0

MX6QDL_PAD_RGMII_RXC__RGMII_RXC 0x1b0b0
MX6QDL_PAD_RGMII_RD0__RGMII_RD0 0x1b0b0
MX6QDL_PAD_RGMII_RD1__RGMII_RD1 0x1b0b0
MX6QDL_PAD_RGMII_RD2__RGMII_RD2 0x1b0b0
MX6QDL_PAD_RGMII_RD3__RGMII_RD3 0x1b0b0
MX6QDL_PAD_RGMII_RX_CTL__RGMII_RX_CTL 0x1b0b0

MX6QDL_PAD_GPIO_16__ENET_REF_CLK 0x4001b0a8

>;
};

Best,

Andy

[igorpadykov · Accepted solution]

Hi Andy

this may be hardware related, please check how powered RGMII

pins with oscilloscope using i.MX6SDL Datasheet Table 8. Operating ranges,

Table 96. 21 x 21 mm Functional Contact Assignments

http://cache.freescale.com/files/32bit/doc/data_sheet/IMX6SDLCEC.pdf

Just for test one can attach jtag (or printf iomux register) to verify that register

MX6QDL_PAD_RGMII_RD is configured as input.  Disconnect input from marvell phy

and configure it as pull-up with PUS, there should be high level with value of RGMII power supply.

Best regards
igor
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[andy_cc_huang]

Hi  Igor,

   Thanks for your reply. We found our marvell phy can not provide enough current for the i.mx6.

So we force the speed to 100M and I can ping successfully.

Best,

Andy