AM2732: Question about reference clock in RMII mode of CPSW (ethernet interface)

Chris Meng

Part Number: AM2732

Hi,

My customer would like to use RMII to external phy. What's the pin of AM2732 for MSS_M1II10_CLK signal in below figure which is copied from AM2732 TRM?

My customer would like to know if the reference clock can be output by AM2732 or must be input by external phy to AM2732. Would you pls help?

Thanks,

Chris

over 3 years ago

0 Prasad Jondhale over 3 years ago

TI__Mastermind 27743 points

Hi Chris,

on (1) - Quickly looking at TRM, the clk signal shown in diagram is available on MCU_CLKOUT pin of SOC.

I will also ask our HW apps expert to review this.

on (2), the RMII 50MHz needs to be input both to PHY or CPSW MAC. Some PHY chips has capability to generate this internally which can be used for it's own input as well to feed to AM273x.

In AM273x, as shown in diagram you attached, we have way to generate 50MHz clock on SOC pin which can be used to feed to PHY as well MAC.

Regards,

Prasad

0 Chris Meng over 3 years ago in reply to Prasad Jondhale

TI__Mastermind 39306 points

Prasad,

Thanks for your reply!

So any clock out pin which can output 50Mhz can be the MSS_MII10_CLK, right?

Waiting for your confirm from HW apps on this.

Best Regards,

Chris

0 Shivasharan Nagalikar over 3 years ago in reply to Chris Meng

TI__Expert 8670 points

Hi Chris, MII100_CLK is routed to MSS_RMII_REFCLK (PADBX) pad . So you could use that pin as 50MHz. Its a bi-directional pin (we will update the DS & TRM)

Best Regards, Shiv

0 Chris Meng over 3 years ago in reply to Shivasharan Nagalikar

TI__Mastermind 39306 points

Shiv,

Thanks for your reply.

How to configure MII100_CLK to route MSS_RMII_REFCLK (PADBX) for RMII mode?

Is there any register need to set for MSS_RMII_REFCLK (PADBX) to be input or output in RMII mode?

Thanks,

Chris

0 Shivasharan Nagalikar over 3 years ago in reply to Chris Meng

TI__Expert 8670 points

Hi Chris,

You can use PADBX_cfg_reg Register and select mux mode 2 for RMII.

Best Regards, Shiv

0 Chris Meng over 3 years ago in reply to Shivasharan Nagalikar

TI__Mastermind 39306 points

Shiv,

PADBX_cfg_reg is pinmux function config. How to configure it to work as input or output?

Thanks,

Chris

0 Chris Meng over 3 years ago in reply to Chris Meng

TI__Mastermind 39306 points

Shiv,

Would you pls help again?

I think we need to configure the PADBX pin direction then the CPSW will know the 50Mhz is input to PADBX or output from PADBX.

Thanks,

Chris

+1 Daniel Bermudez over 3 years ago in reply to Chris Meng

TI__Expert 8390 points

Hi Chris,

Chris Meng said:
PADBX_cfg_reg is pinmux function config. How to configure it to work as input or output?

Datasheet specifies the following:

Even though this is a bi-directional pin, function 2 (MSS_RMII_REFCLK) is reserved to be used as in input and this cannot be changed without changing the pin function as well.

Chris Meng said:
How to configure MII100_CLK to route MSS_RMII_REFCLK (PADBX) for RMII mode?

If this is the goal then it is already being done by default:

TRM integration specifies the following:

TRM description specifies that:

So MII100_CLK already routes to PADBX via RMII_REF_CLK

Additionally, RMII_REF_CLK can be selected from two sources controlled by register MSS_CTRL:CPSW_CONTROL:RMII_REF_CLK_OE_N:

0h: clock will be from mss_rcm through internal loopback
1h: clock will be from PAD loopback

As the reset value of this register is 0h, the MSS_RCM source MSS_MII100_CLK is already being selected as a source for RMII_MHZ_50_CLK

Best,

Daniel

Link to TRM: https://www.ti.com/lit/ug/spruiu0a/spruiu0a.pdf?ts=1666993868824&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FAM2732%253FkeyMatch%253DAM273X

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AM2732: Question about reference clock in RMII mode of CPSW (ethernet interface)