AM5728 using PCIe ljcb_clk pins as reference clock output

Hi,

I will ask the software team to look at this.

Hi. Ralf,
I am now going throgh problem of the pcie clockout, I used the SDK is am57xx-evm-sdk-src-02.00.01.07.
I setting the register CTRL_CORE_SMA_SW_6 => PCIE_TX_RX_CONTROL. But it's still can't work. and no signal output to ljcb_clk pins. Can you give me some important advice for this?



I will be very grateful to you.
Best Regards
Qing

Hi Qing,

I included the following lines in U-Boot and this seems to work for me:

/* Enable PCIe clock output 'ljcb_clk' => CTRL_CORE_SMA_SW_6.PCIE_TX_RX_CONTROL = 1 */
volatile unsigned int *CTRL_CORE_SMA_SW_6 = (volatile unsigned int *)0x4A003C14;
*CTRL_CORE_SMA_SW_6 = ((*CTRL_CORE_SMA_SW_6) & ~0x30000) | 0x10000;

Ralf

Hi, Ralf:
Thanks for your reply, but I also add same action into pcie-phy driver, but it's still no signal output.
and can you tell me your Ti SDK version?

Thank you very much!
Best Regards
Qing

I'm using PROCESSOR-SDK-LINUX-AM57X 03.00.00.04

Thank you very much!

Hi Ralf,

I also want to get PCIe Ref Clock output from Am5728 with Linux SDK V.03.02.

Can I get the PCIe ref clk output by changing the u-boot only as per your suggestion?

Thanks & Regards

Srikanta

Hi Srikanta,

the changes I made in U-Boot are working for me. But it seems that the clock output only gets active after some initialization in the Linux kernel.

Ralf

Hi Ralf,

Thanks a lot for your response.
For your case it was working by changing the u-boot only.
But for my case, why should I change Linux Kernel?
Could you please give some explanation regarding this?

Would you please tell me the u-boot file name where you have made changes?
Even if we need to change in Linux kernel, can you specify what needs to be modified and in which file(s) ?

Thanks & Regards
Srikanta

Hi Srikanta,

I think you missunderstood my statements.

A modification of the kernel should not be necessary.
I just tried to explain that the clock output doesn't become active immediately after executing the added code within U-Boot. It requires additional steps done by the Kernel, I guess something during initialization of the PCIe controller.

I have implemented the modification in custom U-Boot board code.
But I think it should be possible to put these lines into board_late_init() in board/ti/am57xx/board.c.

Please note that the delayed activation of the clock signal may violate reset requirements for connected PCIe devices. It's possible to let the kernel control the PCIe reset signal using a GPIO pin during initialization. But there is also a timing problem in the driver, see

Ralf

Hi Ralf,

I am very grateful to your explanation.

If it is known to you then please let me know the modifications in Ti SDK Kernel for PCIe clk output.

I am eagerly waiting for your reply.

Best Regards
Srikanta

I think you still don't understand me completely :-)
The Kernel is already doing the required steps for activating the clock signal, I'm just not sure what exactly they are.
But I think it's important to understand that the clock gets active relatively late in the boot process, because PCIe devices may require a valid clock signal when their reset signal is released.

Ralf