XIO2001: the difference between GRST and PERST

Noriyuki Takahashi

Genius 11570 points

Part Number: XIO2001

Tool/software:

Hi team

Could you tell the difference between GRST and PERST?

Could you also tell when they should use GRST and PERST?

Regards,

Noriyuki Takahashi

5 months ago

0 Brian Zhou 5 months ago

TI__Guru**** 154260 points

Hi Noriyuki :

GRST is general reset for all XIO2001.

PERST is PCIe reset for XIO2001 PICe interface.

Best

brian

0 Noriyuki Takahashi 5 months ago in reply to Brian Zhou

TI__Genius 11570 points

Hi Brian,

According to table 8-1, /PERST is used to reset all control register bis that are not indicated by d by the ☆ symbol. Is this right?

However, I can't see any registers with the ☆ symbol in the datasheet. How should I understand registers for /PERST?

Regards,

Noriyuki Takahashi

+1 Brian Zhou 5 months ago in reply to Noriyuki Takahashi

TI__Guru**** 154260 points

Hi Noriyuki :

It seems datasheet is not consistent, bit with (2) are sticky bits.

Best

Brian

0 Noriyuki Takahashi 4 months ago in reply to Brian Zhou

TI__Genius 11570 points

Hi Brian,

Thanks.

They are still not sure when /PERST needs to be used. Could you tell when they should use /PERST?

Regards,

Noriyuki Takahashi

0 Brian Zhou 4 months ago in reply to Noriyuki Takahashi

TI__Guru**** 154260 points

Hi Noriyuki :

an upstream PCI Express device to generate a PCI Express reset and to signal a system power good condition.

When PERST is asserted low, the XIO2001 generates an internal PCI Express reset as defined in the PCI Express specification.

When PERST transitions from low to high, a system power good condition is assumed by the XIO2001.

Note:

The system must assert PERST before power is removed, before REFCLK is removed or before REFCLK becomes unstable.

Best

Brian

0 Noriyuki Takahashi 4 months ago in reply to Brian Zhou

TI__Genius 11570 points

Hi Brian,

Sorry, I am still not sure when /PERST is used in terms of system perspective.

Based on the datasheet, it seems that /PERST needs to be used during power-up/down sequnencing. Is this right?

Are there any other case else when /PERST should be used?

Could you also confirm below?

When PERST is asserted low, does the device asserts PCI bus reset ( PRST)?

They understand that GRST is asserted low, the bridge asserts PCI bus reset ( PRST).

Regards,

Noriyuki Takahashi

0 Brian Zhou 4 months ago in reply to Noriyuki Takahashi

TI__Guru**** 154260 points

Noriyuki Takahashi said:
it seems that /PERST needs to be used during power-up/down sequnencing. Is this right?

correct. PERST# signal is an open drain, active low output from the root port. It is released when all power rails and the REFCLK signal have stabilized.

Noriyuki Takahashi said:
Are there any other case else when /PERST should be used?

PERST signal is also used in the PCIe L2/L3 low power mode exit sequence..

Noriyuki Takahashi said:
When PERST is asserted low, does the device asserts PCI bus reset ( PRST)?

They understand that GRST is asserted low, the bridge asserts PCI bus reset ( PRST).

both are correct.

Best

brian

0 Noriyuki Takahashi 4 months ago in reply to Brian Zhou

TI__Genius 11570 points

Hi Brian,

When PERST is asserted low, does the device asserts PCI bus reset ( PRST)?

Regards,

Noriyuki Takahashi

+1 Brian Zhou 4 months ago in reply to Noriyuki Takahashi

TI__Guru**** 154260 points

When PERST is asserted low, XIO2001 asserts the internal PCI bus reset. but not on PRST terminal.

Best

brian

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XIO2001: the difference between GRST and PERST