XIO2001: PERR doesn't get driven LOW with parity error...?

Darren (FAE)

Part Number: XIO2001

EDIT: Ignore this and go to the next post I wrote below. I understood the problem incorrectly here.

I have a customer working on a prototype board using the XIO2001 - and they are in the process of debugging.

Most features of the device seem to operate without any issues.

However, when they confirmed the behavior when try and instigate the parity alarm, the XIO2001 register shows parity error, but the PERR pin does not get driven LOW. It stays in Hi-Z.

What is the correct setup to get PERR to be driven LOW during such an error?

These are the register settings as seen from the CPU (PCIe) side.

70800000 : 104C 8240 0007 0010 0000 0604 0000 0001 .L.@............

70800010 : 0000 0000 0000 0000 0000 0000 0101 02A0 ................

70800020 : 0000 0000 0001 0001 0000 0000 0000 0000 ................

70800030 : 0000 0000 0040 0000 0000 0000 00FF 0001 .....@..........

70800040 : 480D 0000 0000 0000 5001 0603 0008 0040 H.......P......@

70800050 : 7005 0088 0000 0000 0000 0000 0000 0000 p...............

70800060 : 0000 0000 0000 0000 0000 0000 0000 0000 ................

70800070 : 0010 0072 8002 0000 2000 0010 4C11 0006 ...r.... ...L...

70800080 : 0000 1011 0000 0000 0000 0000 0000 0000 ................

70800090 : 0000 0000 0000 0000 0000 0000 0000 0000 ................

708000A0 : 0000 0000 0000 0000 0000 0000 0000 0000 ................

708000B0 : 0000 0900 0000 001F 0000 0000 0000 0000 ................

708000C0 : 0001 0208 0108 0012 2000 3214 0000 0000 ........ .2.....

708000D0 : 0000 0000 025F 8600 0000 0000 0040 0000 ....._.......@..

708000E0 : 0000 0000 0000 0000 0443 0008 007F 01C0 .........C......

708000F0 : 0000 0000 0000 0000 0000 0000 0000 0000 ................

70800100 : 0001 0001 0000 0000 0000 0000 2031 0006 ............ 1..

70800110 : 0000 0000 2000 0000 00A0 0000 0000 0000 .... ...........

70800120 : 0000 0000 0000 0000 0000 0000 0000 0000 ................

70800130 : 17A8 0000 1340 0000 0000 0000 0000 0000 .....@..........

70800140 : 0000 0000 0000 0000 0000 0000 0000 0000 ................

This is the method they are taking:

- The PCI bus cycle's data phase is set so that data with PAR=H can be written in the LSI (PCI side of the XIO2001)
- The CPU leads with long (32bit) data so that the address phase of the PCI bus cycle is PAR = L
- With the CPU leading, a switch connects the PAR pin (connected to XIO2001 and LSI) to 0V via 12Ω resistor - forcing a parity error
- Register 1E becomes 83A0, but the PERR signal stays Hi-Z

To confirm
- They write the LSI with data so PAR = L, then they do the same setup as above with the switch. 1E register area becomes 02A0, and PERR stays Hi-Z. This is expected behavior.

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 317480 points

A PCI device drives PERR low after it has detected a parity error while listening on the AD bus.

If I understand the description correctly, the CPU (one the PCIe side) does a downstream write to the PCI device, so the XIO2001 is not listening. When doing a write to the LSI, the LSI is responsible for signaling PERR.

0 Darren (FAE) over 4 years ago in reply to Clemens Ladisch

TI__Expert 5483 points

Hi Clemens,

I miss-interpreted the question from the customer.

They have a setup like in the below image. This is what really happens:
- During the PCI bus cycle, the CPU writes some data to the LSI so that during the data phase, PAR = H

Once the above has been done and there is data saved at that address of the LSI, we move on to reading that data.↓
- Then the CPU initiates a long (32-bit) read of an address that will have PAR = L during the address phase of the PCI bus cycle
- While the CPU is performing the data read, the SW (below diagram) is connected, to force a parity error during the data phase.
- When they do this, they see the XIO2001 displaying a parity error bit (83A0 in the 1E address of the Secondary Status Register), but the PERR is not driven LOW as expected.
- For reference, they do the same test but with the CPU writing some data to the LSI so that during the data phase, PAR = L. In this case, they see the value at register address 1E stay 02A0 - and the PERR pin remains in Hi-Z

They expected when the CPU is reading data from the LSI, that the XIO2001 should drive the PERR pin LOW as a parity error was detected. But they are not seeing this.

70800000 : 104C 8240 0007 0010 0000 0604 0000 0001 .L.@............

70800010 : 0000 0000 0000 0000 0000 0000 0101 02A0 ................