LS1027A Cannot reboot

[mikelooijmans]

We have a custom board with LS1027A CPU on it.

When I attempt to reboot the board from Linux, the system doesn't actually reboot, all it does is write this on the serial terminal and then hangs:

reboot: Restarting system
Unable to restart system

Out board looks so much like the LS1028ARDB board, it will actually boot the same image, and on that board, the reset works as expected.

Same issue with u-boot, if I type "reset", nothing happens and the prompt just returns.

What did we miss?

[June_Lu]

You could refer to LS1028A Reference Manual and AN12028_QorIQ LS1028A Design Checklist for the RESET_REQ_B detail information.

Once asserted, RESET_REQ_B does not negate until PORESET_B is asserted.

But another thing need to confirm, when assert PORESET_B, please follow LS1028A/LS1018A Data Sheet, page 75, Table 13. RESET initialization timing specifications.

So when connect them directly, please confirm the different conditions.

Thanks

[mikelooijmans]

We did some more digging with the scope.

On the LS1028ARDB, the RESET_nREQ pin goes to an FPGA. On our board it only has a o pull-up as the datasheet suggested.

When I attempt to reboot, the RESET_nREQ asserts low and nothing else happens.

On the LS1028ARDB, the RESET_nREQ asserts low and then the FPGA pulls the nPORESET low, which causes the reboot.

So we attempted the obvious and tied these two pins together. This caused the board to no longer boot at all.

Next thing we tried was route the RESET_nREQ to an input of the power-supply monitor chip that controls the nPORESET signal, so that when RESET_nREQ asserts, the monitor chip will assert the nPORESET signal for several milliseconds.

This appears to work in our testing.

Question to NXP engineers is now, is this how it's supposed to work?

Is the maybe some application note on this reset signal that explains how these signals are supposed to work? The datasheet is rather vague about it.

[June_Lu]

Would you kindly share the logs? Both Linux and U-Boot.

Thanks

[mikelooijmans]

What logs are you referring to?

u-boot doesn't output anything (when I type "reset").

Kernel only outputs those two lines.