FCS-Link2

Fibre Channel to S-LINK Interface
Reset procedure

INTRODUCTION

The Fibre Channel to S-LINK Interface should follow the reset procedure as described in the S-LINK specification. This is a local reset of one side of the link with a kind of handshake between the URESET# and LDOWN# signals. The S-LINK specification describes only the reset of one side of the system (LSC or LDC) and not the reset of the full system (LSC and LDC). That, together with some undefined features of the ENDEC chip used on the board, makes that it is not always clear how one can make a system reset that works always.

This document describes measurements of the behaviour of the reset of the FCS-LINKs and describes a fail-proof method of resetting the links.

Note that this behaviour of the most used version (EPROMs marked S4c4 and Db29). In fact a new version is available which complies completely to the S-LINK specification. You may ask Zoltan Meggyesi about upgrading.

MEASUREMENTS

The following measurements have been made with a setup with FCS-LINK2 cards mounted on SLITEST cards with a SLIDAS and SLIDAD (see SLITEST documentation).

Table 1: Reset procedure after power cycle of LDC

LSC LDC

Power off LDC => down (no power)

Power on LDC => down up

Reset LSC => up up

This is always OK

Table 2: Reset procedure after power cycle of LSC (start with reset LDC)

LSC LDC

Power off LSC => (no power) down

Power on LSC => down down

Reset LSC => down (still!) down

Reset LDC => up up (mostly) / down (sometimes)

Reset LDC => up up

(resetting the LSC several times doesn't make a difference)
The bad thing here is that resetting the LDC can make that the LDC does not always go up (and instead the LSC goes up)

Table 3: Reset procedure after power cycle of LSC (start with reset LSC)

LSC LDC

Power off LSC => (no power) down

Power on LSC => down down

Reset LDC => up up

or sometimes the following happens:

LSC LDC

Power off LSC => (no power) down

Power on LSC => down down

Reset LDC => down up

Reset LSC
(not needed) => down up

Reset LDC => up up

So it seems that sometimes you need to reset the LDC twice before the whole link comes out of reset. The bad thing is that you need to reset the LDC twice, while it's LDOWN# says the link is already up on that side.

		LSC	LDC
Power off LDC	=>	down	(no power)
Power on LDC	=>	down	up
Reset LSC	=>	up	up

		LSC	LDC
Power off LSC	=>	(no power)	down
Power on LSC	=>	down	down
Reset LSC	=>	down (still!)	down
Reset LDC	=>	up	up (mostly) / down (sometimes)
Reset LDC	=>	up	up

		LSC	LDC
Power off LSC	=>	(no power)	down
Power on LSC	=>	down	down
Reset LDC	=>	up	up

		LSC	LDC
Power off LSC	=>	(no power)	down
Power on LSC	=>	down	down
Reset LDC	=>	down	up
Reset LSC (not needed)	=>	down	up
Reset LDC	=>	up	up

Once a link is up on both sides, you may give a reset on one side without impacting the other side or the link. So it doesn't matter if you give a reset too many on one side. However, during that reset the link will not be functional (also the return lines don't work and give out all 0's).

CONCLUSION

The best way of resetting the FCS-LINK is that when you see LDOWN# active on a side, is to reset that side twice. This procedure should always work (any order of power up, or cable insertion).
Once a link is up on both sides, you may give a reset on one side without impacting the other side. However, during that reset the link will not be functional (also the return lines don't work).
A new version PROM is available, which makes the reset behaviour fully compliant to the S-LINK specification. You may ask Zoltan Meggyesi about upgrading.

CONTACTS

Hardware: Zoltán Meggyesi
Measurements: Erik van der Bij