XCore Exchange

I just had a awesome idea... how about using a MULTIPLEXER in reverse?

74ls157 for example... (Would this work?)

or 74VHC4066
or 74CBTLV3126

Or you could decide not to route a link to the XSYS at all,
not muck up your clean simple design with a muxing thing
that I promise you will be complicated to use. Do you really
want to lose a 4b/8b port anyway, in any configuration?

yeah, i guess ill leave this design as is and a future design add that.

On the other hand, can't you use link C for xscope? Losing
the four port 32A signals wouldn't be nearly as bad for most
applications (you still have the much more useful sixteen 1b
ports and an 8b or two 4b). Or does it have to be link B?
I've never used xscope, sorry.

I never used it as well... Im going to do this design as is and plan another one slightly larger and smaller...

If this board works then i will understand some of the process and can make 2 new pcbs...

1) BASE/DEV board which will house a full xSYS connector with all links and be used for debugging.
2) TRAVEL board which would be a basic xSYS connector JTAG only for programming and all IO usable.

This will allow one to use the BASE for testing and TRAVEL in final designs since its more compact...

Hows that sound?

The use of IC2 & IC1 as drawn does not make sense to me. You are attempting to hold reset down low till the power rails (3.3 volt & 1 volt are stable). At the very least, you do not need to cascade 2 of the same devices with a 2.9 volt threshold as drawn. The recommendation I think you want is when the 3.3 volt rail is stable, enable the Semtech SC189C (ie. EN pin will be high through the pull-up to enable the 1.0 volt rail switcher). However, even that is not required since the SC189C (we actually use the SC183C but yours should be fine) operates from a min of 2.9 volts - that is, by design, SC189C should be ok as-is without the need for a voltage supervisor. However, you are not (yet) monitoring if the 1.0 volt is stable before releasing the reset of the XMOS device. Perhaps too much paranoia and may not be required but I would quickly review if you can find a quality LDO (with ample current) and a power good output for the 1.0 volt rail. We had located the Richtek RT9041A which should be suitable but no stock to be found. As noted, it is quite possible that all you need is a single power rail supervisor but technically, the power sequence should be +3.3 volt -> check if stable -> enable 1.0 volt -> check if stable -> now release reset.

I thought that myself as well but saw it somewhere else and forgot where... but thats how it was. Im sure i can use just one on the 3.3v line..

segher wrote:On the other hand, can't you use link C for xscope? Losing
the four port 32A signals wouldn't be nearly as bad for most
applications (you still have the much more useful sixteen 1b
ports and an 8b or two 4b). Or does it have to be link B?
I've never used xscope, sorry.

AFAIK you can use any link as long as it is appropriately configured in the XN file.

One other possibility is to route the 4 link tracks to one row of a 2x4 header (adjacent to JP3) and connect the other row to XSYS, that way it can be jumpered for xscope or you can just tap the headers when you need the extra IO pins. slightly ugly but it should work perfectly.

regards
Al

mon2 wrote:The use of IC2 & IC1 as drawn does not make sense to me. You are attempting to hold reset down low till the power rails (3.3 volt & 1 volt are stable). At the very least, you do not need to cascade 2 of the same devices with a 2.9 volt threshold as drawn. The recommendation I think you want is when the 3.3 volt rail is stable, enable the Semtech SC189C (ie. EN pin will be high through the pull-up to enable the 1.0 volt rail switcher). However, even that is not required since the SC189C (we actually use the SC183C but yours should be fine) operates from a min of 2.9 volts - that is, by design, SC189C should be ok as-is without the need for a voltage supervisor. However, you are not (yet) monitoring if the 1.0 volt is stable before releasing the reset of the XMOS device. Perhaps too much paranoia and may not be required but I would quickly review if you can find a quality LDO (with ample current) and a power good output for the 1.0 volt rail. We had located the Richtek RT9041A which should be suitable but no stock to be found. As noted, it is quite possible that all you need is a single power rail supervisor but technically, the power sequence should be +3.3 volt -> check if stable -> enable 1.0 volt -> check if stable -> now release reset.

To quote from Xmos about L series power sequencing:

The VDDIO supply must be within specification (3.0V - 3.6V) before the VDD (core) supply reaches 0.4V. The VDD (core) supply should ramp monotonically (constantly rising) from 0V to its final value (0.95V - 1.05V) within 10ms to ensure correct start-up. The VDD (core) supply should be capable of supplying at least 300mA for an L6/8-64 and 600mA for an L8/10/12/16-128 device assuming they may be operating at full capacity.

The circuit can be optimised with the right regulator with a power good output, it can also be hacked and the early XK1 had a power supply sequence that didn't follow Xmos's own rules, however I believe they fixed it later.

regards
Al