Multiplexing JTAG and EZport Pins In CPLD

[kevinkirspel]

In my system I will have 2 processors.  An iMX6 host processor for the GUI and a Kinetis K10 for real-time processing.  The iMX6 will be able to program the K10 through the EZPORT interface.  I will also be using a Segger J-link with the K10.  On the K10, there are 3 JTAG pins that are multiplexed with EZPORT pins.  I was going to route these pins through a CPLD which would have logic to switch these signals between the iMX6 and the Segger J-Link.  By default the pins will be switched to the J-link.  If the iMX6 wants to program the K10, it will switch the pins using one of its DIO pins.  Does anyone see a problem with this?  I have attached a diagram to illustrate the idea.

[Dekiru · Accepted solution]

Hi Kevin,

I think that there is not any problem with multiplexing pins using this method, but there are some points you should consider:

- Jlink supports both JTAG and SWD (SWD using 2 pins only). If you use SWD instead of JTAG, there is only one shared pin.

- Unless you use CPLD for something else already, it is not cost effective to use CPLD just for multiplex 1-3 pins.

- EzPort requires reset circle so do not forget to design it in a way that you can control reset pin of K10

- I am not sure if you had a look at Vybrid platform or not but Vybrid can help to reduce cost and size of the system where both realtime app and rich user interface are needed.

Regards

[kevinkirspel]

I already have a CPLD for other things so it cost me nothing to add this functionality.  I will look into the Vybrid platform.

[Kan_Li]

Actually, in my understanding , the function of the CPLD can be replaced  by some jumpers, since JTAG and EZport can not be used in the same time.