While EXTEST, PRELOAD, SAMPLE instructions are “JTAG instructions” that OpenOCD supports, the "D2000 Debug Operations User's Guide" only covers the instructions for debugging/development, not including the ones you mentioned that are more like used for manufacturing tests. I'd need to check whether we can disclose further info on the values used for EXTEST etc and will get back to you shortly.
Thanks for your help on this.
I would assume that a lot of your customers use boundary scan during PCB assembly as a way to detect solder shorts between IO pins, to ensure that balls were attached to the board properly, etc. So hopefully this is info that can be provided--or we'll be relying on AOI (automated optical inspection) and xray processes instead (especially when it comes to the BGA chips where the pins aren't visible).