What does the error "SIF_LOADB already low" mean, and what should I do about it?

SIF_LOADB refers to the nSIF_LOAD line used for programming/debugging the EM2xx IC via the 10-pin InSight Port interface. As this line is active-low, it should typically be idling at a high logic level. If the programming utilities (em2xx_load or EM2UsbLoad) detect that the line is idling at a low level (not above the VDD_PADS threshold for high logic) before he programming mode is engaged, they will trigger an error to indicate that the line was in an unexpected state.

This kind of problem usually indicates a hardware issue. As a sanity check, try loading the same firmware via the same InSight Adapter (ISA) over the same programming cable assembly, but connected to a known-good piece of hardware (such as an Ember RCM from a development kit). If the issue persists there, try substituting the InSight Adapter and/or cable in case those have become faulty.

Assuming that the test against “golden unit” hardware works well with a given ISA/cable but still fails on a custom design, you should check that the design confirms to the latest revision of the reference design used for the basis of the design. The most recent version of the designs can be found at http://www.ember.com/products_documentation.html. You should also double-check the continuity and components around the SIF lines, including proper pull-up resistors and glitch filters. Note that the latest EM2xx reference designs (as of this writing) advise a 560-ohm (replacing 10k-ohm) pull-up resistor for nSIF_LOAD to improve noise immunity on the SIF bus.

You should also check that the nSIF_LOAD line has proper voltage going to it (or proper power on the chip in general), as a bad power/ground plane can cause logic inconsistencies or lack of signal on the I/O lines of the programming interface.