SPI 4: Observation - Alternate Wiring


Just wondering if there any more details on why the chip clip → Tigard → Bitmagic setup doesn’t work and a firmware update etc was ever able to fix it (as it seems like useful functionality)?

I tried it using the above setup after completing the exercise to note the difference and largely didn’t get any data on the COPI/CIPO pins, only really seeing expected data on CS & CLK, is this what you experienced originally?

Just looking for understanding, thanks!

While this was a planned functionality of Tigard, it turned out to not work consistently due to an issue with the level shifters.

When using the logic analyzer wiring, consider there are 3 players involved with each wire: 1) the logic analyzer 2) the target and 3) the Tigard’s FT2232H via level shifters

The logic analyzer passthrough basically wants to connect #1 to #2, while #3 should just stay quiet. For the FT2232H inputs this is easy, for the outputs, we need to silence them somehow. The level shifter has an ‘enable’ signal we should be able to use to ‘disable’ these outputs - except that we’ve encountered is that while the level shifter is powered off, some current leaks through the input and enables the level shifter. This is not the behavior expected based on the datasheet, and not something firmware-fixable.
I hope to test level shifters from other manufacturers to see if there’s an easy fix, but that’s a hardware change and there won’t be another revision of Tigard at least until FT2232H chips are readily available again (2023 last i checked…)

Depending on the target, wiring, and voltage, i would hope to see at least CIPO data. If the wiring is robust, the level shifters might prevent the target from actually speaking on any of the SPI wires. If the wiring is flakier, then the target might be able to get some SPI traffic, but the flakey wiring would at best prevent you from seeing it, and at worst, cause enough signal integrity degradation that the target could no longer communicate with the SPI flash chip.

So - while overall it was an optimistic idea, in practice, it’s not that great unfortunately. :frowning:

Really useful and interesting, thanks!

Useful to just have an idea of why as it all helps build the picture of how it all interacts.