So we have a SER DS90UB947 to a DES DS90UB926. The '926 is on a remote display without smarts. We want to test the link as part of our BIST sequence at boot.
The kickers are: the BIST can only be started by the DES, there are no smarts (MPU) at the DES end.
We have considered a number of options. The leading candidates are
1. using an I2C "bus extender" (basically an I2C-driven register) on the DES side to assert BISTEN
1a. do the same, but with the SPI link
2. configuring a GPIO on the DES (via actions on the SER side) that we can set the GPIO on the DES to loop back to BISTEN
3. Configuring the INTB on the DES (via actions on the SER side) that we can set the INTB on the DES to loop back to BISTEN
Whatever way we get BIST started, the BIST should not prevent us from stopping the BIST.
To determine the status of the BIST, we should be able to look at the error count register. On the DES side, we could latch any roisters on the PASS output and use GPIO (or the bus extender register) to read the latch (the only reason for the latch is apparently PASS will pulse low between BIST runs if you continue another BIST run...)
We will be cutting hardware soon, so we would like to get this nailed while at the schematic stage. Unfortunately, I don't have hardware to play with this.
