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[T1040QDS] [eSPI] ESPI_SPCOM[DO] clarifications

Question asked by Rommel Custodio on Apr 24, 2014
Latest reply on May 20, 2014 by Serguei Podiatchev

Dear All, Freescale Engineers,


Now studying the eSPI block but I can't find any AppNote about eSPI and ESPI_SPCOM[DO].


The connected serial NOR flashes seems to support Dual mode.

So I'm modifying FSL u-boot 2013.10 (the usual suspect) and working with CS#0 (Micron part).

I'll be referring to T1040RM_RevC.pdf in the text below.



Kindly correct any mis-understandings:

1) ESPI_SPCOM[DO] affects DQ[1:0] for both INPUT and OUTPUT OR only during OUTPUT only?

In my mind, the statement in 20.5 seem to imply that ESPI_SPCOM[DO] affects DQ[1:0] only during OUTPUT.



The answer to question 1) affects my other understanding.

If ESPI_SPCOM[DO] is only for OUTPUT that means I do not need to program the Serial NOR device to Dual mode.

For example sending the DUAL OUTPUT FAST READ , in Dual mode, the Micron expects Address INPUT to use also DQ[1:0].

Though in Extended mode, Address INPUT is thru DQ0 but Data OUTPUT can use DQ[1:0].



2.a) ESPI_SPCOM[DO] can be enabled on a transaction basis.

For example, use READ ID (with ESPI_SPCOM[DO] = 0), then start a FAST READ (with ESPI_SPCOM[DO] = 1).




2.b) ESPI_SPCOM[DO] is persistent until the next power cycle.

From statement in 20.3.4, my understanding is ESPI_SPCOM[DO] must be set for very first command send to Serial NOR device.

Device detection should not use READ ID. This means that Serial NOR device (Micron) must be also in Dual mode prior.

Here lies a chicken-and-egg problem since I want to program the Dual mode in the Enhanced Volatile Configuration Register only

(i.e. the Micron will always reset to Extended mode after a power reset).



3) It seems drivers/spi/fsl_espi.c:spi_xfer() does not check ESPI_SPIE[DON].

Though it seems it doesn't really matter since we can only perform one transaction at a time in u-boot.



4) What other settings affect ESPI_SPCOM[DO]?

Do you have equations for the correct calculation of ESPI_SPMODE[HO_ADJ]?



Your expertise will be highly appreciated.


All the best,