Interfacing Micro SD card and emc memory both

[Ankurd477]

I am designing a hardware in which i am using Compute module. i want to use memory card in my hardware to support some logging functionality in my hardware and i need the EMC memory at the same time.
How can these both be interfaced together?

[aBUGSworstnightmare]

Make use of the second uSD card interface. Consult the users manual for details

[Ankurd477]

Thanks for replying.
Actually while referring to manual, there is a little confusion that we can either use emmc or SD card.
Can you please guide specifically?

[aBUGSworstnightmare]

When using CM3 you CAN'T connect uSD to SD0-pins (refer to chapter 5 pin assignment of CM user's Manual), but you can use SD1 - second Interface (SD1) for connecting SD, SDIO or eMMC devices (chapter 9)

9.1.4 SD/SDIOInterface
The BCM283x supports two SD card interfaces, SD0 and SD1. The first (SD0) is a proprietary Broadcom controller that does not support SDIO and is the primary interface used to boot and talk to the eMMC or SDX x signals. The second interface (SD1) is standards compliant and can interface to SD, SDIO and eMMC devices; for example on a Raspberry Pi 3 it is used to talk to the on-board BCM43438 WiFi device in SDIO mode. Both interfaces can support speeds up to 50MHz single ended (SD High Speed Mode).

When using CM3L you can connect one uSD to SD0 and use SD1 a decribed above.

Users Manual is here https://www.raspberrypi.org/documentati ... CM_2p0.pdf

[Ankurd477]

Thank you so much, that solved my problem to much extent, but still one doubt is there
Since i have to boot my board using EMMC and use external memory card for logging purpose.
in attached images i have highlighted two things-
i.e. GPIO22-27 have both SD0 as well as SD1.
1) Could it be used as both? i.e. if i have to interface external memory card, we can connect it with these pins?
and in schematic they are referred as SDX, what is X in that?
2) And secondly there are also GPIO35 - GPIO43, that has also SD1, should i use these pins for interfacing external card? That is it's alternative function.
https://drive.google.com/open?id=1MzFs0 ... 7QRpdgH7tr
https://drive.google.com/open?id=1DJtzR ... ge6Esyr1XV

[aBUGSworstnightmare]

SD0 is talking to SDx signals. Connected to SDx is either your boot uSD (in case of CM3L) or your eMMC (CM3).

SDX is the Name of the Primary uSD/eMMC ínterface.
Table 9.1.1 gives you GPIO alternate functions (Alt0 - Alt5).

Honestly speaking, I've never thought about what happens when you try to configure GPIO22-27 to ALT0-function on i.e. a CM3.... I'm not even sure is this would be possible at all as SD0 (on GPIO22-27) is shown as 'reserved' function in the BCM2835 ARM Peripherals document(https://www.raspberrypi.org/app/uploads ... herals.pdf). So, may be a typo in the users manual (which mod needs to check ..
Note: DPI is not visible from the peripheral Manual ... so there is some inconsistency in the documentation)

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