Behaviour of different eMMC areas?

Technical Support
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1

Does the behaviour for the different eMMC areas of the Linux BSP v2.7b4 boot area partition 1/primary eMMC boot sector, boot area partition 2 aka secondary eMMC boot sector and user area aka general purpose eMMC region differ w.r.t. reliability of data storage/flashing, etc. when flashed onto the Apalis TK1 2GB v1.2A? The areas use different partitions which make them behave differently from a configuration/formatting point of view. But is there something to be considered from a HW feature support point of view w.r.t. the eMMC locations they are written to?

This eMMC layout is from update.sh:

# The eMMC layout used is:
#
# boot area partition 1 aka primary eMMC boot sector:
# with cbootimage containing BCT and U-Boot boot loader and the U-Boot
# environment before the configblock at the end of that boot area partition
#
# boot area partition 2 aka secondary eMMC boot sector:
# reserved
#
# user area aka general purpose eMMC region:
#
#    0                      -> IMAGE_ROOTFS_ALIGNMENT         - reserved (not partitioned)
#    IMAGE_ROOTFS_ALIGNMENT -> BOOT_SPACE                     - kernel and other data
#    BOOT_SPACE             -> SDIMG_SIZE                     - rootfs
#
#            4MiB               16MiB           SDIMG_ROOTFS
# <-----------------------> <----------> <---------------------->
#  ------------------------ ------------ ------------------------
# | IMAGE_ROOTFS_ALIGNMENT | BOOT_SPACE | ROOTFS_SIZE            |
#  ------------------------ ------------ ------------------------
# ^                        ^            ^                        ^
# |                        |            |                        |
# 0                      4MiB      4MiB + 16MiB              EMMC_SIZE
2

The eMMC datasheet (THGBMHG7C1LBAIL) doesn’t contain any information about it. Seems like there is no difference.

3

Unfortunately this is not quite as well documented as one could wish for. The particular vendor’s eMMC data sheets do usually not mention resp. configuration/settings at all. However the Embedded Multi-Media Card (eMMC) Electrical Standard 5.1 aka JESD84-B51 mentions the following under section 6.2 Partition Management:

If the enhanced storage media feature is supported by the device, boot and RPMB Area Partitions shall be implemented as enhanced storage media by default.

As basically all newer eMMC parts support enhanced storage media features separate boot area partitions are implemented as enhanced storage media with write reliability features activated.

4

Hi Marcel, thanks a lot for that hint. Does this only affect the reliability of writing? Or does it affect behaviour during operation as well? (I mean despite of writing during operation.)

5

No, I would assume that internally the eMMC does use stronger ECC or even double block mirroring aka pSLC mode and what not to harden overall operation on those areas. This write reliability thing is basically a JESD84 naming thing whose exact implementation details are anyway left to resp. vendor’s discretion.

6

Thanks a lot for your detailed answer!

7

You are very welcome.

8

Hi Marcel, I was wondering whether the datasheet for the eMMC of the Apalis i.MX6Q is available? Also, if it is possible to activate write reliability on the other partitions, are there any detrimental effects to doing so?

9

Would you please ask a new question rather than hijacking an old one? Thanks!

10

No problem, I’ve asked it here

11

@Jimmy Thanks.