Timeout
waiting for
answer?
MMC / SD detection
SD device
MMC device
No response received
Send CMD55
Send ACMD41
Response received
Send CMD1 command
Timeout
waiting for
answer?
Yes
No
No device detected
Functional Description
Another point to note is the difference in the arguments to CMD1 between MMC0 and MMC1. At first the
ROM queries the card with CMD1, ARG = 0, to get the OCR from the card. On MMC0, the response from
the card is simply reflected back to the card as the argument for all subsequent CMD1, till the card is in
the READY state. On MMC1, Bit30 of the response received from the card is set to 1 by the ROM, and
this modified value is used as the argument for subsequent CMD1. This is done to indicate to the card that
the ROM supports sector addressing. This mode might not be compatible with older (older than v4.4)
versions of cards.
Figure 26-18. MMC/SD Detection Procedure
As previously mentioned the contents of an MMC/SD card may be formatted as raw binary or within a FAT
filesystem. eMMC / eSD devices only support raw mode. The ROM Code reads out raw sectors from
image or the booting file within the file system and boots from it.
26.1.7.5.5 MMC/SD Read Sector Procedure in Raw Mode
In raw mode the booting image can be located at one of the four consecutive locations in the main area:
offset 0x0 / 0x20000 (128 KB) / 0x40000 (256 KB) / 0x60000 (384 KB). For this reason, a booting image
shall not exceed 128KB in size. However it is possible to flash a device with an image greater than 128KB
starting at one of the aforementioned locations. Therefore the ROM Code does not check the image size.
The only drawback is that the image will cross the subsequent image boundary.
The raw mode is detected by reading sectors #0, #256, #512, #768. The content of these sectors is then
verified for presence of a TOC structure as described in
. In the case of a GP Device, a
Configuration Header (CH) must be located in the first sector followed by a GP header. The CH might be
void (only containing a CHSETTINGS item for which the Valid field is zero).
26.1.7.5.5.1 Configuration Header
For Raw Mode, the Configuration Header should be formatted as follows:
4131
SPRUH73H – October 2011 – Revised April 2013
Initialization
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