Functional Description
Table 26-27. FAT Entry Description
FAT12
FAT16
FAT32
Description
000h
0000h
?0000000h
Free Cluster
001h
0001h
?0000001h
Reserved Cluster
Used Cluster; value points to
002h-FEFh
0002h-FFEFh
00000002h-?FFFFFEFh
next cluster
FF0h-FF6h
FFF0h-FFF6h
?FFFFFF0h-?FFFFFF6h
Reserved values
FF7h
FFF7h
?FFFFFF7h
Bad Cluster
FF8h-FFFh
FFF8h-FFFFh
?FFFFFF8h-?FFFFFFFh
Last Cluster in File
Note: FAT32 uses only bits [27:0], the upper 4 bits are usually 0 and should be left untouched.
When accessing the Root Directory for FAT32, the ROM Code just starts from the Root Directory Cluster
entry and follows the linked chain to retrieve the clusters.
When the booting file has been found, the ROM Code buffers each FAT entry corresponding to the file in
a sector way. This means each cluster is translated to one or several sectors depending on how many
sectors are in a cluster (BPB_SecPerClus). This buffer is used later on by the booting procedure to access
the file.
26.1.7.5.8 Pins Used
The list of device pins that are configured by the ROM in the case of MMC boot mode are as follows.
Please note that all the pins might not be driven at boot time.
Table 26-28. Pins Used for MMC0 Boot
Signal name
Pin Used in Device
clk
mmc0_clk
cmd
mmc0_cmd
dat0
mmc0_dat0
dat1
mmc0_dat1
dat2
mmc0_dat2
dat3
mmc0_dat3
Table 26-29. Pins Used for MMC1 Boot
Signal name
Pin Used in Device
clk
gpmc_csn1
cmd
gpmc_csn2
dat0
gpmc_ad0
dat1
gpmc_ad1
dat2
gpmc_ad2
dat3
gpmc_ad3
26.1.7.6 SPI
SPI EEPROMs or SPI flashes have an EEPROM or NOR flash backend and they connect to the device
using the serial SPI protocol.
These devices typically operate in three stages: the command stage, the address stage and the data
transfer stage. The command is usually an 8 bit value followed by the address (depending on the size of
the device) followed by the data to be read or written.
Because of the need for fewer pins, these devices are comparatively inexpensive, easy for board layout,
and are the devices of choice when cost, complexity and form factor are critical considerations.
4141
SPRUH73H – October 2011 – Revised April 2013
Initialization
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