BeagleBoard XM C2, Справочное руководство

Страница: 85 / 163

REF: BB_SRM_xM
BeagleBoard-xM System
Reference Manual
Revision C2
Page 85 of 163
P26,R27,R25
7.15.3 Card Detect
When a card is inserted into the connector, the
Card Detect pin is grounded. This is
detected on pin P12 of the TPS65950 . An interrupt, if enabled, is sent to the processor
via the interrupt pin. The SW can be written such that the system comes out of sleep or a
reduced frequency mode when the card is detected.
7.15.4 Booting From SD/MMC Cards
The ROM code supports booting from the microSD cards with some limitations:
o
Support for SD cards compliant with the Multimedia Card System Specification
v4.2 from the MMCA Technical Committee and the Secure Digital I/O Card
Specification v2.0 from the SD Association. Including high-capacity (size >2GB)
cards: HC-SD and HC MMC.
o
3-V power supply, 3-V I/O voltage on port 1
o
Initial 1-bit MMC mode, 4-bit SD mode.
o
Clock frequency:
– Identification mode: 400 kHz
– Data transfer mode: 20 MHz
o
Only one card connected to the bus
o
FAT12/16/32 support, with or without master boot sector (MBR).
The high-speed microSD host controllers handle the physical layer while the ROM code
handles the simplified logical protocol layer (read-only protocol). A limited range of
commands is implemented in the ROM code. The MMC/SD specification defines two
operating voltages for standard or high-speed cards. The ROM code only supports
standard operating voltage range (3-V). The ROM code reads out a booting file from the
card file system and boots from it.