Phytec phyCORE-OMAP44 Series, Руководство по оборудованию

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phyCORE-OMAP44xx Part I: PCM-049/phyCORE-OMAP44xx System on Module
L-760e_1 © PHYTEC Messtechnik GmbH 2012 41
1.5 System Configuration and Booting
Although most features of the OMAP44xx microcontroller are configured and/or programmed during the
initialization routine, other features, which impact program execution, must be configured prior to
initialization via pin termination.
The system start-up configuration includes:
• Clock configuration
• Boot device order configuration
During the reset cycle the operational system boot mode of the OMAP44xx processor is determined by the
configuration of eight SYSBOOT pins sys_boot[7:0]. Pins sys_boot[5:0] are used to select interfaces or devices
for the booting list, while pins sys_boot[7:6] select the OMAP clock source configuration. All eight pins are
sampled and latched onto the SYSCTRL_GENERAL_CORE.CONTROL_STATUS[7:0] SYS_BOOT register bit field
during the execution of the ROM code.
The internal ROM code is the first code executed during the initialization process of the OMAP44xx after POR.
Besides the selection of the system clock source (based on the configuration of pins sys_boot[7:6]), the ROM
code detects which boot devices the controller has to check by using the sys_boot[5:0] pin configuration.
For peripheral boot devices, the ROM code polls the communication interface selected , initiates the download
of the code into the internal RAM and triggers its execution from there. Peripheral booting is normally not
applicable after a warm reset. For memory booting, the ROM code finds the bootstrap in permanent memories
such as NAND-Flash or SD-Cards and executes it. Memory booting is normally applicable after a cold, or a warm
reset. Please refer to the OMAP44xx Reference Manual for more information.
A configuration circuitry (pull-up and pull-down resistors connected to sys_boot[7:0]) is located on the
phyCORE module, so no further settings are necessary. The boot configuration of pins sys_boot[5:0] on the
standard phyCORE-OMAP44xx module with 512MB NAND Flash is ‘
0b111001 ’. Consequently, the system tries to
boot from NAND-Flash first, and, in case of a failure, successively from USB, UART and MMC1. Pins sys_boot[7:6]
are factory-set to ‘
0b00 ’, meaning that the on-chip oscillator is selected as system clock source.
The on-board configuration circuitry of sys_boot[5:0] can be overwritten by pull-up, or pull-down resistors
connected to the boot configuration pins (X1C57 - X1C59, X1D57, X1D58 and X1D60) of the phyCORE-OMAP44xx.
The following tables show the different boot device orders, which can be selected by configuring the six boot
configuration pins, X_BOOT[5:0] of the phyCORE-OMAP44xx. Please note that only the useful configurations are
listed in the tables. For a complete list of the OMAP44xx boot modes please refer to the Texas Instruments
OMAP44xx Reference Manual.
The first table lists the booting device order when it is preferred to boot from memory type devices. This mode
is selected when sys_boot[5] is tied high. The second table lists the booting device order when it is preferred to
boot from peripheral-type devices. This mode is selected when sys_boot[5] is tied low.
Note:
Only permanent booting devices (marked in bold ) are put on the booting list in case of a warm reset, as
peripheral booting is normally not applicable after a warm reset.