Kontron COMe-cP2020 - Manual (Page 90)

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COMe-P2020 User Guide
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6.4 U-Boot Access and Startup
Communication with U-Boot is achieved via a serial console configured for 115200 baud, 8N1, no hardware handshake.
Initially, U-Boot executes the commands defined in the environment variable “preboot”. Then, if not otherwise inter-
rupted, U-Boot pauses for the time defined in the environment variable “bootdelay” and then executes the statements
stored in the environment variable “bootcmd”. To gain access to the U-Boot command prompt, type in any single character
during the boot delay time.
If required, the boot delay function can be configured in such a way that even when the boot delay is set to “0” to have
characters, which are sent over the serial interface prior to the boot wait time, be recognized to allow operator interven-
tion in the boot process.
6.5 Working with U-Boot
6.5.1 General Operation
Most operations are carried out using the main memory as an intermediate step. It is not possible, for example, to boot a
kernel image directly from a tftp server. Instead, the kernel image is first loaded to memory and then booted from there
with another command.
The same is true when writing new contents to the SPI boot flashes.
This concept is very flexible since it separates the commands which handle the loading of data from the commands that
carry out actions like booting or programming flash devices.
6.5.2 Using the sconf Command
In previous board designs, DIP switches were used to configure the fabric interfaces. In response to evolving application
requirements, the “sconf” command has been designed to provide increased configuration flexibility.
The COMe-cP2020 is delivered with a default configuration for the external interfaces routed to the COM Express connec-
tors. If required, these interfaces may be configured via the “sconf” command according to the application requirements.
The factory default configuration for the COMe-cP2020 is as follows:
• “sconf” base configuration: 1 (PCIEx4 @2.5)
• eTSEC2 mode: RGMII
• eTSEC3 mode: RGMII
• Boot ROM location: SPI
To obtain information about the currently active configuration, invoke the “sconf info” command.