UM1535 datasheet(11/39 Pages) STMICROELECTRONICS

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UM1535

Working with pre-flashed software

Doc ID 023036 Rev 2

11/39

There is a wide choice of file system standards for Flash memories in the Linux world (for

example, CRAMFS, JFFS2, YAFFS2, LogFS, UBIFS).

The pre-flashed software is based on the most commonly used standard, namely JFFS2.

The main advantage of JFFS2 is the built-in support for compression. It is also the most

consolidated file system, while generally not providing the best performance in terms of

booting time.

2.3

Booting up to the Linux prompt

To boot Linux just power up the board. You then see the bootloader messages and prompt.

If you press space key in this phase, you stop the bootloader execution and display the U-

Boot command prompt (see next section). Instead, wait for a few seconds while the Linux

kernel is loaded and launched. Progress is displayed by a sequence of kernel boot

messages. The root filesystem is mounted automatically, the system shell is run and a

prompt appears when it is ready to accept commands.

The pre-flashed filesystem provides a default set of system commands and runtime

libraries.

System commands are the familiar basic utilities mainly provided to support the

development and debugging stages. They are all stored under standard Linux paths. They

may not be strictly needed in a final product, however their small size allows them to be kept

in production devices without a significant penalty in terms of memory footprint.

As is typical for embedded Linux environments, STLinux uses BusyBox, an open source

program combining tiny versions of many common user-space Linux utilities into a single

small executable, an important factor when minimized Flash footprint is required.

BusyBox has been developed with size-optimization and limited resources in mind, for this

reason the available commands typically have fewer options than their full-featured GNU

counterparts. However, the most important options are still available with all the functions

needed for developing and testing embedded products.

As well as the features of BusyBox, a number of additional executable programs are also

included.

In addition to playing with commands, it can be also helpful to explore the Linux standard

/proc pseudo-filesystem. This subtree contains user-accessible entries that pertain to the

runtime state of the kernel and, by extension, the executing processes that run on top of it.

The "pseudo" term is used because the proc filesystem exists only as a reflection of the in-

memory kernel data structures it displays. This is why most files and directories within /proc

are zero bytes in size.

In practice, the proc file system is intended to be populated at runtime with system

information and statistics. Proc files may be either read-only or read-write. Each numerically

named directory within /proc corresponds to the process ID (PID) of a process currently

executing on the system. This part of the proc file system totally depends on the runtime

state of the target. Each numeric entry contains subfiles that provide process-specific

information. The other (non-numeric) entries describe some aspects of kernel operation.

Some of the common user commands performed on the proc file system are:

# cat /proc/version

Displays full Linux kernel version information

# cat /proc/sys/kernel/osreleaseDisplays Linux kernel release

# cat /proc/sys/kernel/version

Displays Linux kernel build date and time

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