Category: Embedded

uClinux is a popular port of the Linux operating system to processors without a MMU (Memory Management Unit). Kernel versions 2.0.x, 2.4.x, and 2.6.x are supported to varying degrees on numerous architectures.

The uClinux distribution contains the following main components: the uClinux kernel, various libraries and numerous linux utilities. In this article some of the tasks that need to be done to port the uClinux kernel to a new architecture are examined. The information is specific to the 2.4.x uClinux kernel and the Samsung S3C44B0X, a 32-bit processor with an ARM7TDMI core.

The latest uClinux distribution uClinux-dist-20040408, can be downloaded from here. The ELF ARM7 toolchain for uClinux can be downloaded from here.

Three are three main levels where porting is required. In the case where the processor core is not supported, a new architecture will have to be added in uclinux/linux-2.4.x/arch/. In our case, support for the ARM7TDMI architecture is already present in uclinux/linux-2.4.x/arch/armnommu/ considerably reducing the effort required to port uClinux to the s3c44b0x processor. At the second level, support for the particular processor (machine) is to be added using processor specific knowledge such as registers etc. Finally, support for the board containing the processor and peripherals need to be added. This will include adding support for devices on the board that are not yet supported by linux, or configuring existing device drivers.

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This article describes the steps to be followed to debug applications on embedded ARM7TDMI processors using the GNU Debugger 'GDB' and gdbserver.

Embedded systems typically have memory constraints that restrict the size of executables (with debug information) and debuggers stored in ram. A stripped executable binary of much smaller size is usually placed on the target board, while the executable with debugging information remains on the host development system. Similarly since GDB is a large and sophisticated debugger, a light-weight control program gdbserver was created to be run on the target system.

gdbserver is executed along with the stripped application on the target machine. GDB is loaded on the host system along with the unstripped application, containing debug symbols. GDB communicates with gdbserver via a serial port or TCP/IP to provide a full-fledged debugging environment. In this article a GUI front-end debugger, Data Display Debugger 'DDD' is used.

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Random notes on the installation of Wonka, Kaffe, PCSC-lite, and Java Native Interface on ARM linux systems.

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During uClinux development, one of the most useful tools is a kermit download utility. Most bootloaders support download of binary images on to their targets via the Kermit protocol on a serial line. In windows the program Hyperterminal may be used to send the file from a host. For unix systems Columbia University released a free program, G-Kermit CU, which can be called by Minicom to perform a kermit transfer.

The following patch allows G-Kermit CU to function as a standalone program, eliminating the need of a terminal program such as Minicom.

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This article details the steps that need to be followed to add a kernel module to the uClinux build process.

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This article details the steps that need to be followed to add a user application to the uClinux build process. Upon building the uClinux distribution, the executable is created and copied to the romfs directory which is included with the final image. After the target board boots up, the binary may be executed from the rom filesystem.

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