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L4Re Servers

Here you shall find a quick overview over the standard services running on the L4Re Microkernel.

# Sigma0, the Root Pager

Sigma0 is a special server running on L4 because it is responsible of resolving page faults for the root task, the first useful task on L4Re. Sigma0 can be seen as part of the kernel, however it runs in unprivileged mode. To run something useful on the L4Re Microkernel you usually need to run Sigma0, nevertheless it is possible to replace Sigma0 by a different implementation.

For more details see Sigma0, the Root-Pager

# Moe, the Root Task

Moe is our implementation of the L4 root task that is responsible for bootstrapping the system, and to provide basic resource management services to the applications on top. Therefore Moe provides L4Re resource management and multiplexing services:

- Memory in the form of memory allocators (L4Re::Mem_alloc, L4::Factory) and data spaces (L4Re::Dataspace)
- Cpu in the form of basic scheduler objects (L4::Scheduler)
- Vcon multiplexing for debug output (output only)
- Virtual memory management for applications, L4Re::Rm

Moe further provides an implementation of L4Re name spaces (L4Re::Namespace), which are for example used to provide a read only directory of all multi-boot modules. In the case of a boot loader, like grub that enables a VESA frame buffer, there is also a single instance of an L4Re graphics session (L4Re::Goos).

To start the system Moe starts a single ELF program, the init process. The init process (usually Ned, see the next section) gets access to all resources managed by Moe and to the Sigma0 root pager interface.

For more details see Moe, the Root-Task.

# Ned, the Default Init Process

To keep the root task free from complicated scripting engines and to avoid circular dependencies in application startup (that could lead to dead locks) the configuration and startup of the real system is managed by an extra task, the init process.

Ned is such an init process that allows system configuration via Lua scripts.

For more information see Ned.

# Io, the Platform and Device Resource Manager

Because all peripheral management in L4Re is done in user-level applications, there is the need to have a centralized management of the resources belonging to the platform and to peripheral devices.

This is the job of Io. Io provides portable abstractions for iterating and accessing devices and their resources (IRQ's, IO Memory...), as well as delegating access to those resources to other applications (e.g., device drivers).

For more details see Io, the Io Server.

# Other Servers

The following additional server package are available on top of the core L4Re environment.

- Rtc, the Real-Time Clock Server

  is a simple multiplexer for real-time clock hardware on your platform.

- fb-drv, the Low-Level Graphics Driver

  provides low-level access and initialization of various graphics hardware. It has support for running VESA BIOS calls on Intel x86 platforms, as well as support for various ARM display controllers. fb-drv provides a single instance of the L4Re::Goos interface and can serve as a back end for the Mag server, in particular, if there is no graphics support in the boot loader.

- l4vio_net_p2p, a virtual network point-to-point link
- l4vio_switch, a virtual network switch
- Uvmm, the virtual machine monitor
- RTC driver

- Mag, the GUI Multiplexer

  Our default multiplexer for the graphics hardware is Mag. Mag is a Nitpicker (TODO: ref) derivate that allows secure multiplexing of the graphics and input hardware among multiple applications and multiple complete windowing environments.

- Sigma0, the Root-Pager
- Cons, the Console Multiplexer