PowerPC Linux Box

The Idea

The CHRP Specification

The CHRP specification details the capabilities in terms of hardware and software interfaces that must be present on a system that is to be called CHRP-compliant. The specification has many optional enhancements (power management, SMP, ...), but the basic requirements are quite small, yet powerful enough to let a full-blown OS like Linux run on it. Note specifically that no need for display, keyboard, mouse or specific hard disk interface (IDE, SCSI) is required. Some kind of boot device is of course needed, but this could in principle be a solid state disk (Flash). Support for many of the devices known from the PC world is encouraged (PS/2 keyboard & mouse, VGA graphics card, Ultra DMA/33 IDE Controllers and much more), and is directly supported by Linux when present (and implemented according to the CHRP specification, of course).

The Technology

Motorola has made a so-called Yellowknife X4 ATX-sized reference design that incorporates a socket for a PowerPC CPU (604/740/750), SDRAM, boot Flash, PCI Bridge (MPC106), PCI sockets, ISA bus & sockets. This board is available to developers only at an uncompetitive price for evaulation of the PowerPC processors and the architecture. Furthermore, this board is not even CHRP-compliant, as it does not implement the OpenPIC interrupt controller. But significant inspiration can be gained from the design.

The Questions

As should be apparent from the above, it is possible to build a powerful PowerPC system based on the minimal subset of the CHRP specification, using basically only the CPU, the North Bridge, a Flash device and a SDRAM array. By adding some more components, full legacy ISA support can be added at the cost of more design time, more real estate (big PQFP's, buffers and connectors) and more complicated PCB layout and production (but the Yellowknife X4-design is said to be only a 4-layer board!)
A lot of hardware design details must be cleared: On the software front we have:

The Decision

To my knowledge, no CHRP platform is easily commercially available for end users. In the PowerPC world it seems that the focus is either on the Apple PowerMAC desktops or the embedded market. The apperance of a powerful operating system like Linux can change this! Because of the portability of Linux and the applications running on it, the foundation for a desktop system not based on the Windows/i386 or the Apple OS/PPC is suddenly possible. With an easily scalable system, that has SMP-support built-in, a whole range of products/projects emerge, ranging from complete multiprocessor ATX-sized motherboards with PCI and ISA buses and peripherals for end-user desktops to small match-box sized embedded boxes, all running Linux.

Bear in mind that all this could also in principle be done on an Alpha-processor based system. The Alpha is indeed a powerful processor architecture, maybe even more powerful than the PowerPC, but seen from the view of a kitchen-table project, the PowerPC world seems much more within reach in terms of support and availability of the necessary components and circuitry.

If you don't believe that you can change the world, what are you doing here anyway?

Background Literature