Come on, you guys, stop talking about RISC/CISC already and tell him about the REAL A1 stuff, the A1 hardware!
The PPC processor chip is the next generation after the 680x0 CPUs that Commodore used. IBM and Motorola got together many years ago and developed a common design to compete with Intel's x86 range. Although the PPC range is still lagging behind the Intel range in sheer speed and performance, it was designed properly, rather than the patch-on-patch design of x86 CPUs. PPCs are made by IBM and Motorola, but most are soaked up by Apple for their Macs (so what remains for us is expensive).
On the A1 boards, as on x86 motherboards, the CPU is connected to the local memory through a "Southbridge", and to the PCI bus through a "Northbridge" chip (is that the right way around?). These chips (the "chipset" of the motherboard) handle the differing data and control protocols of the memory, PCI bus and CPU chip. Until about a year ago, there was no Northbridge for PPC that could handle the AGP bus that modern graphics cards demand. Then Mai brought out their "Articia" chipset for embedded PPC, with AGP support. Apple have their own chipset for the Macs, but it's not for sale.
The PPC is rather like the 68k series - lots of registers (32 integer, 32 floating point). It can operate in little- or big-endian mode, but in AOS4 I think it's being used in big-endian mode, like the 68k series.
The x86 Intel series processors are little-endian, which means that a multiple-byte number like 0x00001234 appears in memory as 34, 12, 00, 00. In a big-endian machine like the 68k, it appears as 00, 00, 12, 34. The main difference is the order that the hardware reads the memory addresses. But it makes it difficult to plug in devices designed for x86 and connect them to a CPU that's big-endian. Somewhere the data all has to be reversed.
Worse still, more complex devices like graphics cards have ROMs on board with their own initialisation code (written in x86 code,of course). Remember the auto-configure magic of the original Amigas?
The A1 firmware (BIOS, if you like) has a minimal x86 emulator in it, that can read the init code from a PCI device and emulate it on the PPC side, to get a graphics card up and running.
So a lot of work has been done to get to the stage where x86 PC hardware can be connected through a PCI/AGP bus, to a PPC CPU chip. Then software has to be written for the PPC to make all this new hardware work, before you can even start to think about interfacing Amiga software to the new hardware.
Fortunately, most of this work has now been completed. Limited quantities of the A1 boards are already out with low-level developers, running Linux and other metal-hitting software to get the interfacing right. Every week or so another device is made to behave in this new environment. The list of working hardware grows continually.
Other developers are working on the AOS4 software. It started out life as AOS 3.1, since Haage and Partner kept the sources to AOS 3.5.
So AOS 4 has been completely re-written for the PPC. It was a mess of C, BCPL, and assembler, poorly documented. Now, we are told, it's nearly all pure PPC, although some Workbench utilities are still in m68k code. They can stay that way, because a fast emulator has to be provided to run old software, anyway.
Much of the porting work has been performed on PPC add-ons like Cyberstorms and Blizzards, but now that real A1s are available, work continues on the real thing. We are told that AOS4 is in beta state on the new hardware. Third parties are writing graphics card drivers.
tony
