First Look at an Apple G4 with the Altivec Processor
When I first read about Apple's plans to develop a G4-based personal computer, I didn't even know what a G4 was. Supercomputer performance? Processing in the GFlops? How could this be? G4, also known as the Motorola 7400, is the processor with the AltiVec unit. AltiVec is the trade name of the vector processing unit found in this new line of PowerPC processors. Motorola has also announced the 7410 and the 7450, which feature an L2 cache on the die, a large backside L3 cache, a faster processor core and a deeper, seven-stage pipeline.
The AltiVec unit is an enhanced integer or floating processing unit. It provides a new 128-bit processing unit, 32 vector registers and over 160 new instructions that allow for the processing of data in a pipeline. These provide a tremendous opportunity to move data through the processor.
After a description like that, who wouldn't want to have one of these at home? I'm not a Macintosh aficinado nor do I care for Windows very much. When I read about the work that Cort Dugan, Paul Mackerras, Ben Herrenschmidt and many others had performed porting Linux to PowerPC (PPC) I was sold. After all, this sounded like an opportunity to try something new and challenging, learn a little (or a lot) and get faster numbers from my distributed.net client (some of the reasons I started using Linux last millennium).
My hardware is an Apple dual-G4/450MHz PowerPC with 512MB RAM. It comes with a 30GB Quantum Fireball IDE drive, a CD/DVD-ROM, two IEEE-1394 (Firewire interfaces), 100Mbps Ethernet and more USB hubs than you can shake a stick at. The keyboard and mouse are both USB devices. Apple calls this a New World machine. Although this sounds like a marketing term, “New World” is used to describe Apple hardware where the boot ROM is stored in software (as opposed to “Old World” machines where boot management software was stored in a PROM).
The Linux distribution I chose to install was Yellow Dog Linux. I don't know what finally pushed me in that direction, given that there is more than one choice—SuSE, LinuxPPC and Yellow Dog Linux immediately come to mind. YDL is based on Red Hat, so it's not too unfamiliar.
YDL is provided by Terra Soft Solutions. While Terra Soft provides another distribution, Black Lab Linux, YDL is the entry point solution for the common user. I downloaded the two ISO images of YDL Champion Server 1.2.1 from one of Terra Soft's mirrors. The first is the installation CD; the second CD is known as “Tasty Morsels”. It provides a rescue image and some additional software for the PPC. I burned these images with cdrecord on my SuSE/i386 box and then wondered what I had.
After I read the YDL installation guide I had some idea. The guide suggested I use yaboot, “yet another boot loader”. yaboot needs to live on an HFS (native Mac) partition so I needed to create one using the Mac system software.
Here are the steps I used to reinstall Mac OS9 and then install Linux:
Create an HFS partition (4GB) for yaboot (and OS9).
Reinstall OS9 from distribution CDs.
From the CS 1.2.1 CD, copy yaboot, yaboot.conf and vmlinux.gz to the system folder.
yaboot.conf looks and feels a lot like lilo.conf. There are sections for each image with an area to provide a label so that when yaboot boots, the user can Tab to see the names of the kernel configurations and then select one at the prompt. Familiar stuff, but I had to modify yaboot.conf as shown below.
Here I should digress a bit about Open Firmware. Open Firmware, defined under IEEE 1275, is a specification for providing open support for firmware. This was one of the first interesting areas of my new Apple hardware explorations. I didn't see Open Firmware until I needed to. Upon booting the Mac an 880Hz tone sounds to indicates that your system just passed a hardware POST and is preparing to boot an operating system. At this point the booting process can be stopped by pressing and holding the Command-Opt-O-F keys. If all goes well the following greeting is displayed:
Apple PowerMac 3,3 3.4f1 BootROM built on 08/08/00 at 22:02:19 Copyright 1994-2000 Apple Computer, Inc. Welcome to Open Firmware. To continue booting, type "mac-boot" and press return To shut down, type "shut-down" and press return ok 0 > _
The 0 > is a prompt. OF is, at its heart, a Forth interpreter. Forth is a stack-based language. To obtain a sense of this, type the following at the prompt:
0 > 3 [RETURN] 1 > 4 [RETURN] 2 > + [RETURN] 1 > . [RETURN]and you will get the resulting:
0 > 7The first command pushed “3” on the stack. The prompt displays the number of items on the stack before the “>”. Then I placed “4” on the stack and told the interpreter to add the results. Now there was only one item on the stack. The “.” operator pops the first value off of the stack and displays it.
You can see quite a bit about your hardware from here. For example, to see the default boot configuration of your machine type the following at the prompt:
0 > printenv
Listing 1 shows the built-in environment variables and their defaults.
Another good bit of information from your PPC can be derived from the command devalias. Enter this command at the prompt and press the Return key. Pay attention to the value for hd. That is the hardware address of your first IDE hard drive. hd is an alias for the entire address displayed via printenv.
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