[dinartem]

One challenge was that while I started working on the Xbox 360 about three years before it would ship, we knew that the custom CPU would not be available until early 2005 (first chips arrived in early February). And there was only supposed to be one hardware spin before final release.

So I had no real hardware to test any of the software I was writing, and no other chips (like the Apple G5 we used as alpha kits) had the custom security hardware or boot sequence like the custom chip would have. But I still needed to provide the first stage boot loader which is stored in ROM inside the CPU weeks before first manufacture.

I ended up writing a simulator of the CPU (instruction level), to make progress on writing the boot code. Obviously my boot code and hypervisor would run perfectly on my simulator since I wrote both!

But IBM had also had a hardware accelerated cycle-accurate simulator that I got to use. I was required to boot the entire Xbox 360 kernel in their simulator before I could release the boot ROM. What takes a few seconds on hardware to boot took over 3 hours in simulation. The POST codes would be displayed every so often to let me know that progress was still being made.

The first CPU arrived on a Friday, by Saturday the electrical engineers flew to Austin to help get the chip on the motherboard and make sure FSB and other busses were all working. I arrived on Monday evening with a laptop containing the source code to the kernel, on Tuesday I compiled and flashed various versions, working through the typical bring-up issues. By Wednesday afternoon the kernel was running Quake, including sound output and controller input.

Three years of preparation to make my contribution to hardware bring-up as short as possible, since I would bottleneck everyone else in the development team until the CPU booted the kernel.

[Zeetah]

You have an awesome memory, Dinarte!

Eric Mejdric from IBM called on Friday and said we have the chips, when are you guys getting here?

I took a red eye that night and got to Austin on Saturday morning.

We brought up the board, the IBM debugger, and then got stuck.

I remember calling you on Sunday morning. You had just got a big screen TV for the Super bowl and had people over and in-between hosting them you dropped us new bits to make progress.

I think Tracy came on Sunday or Monday and with you got the Kernel booted.

Good times!

This is Harjit by the way.

Edit: added super bowl.

[saturn8601]

OMG Harjit! I saw you in the documentary! You and the entire team are total rockstars! I just cannot fathom ever being in a position to design something that provided so much joy and happy core memories to countless people around the world...you guys did it!

Just the thought of how many people you touched with your work....just amazing! :)

Had a question if you don't mind: Can you talk about the thought process behind the power supply design? Its very large even in the super slim models. Were you following a specific design driven by the hardware architecture or were there other reasons? I always wondered about that.

[dinartem]

Actually Tracy never made it to Austin. He was going to fly in later in the week to continue bring-up, but since we were done by Wednesday, we just sent the chips to Redmond and he continued there. He was of course always available on the phone to answer my kernel questions I had.

[markus_zhang]

This is really some blast from the past. Can you please shed more light on the simulator? Is it interpretation or JIT? But then I realize XBOX uses Pentium III, so maybe virtualization? Edit Sorry it was XBOX 360 so it's not Pentium.

As someone who recently got interested in emulation and wrote two lc-3 emulators, would really love to learn from the masters.

[brokenmachine]

Kick ass. This kind of post is why HN is the best.

[fragmede]

damn, that's bad ass. did that simulator run on a Windows system or was it something more esoteric?

[dinartem]

I called the simulator Sbox and it was just a simple console app. I didn't implement the GPU, so no graphics just the hypervisor and kernel and some simple non-graphics apps. I made it so that you could build the Xbox 360 kernel on your windows machine, then just run sbox.exe and it would automatically find the just built kernel image targeting the PPC64 and boot it. Then if you typed control-C it would drop into the kernel debugger as a sub process, and you could poke around at the machine state as if it were the real Xbox hardware, showing all the PPC instructions and registers. It was a lot of fun writing it, and quite useful.

[kridsdale1]

This is the coolest HN post I’ve read in months.

Cheers.

[cbanek]

Small world! I worked on Yellow Door / Golden Gate automation for releasing 360 titles and patches to prod, and the beta group / KDC service code.

[saturn8601]

You sir are an inspiration! I am but a mediocre Angular developer and reading this has me in complete awe! The kind of drive you must have had to get this done well I dont know how people manage to do it but it is so cool to see! :)

[n144q]

> we knew that the custom CPU would not be available until early 2005

Sounds a little bit like the situation with Xbox Series? The SDKs were released late because Microsoft was waiting for certain features in AMD APU

[bananaboy]

Amazing! Thanks for sharing! What sort of things are you working on now?