Debian Wheezy on a ThinkPad 365X

Written 2014-08-06

Tags:Linux Open source Debian ThinkPad 

Intro

I've had this old ThinkPad for quite a while. I used to run Linux 2.6.8, but after the libata rewrite, debian wouldn't boot due to a missing root partition. Until today. Today I run debian stable.

Prerequisites

Hardware - Thinkpad 365X

  • Intel Pentium@120MHz(f00f bug and everything)
  • 8MB Integrated RAM(This can't do it alone)
  • 64MB expansion RAM(32MB should also work, 16MB would be sketchy)
  • 35MB total RAM recognized(try bios upgrade?)
  • 2GB CF card(super-cheap, much faster than contemporary spinny-disks)
  • IDE44<->CF adapter, approx $5 from Shenzen

Hardware - Other

  • USB<->CF adapter or USB<->IDE44 adapter, approx $5 from Shenzen
  • Computer with kvm/qemu

Software

Inserting the Disk in the VM Host

Since we're going to be working with raw disk IO, you'll need to unmount any automounting done when you connect the disk over USB to the VM host. Simply put, we don't want two OS kernels fighting for the same block device.

Creating a Virtual Machine image(optional, but recommended)

First, create a VM image of exactly the same size as your CF card or target hard disk. For QEMU/KVM, a file full of garbage is fine, or you can just rip the disk with dd using `dd if=/dev/sdX of=~/vmfilename.img bs=1M`.

Installing Debian in a Virtual Machine

KVM(or QEMU in a pinch) can be used to simulate a classic Pentium system, but not directly the one in the Thinkpad. `sudo {qemu or kvm} -hda {path to VM image or /dev/sdX} -cdrom {path to debian} -boot d -m 1024 -cpu pentium` Breaking it down:
  • sudo - run the command as root to allow qemu raw disk access. May also be needed for KVM(but not QEMU). Skip if using VM image with QEMU.
  • kvm - run a kernel-virtual-machine. Basically QEMU + hardware virtualization
  • qemu - run the old-school cpu emulator. Slower, but works on any host CPU, doesn't require root access
  • -hda - tell qemu/kvm where to find the disk image.
  • -cdrom - tell qemu/kvm where to find the CD image.
  • -boot d - tell qemu/kvm to boot from CDROM this time.
  • -m - Set VM RAM. In my case I used 1GB because it makes the installer a bit faster, but default also works.
  • -cpu - Set VM core type. In my case I set it to Pentium. This will cause the Wheezy installer to pick an i486-compatible kernel+libc
While working through the normal installer, here are some things to consider:
  • Old spinning disks are slow. Mounting partitions with 'noatime' or 'relatime' is quite helpful for this.
  • If you are low on disk space / ram, you will likely wish to install zero additional packages; I unchecked all the boxes. The complete desktop environment isn't really an option here either.
A note - if you use the advanced installer, we're going to rebuild an initrd anyways, and since qemu/kvm won't emulate the ThinkPad's IDE chipset, it doesn't make sense to strip it down in the installer because the virtualized installer will pick the wrong hardware. Once the install is complete, you may need to restart kvm/qemu, but changing "-boot d" to "-boot c", which will now boot from the emulated or USB disk.

Removing The Extras

This topic is best handled elsewhere. Removing daemons will save RAM, removing things in general will save disk space. The 365X is very limited by today's standards.

Install Your Favorite Packages

Now(while we have an emulated ethernet connection) is a good time to pull down any WiFi firmware you might need, as well as the pcmciautils package, and any other tools. Here's my list(455MB used/2GB total), less than 9MB RAM used after bootup:
  • sudo
  • cupt
  • htop
  • nload
  • hexedit
  • pcmciautils
  • linux-firmware-free
  • linux-firmware-nonfree
  • linux-wlan-ng
  • openssh-client
After installing everything, use "sudo apt-cache clean" to remove downloaded package installer files.

Building a New, Smaller Initrd

At least with 35MB of usable RAM, the default initrd won't fit. You might be able to do it with bios support for a 64MB stick. The last time debian had an initrd that did fit, it no longer contained the required ATA drivers for the 365X. So, to rebuild:
  1. Copy+rename the existing initrd alongside the current one. You'll find it in /boot/initrd-{somethingorother}
  2. edit /etc/initramfs-tools/modules to add "pata_legacy". If you want to be able to reboot in the VM, also add ata_piix.
  3. edit /etc/initramfs-tools/initramfs.conf to set "MODULES" to "dep"
  4. sudo update-initramfs -u
A word of warning for upgrades - the Jessie i686 kernel doesn't seem to have pata_legacy module, and I suspect the i486 kernel may not either.

Burning the Image to Target(required if using VM image, otherwise skip)

Burning the image back to the disk is just the reverse of ripping it. Flip the arguments on dd, taking care not to use the partition number.

Ejecting the Disk

Just run `sync`, then `eject /dev/sdX`, then wait for any lights to stop blinking, then unplug.

Booting up the 365X

Unplug power and battery, click the power button to make sure the board is drained, insert the card, replug power, hit switch.
It should just work. However, here's some of the problems I had along the way, in the order I had them, that should've been fixed by following the above instructions:
  1. Hung up in Grub - turns out Grub is just really slow on this box.
  2. Hung up loading initramfs - caused by initramfs too large for current RAM. The kernel used to give a nicer message about this. Fixed by removing unused modules in initramfs rebuild above.
  3. Hung up in (initramfs) prompt - caused by missing ATA driver pata_legacy. Fixed by initramfs rebuild above.

Volume of Spheres to Cubes Over Varying Dimensions.

Written 2014-07-06

Tags:Math n-Ball Hypercube Dimension Hypersphere 

As James Jolly said(approximately) to me, as the number of dimensions goes up, a normally-distributed dataset's points become closer together. To approximate it, draw a circle in a square, followed by a sphere in a cube, followed by a hypersphere in a hypercube. This relationship wasn't intuitively apparent to me, so I plotted it out.
polydimrat output

Some Intuition

To think recursively, each next-higher dimension contains an infinitely thin slice of the current dimension. For example, in three dimensions, a the area of a circle cut through a unit sphere by a plane of z=0 is the same area as a 2-dimesional unit circle. This is true all the way down - a 1-dimensional circle fills the 1-dimensional space from the leftmost to the righmost points on the 2-dimensional circle.

Intuition at the Equator

plot_3d

Intuition at z=-0.75

plot_3d_threeQuarters

But, we may notice that the ratio of circle-to-square in our slice is highest only in the middle(z=0). By varying from the center of our dimension-splitting subregion that ratio in the slice is always smaller. This is also true for the ratio of sphere-to-square in any two neighboring dimension sets(n->n+1). By approximating an integral, if the highest ratio in a dimensional space is the ratio in the lower dimensional space, and our integral averages over all the current space, then the ratio in the current space must go down, as being an average of ranges between 0 and the ratio of the previous space.

STREAM:UltraSPARC IIIi vs UltraSPARC T1

Written 2014-06-21

Tags:SPARC benchmark STREAM computing 

Today, I ran STREAM on my old router(Sun V210, 2x UltraSPARC IIIi) and my new one(Sun T2000, 1xNiagara T1).

Benchmark Overview

STREAM is a simple memory bandwidth benchmark. It conducts a series of operations on large vectors of variables and reports back on how long the operations took, as well as a double-check to ensure the results are correct. The tests are:
  • Copy: Y[] = X[]
  • Scale: Y[] = X[]*n
  • Add: Y[] = X[]+Z[]
  • Triad: Y[] = X[]*n+Z[]
The Copy test almost always gets optimized to a memcpy, which serves as a good reference for systems with weak FPU performance, or with no FPU at all. All other tests tend to make heavy use of any available FPU.

System Overview

V210

The V210 uses two UltraSPARC IIIi CPUs attached to DDR memory. Each IIIi supports a single core with FPU.

T2000

The T2000 uses a single UltraSPARC T1 CPU attached to DDR2 memory. The T1 supports four cores each with eight threads, but with only a single FPU. Effectively up to 32 independently schedulable threads. The T1 is also known for slow single-threaded performance, a design corrected in the T4 and newer CPUs.

STREAM Results in Megabytes/Second

Box: V210x1V210x2T2000x1T2000x32
Copy: 496.7 577.5 429.6 3492.9
Scale:498.3 568.0 261.2 1558.7
Add: 494.1 597.1 282.8 2133.4
Triad:419.3 579.5 220.9 1176.8

Single-Threaded Results

V210

What can I say? This router is getting old.

T2000

The T1's single-threaded results are bad - even worse than the IIIi(a 4 year older design). This could prove to be a problem, as in addition to routing, I'll need it to run a few mostly single-threaded game servers as well. More measurements required.

Relative Multi-Threading Improvement over Single-Threading

Box: V210x2T2000x32
Copy: 1.16 8.13
Scale:1.14 5.97
Add: 1.21 7.54
Triad:1.38 5.33

Multi-Threaded Results

V210

A little bit faster, but not a whole lot. This usually means that one thread is capable of nearly saturating the memory bus/controller, which is good - it implies that the penalty for the extra multithreading hardware is relatively cheap, although it could also mean your memory controller or cache just isn't very good.

T2000

This is where the T1 shines, with between 5.3x and 8.1x more bandwidth usage spread over 32 threads. What's interesting here, is that the overall improvement was greater than 4x(number of cores). This means that a hardware thread isn't capable of saturating the bandwidth for the local core, and so 8 or more threads will be required for saturating the chip's bandwidth and that may only occur if the kernel schedules them 2-to-a-core.

Detecting Exceptions on OpenBSD and MIPS

Written 2014-06-18

Tags:Interrupt MIPS Exception OpenBSD 

The MIPS processor exception handling sequence uses two reserved general-purpose registers, k0 and k1. When the exception occurs, the core jumps to the exception handler address, then using only k0 and k1, the handler must save enough state to handle the exception. To prevent information leakage from kernel-space to user-space, OpenBSD clears k0 and k1 to zero near the end of the exception handler. By populating k0 or k1 with a non-zero value, we simply need to poll one to detect when an exception occurs.

IT-24 Image Scraper Now Supports More Analyzers

Written 2014-03-16

Tags:AA-170 Ham Radio Antenna IT-24 WiFi HSMM RigExpert 

The IT-24 Image Capture tool has been updated to support AA-170 analyzers as well. The AA-170 analyzer uses a 128x64 1-bit display, a simpler image transfer protocol, and a slower baud-rate. The new baud-rate must be specified on the command-line.

Additionally, this software should work on several other RigExpert analyzers like the AA-30 and AA-54, and may work with AA-230 and AA-520 as well. If you have one of the above analyzers, I'd love to hear if it works.

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