Dream Distro: Xen Debian Wrapped Windows (DubDubOS?)

There are a lot of linux distributions and I’ve used and tried out many of them over the years. I started with ubunto, then I got into elementaryOS, then centOS, debian, qubes, and then back to debian. I’ve tried parrotOS, openSUSE, and tails, but never used any of those as a main system. My current favorite is debian with gnome due to speed and compatibility with a huge pool of precompiled software packages.

What I want to talk about here is what my dream linux distribution would be like. What I want is a system which grants access to all of the software of windows and debian. Qubes can do this, of course, but is more secure and less fast than what I’m after. What I’m looking for is a distribution that loads a xen hyperviser with a debian dom0 system and a single windows hvm. The distro installs xen and the debian dom0 with desktop flavor of the users choice, then sets up an HVM and prompts the user to load the windows install disk, and installs that.

The key to the distro is to control software packages to keep the virtual system from breaking, and to optimize memory and cpu use balancing to insure the best performance (though this is primarily a goal of the xen developers). The distro must provide fast and simple screen switching from dom0 debian to hvm windows, and permit maximal hardware usability in the hvm and dom0. Finally, the dom0 home directory should be shared to the hvm as a mountable drive. Does the HVM have to be Windows? No, but that should be the main goal of the project, as it is the greatest need of the user.

Watt Ave Might As Well Be The Wild West

A huge road, three lanes on both sides from I80 to 50, passing right through densely populated residential and commercial areas, Watt Ave sees heavy traffic every day with the high speed limits only controlled by traffic congestion.

In addition to all this, large sections of Watt have no lighting (where it passes through residential areas) and the road largely lacks surveillance.

Given the recent eggy attack on my person from a moving vehicle, it’s obvious that having the high speed limit road running next to pedestrian walkway poses a potentially lethal risk to pedestrians. I’m in favor, therefore, of reducing the maximum speed limit to 30 mph on Watt from 50 to I80 and installing roadway surveillance with license plate capture around the intersections, or, alternatively, installing protective barricades between the road and walkways.

Egg welt

Looks like the egg struck me with it’s long side. Sheriff’s deputy says he can’t do anything because I wasn’t memorizing the make, model, and license plate of every oncoming car on the 3 lane northbound side of Watt Ave. This rings false, given the intersection camera pointed towards the Watt and Whitney bus stop where I was hit, and additional cameras at subsequent intersections northbound from there on Watt. (The incident occurred around 9:30pm on 9/21.) It’s assault, of course, and there are no circumstances in which I wouldn’t want charges pressed for this. The question is what measures can I take to protect myself?

Sulfur hexaflouride is the news.

SF6 is known in the utility industry as a dielectric material, but what is meant by that is that it is a material that can withstand high electric fields. Air can withstand electric fields around 30kV/cm, with some variance due to humidity and pollution, and SF6 can withstand 3 times that. Another common dielectric media in the high voltage industry is mineral oil which has a dielectric strength of up to 5 times that of air.

SF6 is mainly used in circuit breakers and gas insulated substations. SF6 permits these devices to be much smaller and lighter. Air insulated high voltage circuit breakers are theoretically possible, but would be massive and would perform differently depending upon weather conditions. Mineral oil circuit breakers were commonly installed before the invention of SF6 breakers, but these devices had to be large and heavy (10-20 times heavier than their SF6 counterparts), and had to contain a lot of heavy flammable oil. These characteristics that I’m describing are for dead tank circuit breakers, which have an outer shell that is grounded. Circuit breakers can also be “live tank” which permits a much lighter design. These are more difficult to maintain and require separate current transformer instruments which add more cost, but are not nearly as much as the difference between a live tank oil breaker and a dead tank oil breaker.

Gas insulated substations have all of the equipment of an air insulated substation but can be built much smaller in areas like cities that don’t have the necessary clearances for an open air station. Something similar to GIS can be done with mineral oil, but the weight, and therefore the necessary structural strength and cost increase by large factors.

In theory, it is possible to start to move away from SF6 technologies and return to mineral oil, but replacement of all of the currently in service SF6 devices would take decades and cost hundreds of millions to billions of dollars. The most cost effective method would be to use live tank oil circuit breakers, which would require less improvements to civil works like foundations and would require the least additional oil containment and fire wall additions. The problem is that this technology is not really being built anymore, as the industry has moved to the more efficient SF6 devices.

If one wanted to go with something new, nitrogen gas insulation is a reasonable alternative, Nitrogen is only a little stronger than air as a dielectric, but if it is in an enclosed tank with high purity, then none of the variances that would occur in open air would need to be accounted for and a reasonably sized design, but still much larger and more expensive than SF6, could be developed.

My weekend exercise.

For the past several weekends I’ve been hiking up this canyon. It’s a little over 3.5 miles with 2.5 miles of gentle slope and one grueling high slope mile. It’s had some pleasing health benefits, and the view’s not so bad.

Ideal Zener

Zener diodes are handy devices which can be inserted into a circuit in reverse to clamp voltages to desired levels. But like all circuit components, Zener diodes do nor exhibit ideal behavior in all circumstances. The zener voltage varies significantly based upon temperature and through current, for instance. Thus, if one wants to use a zener diode to protect a low voltage, sensitive chip from over voltage on VDD, there are some important considerations. Assuming we have a 3.3V VDD and we select a 3.3Vz Zener diode. The diode Vz will increase with through current, but will decrease with increasing temperature. It is easy and wise to eliminate the current variability by using overcurrent protection devices like PPTC fuses, sized such that current through the zener diode does not exceed the power dissipation limit of the component nor cause the Vz to rise above the voltage maximim of the chip to be protected, whichever of those occurs first as current rises.

A more difficult to handle concern is the tendency of the zener voltage to decrease with temperature. If the curcuit is designed to operate in a wide range of temperatures, then the actual zener voltage has to assessed for all of those temperatures, most crucially to insure that the reduced zener voltage does not fall below the minimum voltage required by the chip, and that there are no other negative effects from reduced VDD (such as how it affects adc reference or digital output voltage).

In extreme cases, where zener protection is needed, but zener voltage variance is undesired, it becomes necessary to use a feedback controlled mosfet with a voltage reference that is temperature stable within the desired operating range, rather than a normal zener. The source of the n-channel mosfet is connected to ground, and the drain is connected to the VDD to be protected. The output of an opamp is connected to the mosfet gate, and the mosfet drain is connected to the + input of the opamp. The temperature stable voltage reference is connected to the negative input if the opamp. Thus if VDD falls below Vref, then the gate voltage will be brought low, making the mosfet high impedance. And if VDD rises above VRef the gate voltage will increase until it sets the mosfet impedance at the exact level required to reduce VDD to match Vref.

Amusingly, a temperature stable voltage reference can itself be made with a temperature feedback controlled current source through a zener diode.