Jim's Depository

this code is not written

I purchased a pcduino v3 for a project. I specifically selected it for its Allwinner A20 processor with its dual Cortex A7 cores and SATA interface.

The vendor image I downloaded had a linux 3.4.79+ kernel which failed to work reliably with the SATA port and would freeze the computer with no debug output randomly, say every 10 minutes or so under heavy load. As is typical with ARM SoC units, the kernel source is a bit of a mess. In this case you have to get the kernel from Allwinner’s back ported android kernel, sunxi. There is some sunxi 7 support in mainline linux 3.17. Do not be deceived, it is not enough to work. I built 3.4.103++ from sunxi, which is a bit of a trial to get configured, there are a fair number of dependencies that you will only find when the compile breaks.

The 3.4.103++ kernel is working reliably for me with SATA, though my X display has broken. I’ll look into that later.

If there is a bootable SD card in the computer, it will boot from there. If not, it will fall back to its onboard NAND. I’ve elected to not touch the NAND and use it as my recovery method. Creating a bootable SD card requires a non-obvious trick. There is boot loader code which must be at block 8 and block 20 of the card. This means you cannot use a GUID partitioned card. The GUID partition table is in blocks 2 through 33.

You will need to build the these boot loaders, a stern googling for u-boot-sunxi-with-spl.bin will find all you need to know about it.

In partition 1 you will need to copy in the uEnv.txt, script.bin, and a uImage file. The uEnv.txt tells u-boot where to find your kernel and how to load it. The uImage is your kernel.

Some other things I learned along the way:

  1. Linux no longer supports root=LABEL=MYDISK on the kernel command line. It looks like it supports partition UUIDs, but without a GUID labeled disk that isn’t going anywhere. There is a NT label fallback, but I couldn’t get it to work. I’ve had to resort to direct device names and the nondeterminism that brings in the face of a drive failure.

  2. There is no meaningful documentation for the A20 chip except for a bunch of register names.

  3. If there is a CPU temperature monitor in the A20, no one knows how to use it. There is one in the AXP209 PMU which may get exposed in /sys/ if you are clever or fortunate. (I added a heatsink and fan while fighting the system hang. It didn’t help, so CPU temperature is probably not an issue. Still, I’m leaving the heatsink on.)

  4. The power connection to the board is unfortunate. They use a micro USB for power and ask for a 2 amp power source. The warning sign here is that micro USB connectors are only spec’d for 1.8 amps. Depending which of my 6 foot USB cables I use, I either get about 4.8V at 500mA, or 4.6V at 500mA. That is an uncomfortable voltage loss. I’d really have appreciated a couple of through holes where I could solder on a real header of some sort, especially since they suggest this board is suitable for 24x7 continuous use in devices. The schematic is large and disjoint, but I don’t think there is a good spot to pick this up.

  5. You can monitor your incoming voltage and current use with:

    cat /sys/devices/platform/sunxi-i2c.0/i2c-0/0-0034/axp20-supplyer.28/power_supply/ac/voltage_now
    cat /sys/devices/platform/sunxi-i2c.0/i2c-0/0-0034/axp20-supplyer.28/power_supply/ac/current_now
  6. For an idea of computer speed, a kernel compile using both cores takes about 50 minutes of wall clock time. My Core i7, (4 cores + hyper threading) does it in under 2 minutes. If you plan to do kernel work, cross compile.

  7. You don’t need that initramfs that is in the default kernel config. If you are trying to install Debian it will even mess you up. Leave it out when you build the kernel.

  8. You can get STL files for a pcduino v3 case. It is a little tight around the micro USB power connector and accessing the microSD card is about hopeless.

  9. There are mounting holes, but be careful, there isn’t much clearance around them. It would be easy to make contact between a screw head and a component. I made tiny o-rings by slicing some insulation from #8 AWG wire to stand the screw head high enough to not touch components. Nylon screws with tiny heads would be a great idea.

I was unhappy with my options for a template system on a current project, so I have created a new one which may be useful to you.

The template language is inspired by Terrence Parr’s Enforcing Strict Model-View Separation in Template Engines in which he argues that Turing complete template languages are a mistake. Logic is best left to the model and controller, with the template engine acting as a view and simply converting from the model to the desired representation.

Having used View0 for a fair bit of source code generation, I have to agree.

View0 syntax leans toward meaningful words rather than cryptic symbols for the sake of non-programmers who might need to edit templates. There are only five directives.

You can find View0 and its manual at https://bitbucket.org/jimstudt/view0.

Being mostly a crufty old C coder at this point, I don’t use much new stuff. But I have to say the source code analysis tools are pretty nifty.

When I hit the analyzer button in Xcode to run clang’s analyzer, sometimes it finds things like this for me… (A leaked buffer in a diagnostic error for one of those “can’t probably happen” error checks. Just the kind of place I can get sloppy about memory ownership.)

I particularly like how it explains itself, that it doesn’t show off (it had to know that bgetstrn() returns allocated memory without retaining ownership, it figured that out somehow, but it doesn’t feel compelled to tell me about it), and that it has never given me a false positive in my code.

It has three false positives lurking in the Lua runtime, but they are in some pretty crazy code.


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You can use OpenCL on your Intel based linux machine, but buried in the fine print you will find that it only runs on the CPU, those 300 million transistors and 25% of your processor die area in your GPU are completely useless.

I feel a little silly for making sure my servers had HD4000 GPUs in case the day came when I needed an OpenCL boost. The day came. I’m not getting it.

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I have a need to survive ISP outages, but am not large enough to have real things like BGP and serious internet connections, so I am using a telco and a cable company with a few static IPs on each.

There are various tutorials on the internet for how to cope with this, but they seem to primarily involve using iptables MARK to stain packets and then use the iproute2 functions to route them. I dislike conjoining these two tools. I am using source routing to keep everything straight, though there is a gotcha involving SNAT that needs attention when a link goes down.


  • Support more than one ISP.
  • Use the right source IP on each link to not trip packet spoof detection.
  • Survive a link going down and back up.
  • Lots of IPv4 private address machines on the inside need to be NATed on the way out.
  • IPv6 is mandatory. Using 6rd while my ISPs recover from being blindsided by that 20 year old RFC for IPv6.
  • Some servers live outside the firewall/router, I won’t speak any more of them, but they are there.


  • Load balancing. This can be addressed with your outgoing rules, but given the disparity in quality, there is little point in using the U-verse link for outbound connections if the Charter one is up. The inbound connections will still use it.
  • A single point of failure router is fine with me.

Strategy Overview:

  • Use a VLAN switch so I don’t need a flock of switches and multiple ethernet ports on the router and “outside the firewall” boxes. 
    Not required, but when you see decimal points in my ethernet device names, those are the VLAN ids.
  • Use source routing so that all packets go out the interface that matches their source IP address.
  • Use iptables SNAT to let the local machines out. Choose their SNAT address based on the outgoing interface. Let the routing rules do the routing.
  • Use conntrack to forget cached SNAT mappings when a link goes down or comes up. This is important!

VLAN Switch, 802.11q Is Your Friend

Go read about 802.11q if you are not familiar. With this you need only one switch. You can have as many virtual LANs as you like and configure on a port by port basis which LANs appear on that port. If you have gear that doesn’t do 802.11q you can set a single VLAN to show up there and work fine without any changes to that device. You will pay more for a “smart switch” with 802.11q support, but you are going to save on the number of switches, cabling, and ethernet cards. (e.g. in January 2013 I paid $220 for a 24 port gigabit 802.11q switch.)

You will have to configure your switch. My NetGear switch is configured through a web interface apparently writing by a maniacal sociopath, but it can be made to do the job.

The Source Routing

We are going to need two auxiliary routing tables to hold rules for when we know we have a U-verse address or a Charter address. These are going to get names which means we add lines to /etc/iproute2/rt_tables, (which is just a file mapping numbers to names)…

echo "200 att" >> /etc/iproute2/rt_tables
echo "201 charter" >> /etc/iproute2/rt_tables

When an interface comes up, we are going to add an ip routing rule to force packets with a Charter source address to look in that charter routing table and go out the right interface, likewise for AT&T… (Notice the “throw” rules. Some people duplicate their main table here, but I’d never keep that in sync, so I defer to the main table instead.)

# This is what makes source routing happen
ip rule add from table att

# get a fresh start on the routing table
ip route flush table att
ip route add default via dev eth2.4 table att

# get the RFC1812 private networks out, they don't want to go out this interface
# the "throw" will make them go back to your regular routing tables.
ip route add throw table att
ip route add throw table att
ip route add throw table att

The SNAT For Our Private Addresses

Nothing new here, yet…

iptables -t nat -A POSTROUTING -o eth2.4 -s -j SNAT --to-source
iptables -t nat -A POSTROUTING -o eth2.4 -s -j SNAT --to-source
iptables -t nat -A POSTROUTING -o eth2.4 -s -j SNAT --to-source

But wait! Now we have a problem. iptables connection tracking is going to learn these SNAT rules, and for instance, if you have a ping running, it will happily keep trying the dead interface after you take one down. The fix I’m using is to clear the SNAT connection tracking information with an interface goes up or down. I use this in my /etc/network/interfaces stanzas (install conntrack first)…

# We need to make NAT'd addresses choose a new path
# e.g. ICMP echo will be stuck on a dead interface if it was using this one
up conntrack -D --src-nat
down conntrack -D --src-nat

Choosing the Best Interface for Outgoing Traffic

You will want to use a metric on your default routes in order to choose the best one. (Alternatively you can get into load balancing, but my asymmetry is too high to care about that.)

I do this by not using the gateway declaration in my iface stanzas, but just do a up command instead…

#gateway --- but we want an explicit metric, so we do it this way
up ip route add default via dev eth2.4 metric 1 || true

… that is my shunned AT&T connection. I use a metric of zero on the Charter line so traffic prefers it, but will use AT&T if Charter goes down.

Now IPv6

IPv6 gets the same treatment, except you don’t have to screw with SNAT and conntrack, unless you really want to. Also, you will need some “-6” keystrokes. It helps to remember that those routing tables for att and charter are really four tables, two for IPv4 and two for IPv6.

I’ll just show you my Charter 6rd stanza, you can work it out from there.

iface charter6rd inet6 v4tunnel

# Force 6rd gateway to be on the Charter interface
pre-up ip route add via || true

# 2nd 32bits of this is my IPv4 address 
      address 2602:0100:6023:gd32::1
      netmask 32
      tty 64
      up ip -6 rule add from 2602:100:6023:gd32::/59 table charter || true
      down ip -6 rule del from 2602:100:6023:gd32::/59 table charter || true
      up ip -6 route add default dev charter6rd table charter
      post-down ip route del via
      up   ip -6 route add 2000::/3 dev charter6rd metric 5
      down ip -6 route flush dev charter6rd

What Is Wrong With This Strategy

When one of the ISPs is broken, I need to bring down their interface, otherwise traffic will happily still try to use it. There may be automated ways to do this, but I’m a simple barbarian and given the rarity of the events, I just use a little cron job that if it can’t see some portion of the internet out a particular interface, brings that interface down for a little while. I suppose playing with the default route metrics would be nicer, but like I said, simple barbarian. (I do have a nagging suspicion that if I were smarter about the load balancing it would “just work”. But I’m not.)

These are the three recipes I copied out from my mother’s box which were copied from her mother’s box. But first, let me add some things that may be obvious to cooks, but I learned from making a bunch of these pies.

  • Butterscotch doesn’t get appreciably thicker after it leaves the double boiler. Keep at it.
  • An extra egg white or two is a good idea for the meringue so you are sure you have enough.
  • I use whole milk, because I think that may have been what “milk” meant when this was first written down.
  • It is possible to whip the meringues while stirring the double boiler, but it gets a bit tricky with a hand mixer.
  • Get a head start on the double boiling before starting the meringue whipping. The butterscotch will keep warm if it gets done first.
  • As near as I can tell, the pie crust recipe is a cruel hoax. The Pillsbury pie crust box mix from the store works much better and you won’t spend 5 minutes scraping failed pie crust from your hands.
  • When you precook the pie crusts, make sure they overlap the edge of the pan. You are going to need that flange to overlap the meringue to get a good seal or the meringue will pull away as it cooks leaving you with a meringue island on your pie. I even run the meringue a little bit past the crust so it catches.
  • As you near the end of baking, flip on the broiler and then watch it like a hawk. Do not avert your gaze from the meringue. Pull the pie out when the meringue just begins to brown.

Butterscotch Pie

1 cup brown sugar
1 cup milk
3 tbsp flour
3 tbsp butter
2 egg yolks (well beaten)
1 tsp vanillaMix flour and sugar. Add yolks, butter, and milk.
Cook in a double boiler until thick.
Add vanilla.
Put in a baked pie shell.
Cover with meringue.
Bake at 225°F (about 15-20 minutes)

Pie Meringue

Beat egg white until stiff. Allow 2 tbsp of sugar for each egg.
Add sugar slowly, beating constantly.
Flavor, allowing 1/4 tsp of vanilla for 2 egg whites.

Two Crust Pie, 9 inch

2 cups flour
1 tsp salt
3/4 cup of shortening
1/2 cup ice waterAdd ice water little by little while tossing mixture.
When it sticks together that is enough water.
Bake at 500°F for 12 minutes.

Searching for nitrile gloves on Amazon. Won’t buy these.

Amazon offer to sell me used exam


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I know better than to look at graphs in my local paper. They use them like illuminated initials or other works of the rubricator. Everyone knows it isn’t a 21st century newspaper article until you’ve rubricated.

But today I received this treat…

Clearly the reds beat the blues in the senate, their column is longer. Except the numbers say the left side has 51, so maybe the blues won. And why is there a blue hiding in the red column with the pales and the zinc chromate green party? And there are only 50 dots on the blue side, not 51.

I think I see where they were heading. The 50 and the gray line provide a clue. The gray line marks the center line, so they are trying to show a tipping point for party line voting. I have no idea why they chose a different horizontal dimension to distort the data on the Senate and Governor tables.

As far as I know there is no mechanism for governors to party line vote amongst themselves, so that middle line is meaningless.

A little dragging about in Preview fixes the quantitative visualization for them… … the voting governors issue is irreparable. I should have reordered to put the winning party fill beginning in the upper left for House and Governor, but that’s more clicking and dragging than I feel like this morning.


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One of the special priveleges of coding alone…

At the end of a two hour debugging session where somehow a nearly valid pointer was showing up in an IO call back routine in a multithreaded C program I found this comment…


… and I really don’t get to blame anyone else.

I was right though. It did need work.

AT&T woke me up at 4:42am this morning to tell me that they were going to give lists of all my phone calls, who I talk to, and which web sites I visit and when to a broad list of marketing companies so that those companies could try to sell me things.

This afternoon I went to AT&T and asked for them to disable their locks from my iPhone so I could use it while out of the country. They refused since I still had a few days left in my contract with them. I was clear that I wasn’t leaving the contract, this would cost AT&T nothing. They refused.

So let’s try to opt out of CPNI:

• Link in email, wants the account id and zip code. Does not work. Account is now locked and won’t unlock. It suggests I click on a “chat” button of which there is none on the page. (This may be because I had to change the account billing zip code to my daughter’s residence to enable her femtocell.)

• The CPNI opt out page suggests I get my account number from the email. The email does not contain my account number because they replaced most of it with “x”s.

• Find my account number on an old bill…

We’re Having Trouble Processing Your CPNI Request You can still make your request by phone. Please call a representative at 1-800-288-2020.

• Call the 800 number, navigate the voice robot to be told “This office is now closed, please call during normal business hours.” No hint what those might be.

• Try to 800 number automated system. This one worked! It took three tries to get the account number in, it doesn’t like pauses while you look for the next few digits, but it did work. Maybe. There is no apparent way to see if you are actually opted in or out.

They could have just included a working link, with a unique identifier, in the opt out notification email and saved me 20 minutes. But they also could have not woken me up early on Sunday morning with their email too. They just aren’t that kind of company.

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