Category: Android

DigiSpark ATTiny85 Revisited

Finally got the thing to program. I went and bought some of the semi-bare USB units. All told, I think you can get this device in 4 different forms (or more).

  1. Bare chip. Should be easy to program as long as you have the right voltages and drivers.
  2. Bare chip-on-a-board. Same as bare chip but it’s on its own breakout board with a little support circuitry
  3. USB with bare connection. Like some cheap thumb drives, the card edge plugs straight into a USB port.
  4. USB with mini/micro connection. Basically #3 except you connect via a standard USB cable.

It was case #4 I was having so much trouble with, so I bought some #3s figuring that they might match available docs better.

They did, and it gave me a clue as to why the #4 boards didn’t program.

The ATTiny85 is programmed via a slightly non-standard Arduino service called Micronucleus. Micronucleus goes straight to the USB hardware. And by straight, I mean that it doesn’t even expect the device in question to be a named OS device. In Linux, that means nothing appears under /dev when you plug the ATTiny USB device in.

I installed the udev rules given for Ubuntu into my Fedora system. I haven’t dissected them, but I’m pretty sure that that’s what they’re for – capturing the hotplug of the ATTiny device and keeping it from mapping to /dev. The access rules given were 0666 and by reading carefully over available documentation I learned that often running the Micronucleus utility as root would clear up the error I was getting: “Assertion `res >= 4′ failed.”

666 doesn’t allow “execute” rights, so maybe on Fedora that’s a problem. The other alternative would be an selinux problem, but my audit logs don’t seem to indicate that.

So, by running the entire IDE as root (pending further discovery), I can now upload to the DigiSpark. Once I had the case #3 units, the case #4 units worked as well. Apparently they’re essentially identical except for their connection hardware.

I’m now poised to enjoy this inexpensive but useful little device. All is not forgiven, which is why I leave my original complaints posted. But at least I no longer have a box of useless parts.

 

 

The Dark Side of the Nook

I knew that people were unhappy with the Nook Tablet because it reserved a lot of memory for itself, but I hadn’t realized how far the rot has truly run.

One of the reasons why this unit appealed to me was that I expected it to continue the open-ness of the Nook Color, its predecessor. Sadly, this is not so. The only way to root a Nook Tablet is to wipe it back to factory settings. While on the whole, I like the tablet’s native OS, the B&N app store is pretty thin as far as some of my favorite Android apps go, and I’m displeased that I have been blocked from doing anything about that.

More serious, however, is what they’ve done to the books themselves. Side-loaded books are second-class citizens. B&N purchases are completely hidden from side-loading access. And therefore, the only backup mechanism is to re-retrieve them from the B&N servers.

When I buy a book, I expect that I’ve bought the book. An attractive feature of the Nook was that in case B&N ever bail from the business or a superior reader came along, I could decrypt and read my books anytime I wanted to on other platforms and not have them simply evaporate as some of the music services did. With the Nook tablet, this isn’t true anymore.

If I wanted a platform where other people controlled everything I did, I’d get an iPad.

Android – Projection Maps explained

Android comes with the SQLite database. Although it’s a lighweight DBMS, its authors are sufficiently proud of it that instead of listing what features it has, they prefer to list what features it doesn’t!

In addition to the SQL support we all know and love, Android includes some SQLite features that aren’t really well explained. First and foremost of which is the SQL Query Builder. Although nominally it’s a way to construct SQL without “knowing SQL”, I suspect its more important feature is that it makes it easier to construct SQL from context URIs.

One item, however, which has proven to be really frustrating is the Projection Map. Actually, I’m not even where they pulled the term “projection” from, but Projection Maps have been a real poser for me. I finally broke down and looked at the SQLQueryBuilder source code. A reminder: a ProjectionMap is a Map<String, String>.

Here’s what I found.

If you read the JavaDocs, you’d get the impression that Projection Maps effectively provide a “poor man’s database view” where you can simplify selection request items (projections). In actuality, it’s not so straightforward. Or maybe it is, but the explanation isn’t. It doesn’t help that the literature is rife with projection maps whose sole purpose in life seems to be to convert something to itself: “table1._id” => “table1._id” and so forth.

First of all, you don’t even need a projection map unless you want one. Just don’t set it. If you take that approach, the projection names are processed “as is”, exactly as passed in via the projection array.

Secondly, even the projection array is optional. If you pass null, it generates a “SELECT *” operation. In general, that’s not recommended in SQL, because of the breakage that can occur if columns are added/removed, or re-ordered, but that option is still available if you need it.

Thirdly, the projection map, if supplied applies only to the selection list! In other words, you could map “store_name” => “bookstore.storename”, and it would result in “select bookstore.storename …”, but if you supplied “store_name” in the “order by” query builder parameter or one of the other qualified parameters, you can potentially end up with bad SQL.

Fourth, the projection map can be overruled. If the key part of a projection entry contains an “as” clause, the value part is ignored and the key part is inserted into the resulting SQL. For example “parrot as polly” => “cracker” will generate “SELECT parrot as polly …” and no crackers. The “as” can be either all upper-case or all lower-case (not mixed case) and must have at least one space before and after the word “as”.

Fifth, if you provide a projection map and no projection array, the projection map’s value entries are used to generate the select item list and the projection map’s keys are ignored. In other words, “parrot as polly” => “cracker” will result in “SELECT cracker, but only if no projection array (zero elements or null) is supplied. It’s not a safe thing, however to make a map like “parrot as polly” => “cracker as graham”.  At the moment, that would result in “SELECT cracker as graham”, but only if no select array was supplied. But that’s probably an artifact, not an intended behavior.

Sixth, and finally, If you do provide both a projection map and a projection array, each and every element in the array must appear as a key in the map! Any omissions will cause the SQLQueryBuilder to throw an IllegalArgumentException (Invalid column) when it attempts to build the SQL. That one’s mentioned in the JavaDocs, by the way.

Now you know. And so do I.

Android ListViews with Checkboxes

Android has a very useful way of organizing lists: the ListView. However, it doesn’t seem to work right when you include a checkbox in the list!

Actually, it turns out that it works exactly right, but only if you understand what “right” actually is.

The normal behavior of a ListView item is that you can highlight it and click it and the whole item line participates. Not so when the line includes a checkbox. Why? http://www.mail-archive.com/android-developers@googlegroups.com/msg11390.html

Which says, in brief: If a Listview contains an item that can receive focus, that item receives events instead of the listview.

It turns out that that is literally true. Set the “focusable” attribute on the CheckBox to false and the magic returns: http://stackoverflow.com/questions/1121192/android-custom-listview-unable-to-click-on-items . Don’t forget to manually set the “checked” attribute when you handle the list item click!

Here’s an interesting bit of code: http://www.anddev.org/checkbox_text_list___extension_of_iconified_text_tutorial-t771.html