Andy Brodie

I wanted to have a fiddle writing code for the BBC Micro:bit in C, where I’d have access to the full potential of the device, most importantly the Bluetooth functionality.

Creating your own programs offline requires a non-trivial setup, regardless of your operating system.  Mostly for my own benefit, here are the URLs and simplified steps required to get up and running:

Yotta

I followed the instructions on https://lancaster-university.github.io/microbit-docs/offline-toolchains/.  What follows are my notes on what I had to do to make it work, over and above the instructions (adn what

Yotta is based on Python 2.  As I generally only code Python 3 this wasn’t a problem as there is a download of Yotta with all dependencies, available from http://yottadocs.mbed.com/#installing.

This will create some environment variables: YOTTA_INSTALL_LOCATION and YOTTA_PATH, the latter is added to the system path when you use the batch file run_yotta.bat, which is added to the desktop.

Grab SRecord from http://srecord.sourceforge.net/, this won’t get added to the path automatically, you have to do it manually.

Finally, you need GNU ARM Embedded Toolchain, from here: https://developer.arm.com/open-source/gnu-toolchain/gnu-rm/downloads.

Before you start running stuff though, you’ll need a user created on http://developer.mbed.org.  This is because when you run yotta for the first time, it’ll want you to authenticate with this site before downloading some dependencies.

Finally, you can run “Run Yotta” and follow the rest of the instructions on https://lancaster-university.github.io/microbit-docs/offline-toolchains/.

This means cloning the repo:

git clone https://github.com/lancaster-university/microbit-samples

cd microbit-samples

then run:

yt target bbc-microbit-classic-gcc

and

yt build

And finally, copy the compiled .hex file to the shared drive on the Micro:bit:

copy build\bbc-microbit-classic-gcc\source\microbit-samples-combined.hex e:

Public Key Cryptography is a hugely important invention.  It underpins the security (specifically the confidentiality) of most online commerce transactions.  Whilst it’s a complex subject and the subject of highly intricate and complex research to make the Internet a secure place to do business, the fundamentals of public key cryptography aren’t that hard to grasp.

The presentation linked to from this entry was originally part of a separate presentation I did on Bitcoin a little while ago, however in the end it felt like two separate subjects so I split it out.

So, public key cryptography in 6 slides (well, 8 if you include the title and closing slide).  Hopefully you’ll find the information contained within informative, consumable and, of course, correct!

You can see the presentation on Slideshare.net here: http://www.slideshare.net/AndyBrodieLocima/public-key-cryptography-a-brief-overview.

Microsoft PowerPoint 2010+ and PDF versions are available here:

1. Public Key Cryptography – A brief overview (PPTX)
2. Public Key Cryptography – A brief overview (PDF)

License

Public Key Cryptography – An brief overview by Andy Brodie is licensed under a Creative Commons Attribution 4.0 International License.

When serialising data to a Comma Separated Values (CSV) file, it’s important that field values that contain reserved characters are escaped correctly.  For example, if a value contains a unescaped comma, then this value will be incorrectly interpreted as two fields instead of one.

RFC4180 offers a specification and standard for CSV files, additionally I wanted to ensure that Microsoft Excel would be happy with any output generated by my converter.

The following method and unit tests demonstrate a way to do this conversion in Java.  I’ve tried to make the code as efficient during execution as possible, so you may find that static analysis tools such as CheckStyle flag cyclomatic complexity (11) and Boolean expression complexity (5), but I consider the code simple and readable in its current form.

Method code as follows:

/**
 * Serialises and escapes any value so that it can be added to a CSV file. If the value contains a double-quote, CR, LF, comma or semi-colon, then
 * the entire value is wrapped in double-quotes. Any instances of double quotes (") are replaced with two double-quotes.
 *
 * @param value Any value that can be converted to a String using a {@link Object#toString()}.
 * @return A string suitable to be embedded in to a CSV file that will be read by RFC4180 compliant application or Microsoft Excel. If null is
 *         passed, null is returned.
 */
public static String escapeForCsv(Object value) {
	// Handle either null inputs or toString() methods that return null.
	String inputString = value == null ? null : value.toString();
	if (inputString == null) {
		return null;
	}

	// Do we need to wrap the entire value in quotes?
	boolean quotesRequired = false;

	int inputLength = inputString.length();

	// Allocate a few extra bytes so we don't need to dynamically extend in the event of a quotes being required.
	final int extraCharsForQuoting = 3;
	StringBuffer retValue = new StringBuffer(inputLength + extraCharsForQuoting);

	for (int i = 0; i < inputLength; i++) {
		char ch = inputString.charAt(i);
		retValue.append(ch);
		if ((ch == 'n') || (ch == 'r') || (ch == ',') || (ch == ';') || (ch == '"')) {
			quotesRequired = true;
			if (ch == '"') {
				retValue.append(ch);
			}
		}
	}

	// Wrap the whole value in double quotes if we've found character that needed to be escaped.
	if (quotesRequired) {
		retValue.insert(0, """);
		retValue.append('"');
	}
		return retValue.toString();
}

This code is used in xml2csv, contained within StringUtil.java. Therefore the unit tests refer to the static method within this class:

@Test
public void testEscape() {
	assertNull(StringUtil.escapeForCsv(null));
	assertNull(StringUtil.escapeForCsv(new Object() {
		@Override
		public String toString() {
			return null;
		}
	}));
	assertEquals("", StringUtil.escapeForCsv(""));
	assertEquals("a", StringUtil.escapeForCsv("a"));
	assertEquals("abc", StringUtil.escapeForCsv("abc"));
	assertEquals("""""", StringUtil.escapeForCsv("""));
	assertEquals(""""a"", StringUtil.escapeForCsv(""a"));
	assertEquals(""a""b"", StringUtil.escapeForCsv("a"b"));
	assertEquals("","", StringUtil.escapeForCsv(","));
	assertEquals("",;,;"", StringUtil.escapeForCsv(",;,;"));
	assertEquals("";"", StringUtil.escapeForCsv(";"));
	assertEquals(""n"", StringUtil.escapeForCsv("n"));
	assertEquals(""nr"", StringUtil.escapeForCsv("nr"));
	assertEquals(""n""n"", StringUtil.escapeForCsv("n"n"));
}

Any comments or feedback welcome!