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Always obey the first rule of PI-CLUB

  • IF YOUR PI GETS HOT TO THE TOUCH UNPLUG IT

  • IF YOUR PI GETS HOT TO THE TOUCH UNPLUG IT

  • IF YOUR PI GETS HOT TO THE TOUCH UNPLUG IT

  • IF YOUR PI GETS HOT TO THE TOUCH UNPLUG IT

You likely have a short somewhere and in the worst-case can fry your laptop.

Reading before lab:

  1. Read throuh Part 0 of the lab (in the README.md) to get a big-picture background of how the r/pi (and many computer systems) control devices.

  2. After doing so, read through pages 4--7 and 91---96 of the broadcom document (../../docs/BCM2835-ARM-Peripherals.annot.pdf) to see what memory addresses to read and write to get the GPIO pins to do stuff.

    Note 1: this is a low-level hardware document. You will almost certainly be missing key bits of context and so it will seem confusing. This is normal! Just skim what you don't understand and try to pull out what you can. We will cover the necessary pieces in class.

    As discussed in Part 0 of the lab, your specific goal is to figure out how to configure GPIO pin 20 (the lower right pin sticking up from the r/pi when orientated with pins on the right) to be either an output pin (e.g., that can blink an led) or an input pin (that detects when it is receiving a voltage > 3.3v). In the former case you want to figure out how to turn the pin off and on. In the latter you want to read it if it is off or on.

    The general game here (and with most hardware) is that each pin has a set of associated memory addresses (confusingly called registers in the Broadcom document) that you have to write magic values to to configure, and then read/write magic values to do input and output on. Your fetchquest is to chase down what addresses these are for GPIO pin 20, and what values you need.

  3. Look through the gpio.h and gpio.c files in part1-blink you'll be filling this in as well as the two simple programs part1-led/blink.c and part2-touch/touch.c which will call into your code. (You won't modify these two latter files.)

Hand-in deliverables:

Note: where the broadcom document uses addresses 0x7420xxxx, you'll use 0x2020xxxx.

You can work with someone else on this:

  1. Where are put32 and get32 defined?

  2. Write out the call to put32 that will set GPIO pin 20 to be an output pin (i.e., give the address and expression used as arguments).

  3. Write out the call to put32 that will set GPIO pin 20 to be an input pin (i.e., give the address and expression used as arguments).

  4. Write out the call to get32 to determine what value is held in GPIO pin 21.