# AVR C Boilerplate

This is a basic boilerplate for programming AVRs in C.

The project aims to make programming Arduinos in C fun by
providing support for basic functionality like GPIO and USART,
so you can start developing without having the datasheet open
all the time.

It is intended for **ATmega328P** (the chip in Arduinos),
but can be easily adapted to other parts.

## Requirements

Before you can start coding, you need to install a few software packages:

- `avrdude` - the flash tool
- `avr-gcc` - compiler
- `avr-libc` - libc implementation for AVR
- `avr-binutils` - utils for manipulating AVR binaries
- `make` - to run the Makefile

There's a good chance you already have `make`, the rest should be in your
distribution's repos.

If you're on Arch:

```
# pacman -S base-devel avr-gcc avr-binutils avr-libc avrdude
```

If you're on Mac, you should be able to pull the stuff with *brew*.

## Getting started

The provided `main.c` is a good starting point - it contains some simple demo code.

You can compile it with `make` and flash with `make flash`.

### Before you can flash

First, check that the `avrdude` options in the file are correct for your system - especially 
the device and speed.

```ini
# AVRDUDE settings
PROG_BAUD = 57600
PROG_DEV  = /dev/ttyUSB0
PROG_TYPE = arduino

# Build the final AVRDUDE arguments
PROG_ARGS = -c $(PROG_TYPE) -p $(MCU) -b $(PROG_BAUD) -P $(PROG_DEV)
```

- Adjust `PROG_DEV` to the device your board is connected to. On Linux it's usually 
  `/dev/ttyUSB0`, but it can also be `/dev/ttyACM0` or something else. On Mac, it'll be
  `/dev/cu.xxx`. On Windows it's some `COMx`.<br>
  Linux and Mac users can use `ls /dev` to see their devices. Windows users will find
  this in their Device Manager.
- You may also adjust the baudrate (`PROG_BAUD`). Some boards need `115200`.

**TIP:** You can look what the Arduino IDE is using - it's running avrdude too.

### Adding new files

- If you *add a new C file* to the project, add an entry for it's `.o` (object file,
created by the compiler before linking) to the `OBJS` list in the Makefile.
- Similarly, if you *add a new folder with header files*, add it to `INCL_DIRS`.
- In case you need `printf` (or `printf` with floats), enable the appropriate LD_FLAGS
  in the Makefile (it's well commented). Code size will - obviously - grow quite a bit.

## Notes

- Since the Arduino Uno has a quirk where Double Speed Asynchronous Mode for USART is enabled by default, we made sure to disable this. If this mode is enabled it means that the USART baud rate is doubled, so if you were using a baud rate of `9200` in the code, you'd have to use a baud rate of 19200 in your terminal. We disabled this to keep things consistent, and because it has no real benefit. If you wish to turn this on however, you can do so by using `usart_set_2x(true);`