Wrote a real README

README.md

@@ -1,3 +1,65 @@
-# pd-buddy-firmware
+# PD Buddy firmware
 
-PD Buddy firmware
+This is the firmware for the PD Buddy project.  Currently, this specifically
+means the PD Buddy Sink.  The firmware is currently under heavy development,
+but is partially functional.
+
+## Prerequisites
+
+To compile the firmware, you must first install the [GNU ARM Embedded
+Toolchain](https://launchpad.net/gcc-arm-embedded).  Details of its
+installation is beyond the scope of this README.  Once the toolchain is
+installed, clone this repository with:
+
+    $ git clone --recursive http://git.clayhobbs.com/clay/pd-buddy-firmware.git
+
+This will give you a complete copy of the repository, including the ChibiOS
+submodule.
+
+You will also need to install some program to flash the firmware.  The simplest
+option is [dfu-util](http://dfu-util.sourceforge.net/), as it requires no extra
+hardware.  If you prefer to use SWD, you could also use
+[stlink](https://github.com/texane/stlink) or [OpenOCD](http://openocd.org/).
+
+## Compiling
+
+With all the dependencies installed, the firmware can be compiled as follows:
+
+    $ cd pd-buddy-firmware
+    $ make
+
+This compiles the firmware to `build/pd-buddy-firmware.{bin,elf}`.
+
+## Flashing
+
+The firmware can be flashed in any number of ways, including but not limited to
+the following:
+
+### dfu-util
+
+Set the boot mode switch on the PD Buddy Sink to DFU mode and plug it into your
+computer.  Flash the firmware with:
+
+    $ dfu-util -a 0 -s 0x08000000:leave -D build/pd-buddy-firmware.bin
+
+Don't forget to set the switch back to normal mode after unplugging the device.
+
+### stlink
+
+If you have an ST-LINK/V2, you can use it to flash the firmware via SWD as
+follows:
+
+    $ st-flash write build/pd-buddy-firmware.bin 0x8000000
+
+### OpenOCD
+
+OpenOCD can also be used to flash the firmware.  For example:
+
+    $ openocd -f interface/stlink-v2.cfg -f target/stm32f0x.cfg -c "program build/pd-buddy-firmware.bin verify reset exit"
+
+## Usage
+
+Currently, there isn't much to say here.  Plug it into your power supply, and
+the PD Buddy Sink will negotiate 2.25 A at 20 V.  This can be configured by
+editing `dpm_desired_v` and `dpm_desired_i` in `src/device_policy_manager.c`,
+then recompiling and reflashing.

src/device_policy_manager.c

@@ -28,8 +28,8 @@
 
 /* The voltage and current we want */
 /* XXX In the future, these won't be *quite* so convenient to access */
-static uint16_t dpm_desired_v = 400; /* 20 V */
-static uint16_t dpm_desired_i = 225; /* 2.25 A */
+static uint16_t dpm_desired_v = 400; /* 0.05 V increments */
+static uint16_t dpm_desired_i = 225; /* 0.01 A increments */
 
 /* Whether or not the power supply is unconstrained */
 static uint8_t dpm_unconstrained_power;