UBootEnv

This library lets you read and write U-Boot environment blocks from Elixir. U-Boot environment blocks are simple key-value stores used by the U-Boot bootloader and applications that need to communicate with it. Nerves uses U-Boot environment blocks to store settings related to the device and running firmware. Nerves uses the format even for boards (like the Raspberry Pis) that don't use the U-Boot bootloader.

This library has the following features:

Create, read, and write to U-Boot environment blocks in pure Elixir with OTP 21 and later
Load environment block configurations from /etc/fw_env.config
Redundant and non-redundant environment block support

This library does not support U-Boot environment blocks stored in raw NAND Flash or big-endian blocks.

Installation

Install by adding uboot_env to your list of dependencies in mix.exs:

def deps do
  [
    {:uboot_env, "~> 1.0"}
  ]
end

Using

Here's an example of reading the environment:

iex> UBootEnv.read()
{:ok,
 %{
   "fdt_addr" => "0x83000000",
   "stdout" => "serial",
   ...
 }
}

To change the environment, update the map returned by UBootEnv.read/0 and call UBootEnv.write/1. If you're used to using fw_setenv, note that UBootEnv.write/1 writes the map that you give it whereas fw_setenv merges the key value pairs with the current environment.

iex> {:ok kv} = UBootEnv.read()
iex> new_kv = Map.put(kv, "hello", "world")
iex> UBootEnv.write(new_kv)
:ok

UBootEnv.read/0 and UBootEnv.write/1 do not perform any locking of the data they write. If you have multiple processes updating the U-Boot environment block, you'll have to synchronize access to it.

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