:imagesdir: design
:toc: macro

image::logo-text-auto.svg[]

image::https://img.shields.io/discord/824493524413710336.svg?logo=discord[link=https://discord.gg/ShUWykk38X]

[NOTE]
This is in development; breaks in the API are bound to happen.

toc::[]

== What version of Zig to use

Right now we are following https://ziglang.org/download/[master], but once 0.11.0 is released, we will be switching to the latest stable version of Zig.

== Contributing

Please see the https://github.com/orgs/ZigEmbeddedGroup/projects/1/views/1[project page], it's used as a place to brainstorm and organize work in ZEG. There will be issues marked as `good first issue` or drafts for larger ideas that need scoping/breaking ground on.

== Introduction

This repo contains the infrastructure for getting started in an embedded Zig project; it "gets you to main()". Specifically, it offers:

* a single easy-to-use builder function that:
** generates your linker script
** sets up packages and startup code
* generalized interfaces for common devices, such as UART.
* device drivers for interacting with external hardware
* an uncomplicated method to define xref:interrupts[interrupts]

== Design

For MicroZig internals please see the xref:docs/design.adoc[Design Document].

== Does MicroZig support X hardware?

MicroZig is designed to cover as wide a swath of hardware as possible. The https://github.com/ZigEmbeddedGroup[Zig Embedded Group] has some repositories that contain hardware-specific code. You will find them with the `hardware-support-package` label. If you can't find your specific device, it doesn't mean that you can't run Zig on it, it's likely you're just the first! In that case, see xref:#getting-microzig-on-new-hardware[Getting MicroZig on New Hardare].

Start with an empty Zig project by running `zig init-exe`, and add the hardware support package as a submodule. We'll use `microchip-atmega` in our example:

[source,zig]
----
const std = @import("std");
const atmega = @import("deps/microchip-atmega/build.zig");

// the hardware support package should have microzig as a dependency
const microzig = @import("deps/hardware_support_package/deps/microzig/build.zig");

pub fn build(b: *std.build.Builder) !void {
    const optimize = b.standardOptimizeOption(.{});
    var exe = microzig.addEmbeddedExecutable( b, .{
        .name = "my-executable",
        .source_file = .{
            .path = "src/main.zig",
        },
        .backing = .{
            .board = atmega.boards.arduino_nano,

            // instead of a board, you can use the raw chip as well
            // .chip = atmega.chips.atmega328p,
        },
        .optimize = optimize,
    });
    exe.install();
}
----

`zig build` and now you have an executable for an Arduino Nano. In your application you can import `microzig` in order to interact with the hardware:

[source,zig]
----
const microzig = @import("microzig");

// `microzig.config`: comptime access to configuration
// `microzig.chip`: access to register definitions, generated code
// `microzig.board`: access to board information
// `microzig.hal`: access to hand-written code for interacting with the hardware
// `microzig.cpu`: access to AVR5 specific functions

pub fn main() !void {
    // your program here
}
----

== Getting MicroZig on New Hardware

If you have a board/chip that isn't defined in microzig, you can set it up yourself! You need to have:

* SVD or ATDF file defining registers
* flash and ram address and sizes

First, use https://github.com/ZigEmbeddedGroup/regz[Regz] to generate the register definitions for your chip and save them to a file. Then define the chip:

[source,zig]
----
const nrf52832 = Chip{
    .name = "nRF52832",
    .source = .{
        .path = "path/to/generated/file.zig",
    },
    .cpu = cpus.cortex_m4,
    .memory_regions = &.{
        MemoryRegion{ .offset = 0x00000000, .length = 0x80000, .kind = .flash },
        MemoryRegion{ .offset = 0x20000000, .length = 0x10000, .kind = .ram },
    },
};

const backing = .{
    .chip = nrf52832,
};
----

It's important that the chip name actually matches one of the entries under `devices` in the generated code.

=== Optional: JSON Register Schema

You can also invoke `regz` to generate a JSON representation of the hardware:

[source]
----
regz --json <path to svd/atdf>
----

This file could then be used by tooling. You can add it to a `Chip` like so:


[source,zig]
----
const nrf52832 = Chip{
    .name = "nRF52832",
    .json_register_schema = .{
        .path = "path/to.json",
    },
    // ...
};
----

== Interrupts

The currently supported architectures for interrupt vector generation are ARM and AVR. To define the Interrupt Service Routine (ISR) for a given interrupt, you create a function with the same name in an `interrupts` namespace, which is nested in a `microzig_options` namespace:

[source,zig]
----
pub const microzig_options = struct {
  pub const interrupts = struct {
      pub fn PCINT0() void {
        // interrupt handling code
      }
  };
}

pub fn main() !void {
    // my application
}
----

We're using compile-time checks along with the generated code to determine the list of interrupts. If a function is defined whose name is not in this list, you'll get a compiler error with the list of interrupts/valid names.