Improve Readme and crate documentation

Show `SerialPort` example on all architectures, but only try to compile it on `x86_64`.

Author: phil-opp

README.md

@@ -2,11 +2,16 @@
 
 [![Build Status](https://github.com/rust-osdev/uart_16550/workflows/Build/badge.svg)](https://github.com/rust-osdev/uart_16550/actions?query=workflow%3ABuild) [![Docs.rs Badge](https://docs.rs/uart_16550/badge.svg)](https://docs.rs/uart_16550/)
 
-Minimal support for uart_16550 serial and memory mapped I/O.
+Minimal support for [serial communication](https://en.wikipedia.org/wiki/Asynchronous_serial_communication) through [UART](https://en.wikipedia.org/wiki/Universal_asynchronous_receiver-transmitter) devices, which are compatible to the [16550 UART](https://en.wikipedia.org/wiki/16550_UART). This crate supports port-mapped and memory mapped UARTS.
 
 ## Usage
 
-### With usual serial port
+Depending on the system architecture, the UART can be either accessed through [port-mapped I/O](https://wiki.osdev.org/Port_IO) or [memory-mapped I/O](https://en.wikipedia.org/wiki/Memory-mapped_I/O).
+
+### With port-mappd I/O
+
+The UART is accessed through port-mapped I/O on architectures such as `x86_64`. On these architectures, the [`SerialPort`](https://docs.rs/uart_16550/~0.2/uart_16550/struct.SerialPort.html) type can be used:
+
 
 ```rust
 use uart_16550::SerialPort;
@@ -25,6 +30,8 @@ let data = serial_port.receive();
 
 ### With memory mapped serial port
 
+Most other architectures, such as [RISC-V](https://en.wikipedia.org/wiki/RISC-V), use memory-mapped I/O for accessing the UARTs. On these architectures, the [`MmioSerialPort`](https://docs.rs/uart_16550/~0.2/uart_16550/struct.MmioSerialPort.html) type can be used:
+
 ```rust
 use uart_16550::MmioSerialPort;
 
@@ -40,10 +47,6 @@ serial_port.send(42);
 let data = serial_port.receive();
 ```
 
-## License
-
-Licensed under the MIT license ([LICENSE](LICENSE) or <http://opensource.org/licenses/MIT>).
-
 ## Crate Feature Flags
 
 * `nightly`: This is the default.
@@ -53,3 +56,7 @@ Licensed under the MIT license ([LICENSE](LICENSE) or <http://opensource.org/lic
 
 This needs to have the [compile-time requirements](https://github.com/alexcrichton/cc-rs#compile-time-requirements) of the `cc` crate installed on your system.
 It was currently only tested on Linux and MacOS.
+
+## License
+
+Licensed under the MIT license ([LICENSE](LICENSE) or <http://opensource.org/licenses/MIT>).

src/lib.rs

@@ -1,29 +1,47 @@
-//! Minimal support for uart_16550 serial I/O.
+//! Minimal support for
+//! [serial communication](https://en.wikipedia.org/wiki/Asynchronous_serial_communication)
+//! through [UART](https://en.wikipedia.org/wiki/Universal_asynchronous_receiver-transmitter)
+//! devices, which are compatible to the [16550 UART](https://en.wikipedia.org/wiki/16550_UART).
 //!
-//! # Usage
-
-#![cfg_attr(
-    target_arch = "x86_64",
-    doc = "
-## With usual serial port
-```no_run
-use uart_16550::SerialPort;
-
-const SERIAL_IO_PORT: u16 = 0x3F8;
-
-let mut serial_port = unsafe { SerialPort::new(SERIAL_IO_PORT) };
-serial_port.init();
-
-// Now the serial port is ready to be used. To send a byte:
-serial_port.send(42);
-
-// To receive a byte:
-let data = serial_port.receive();
-```
-"
-)]
-
-//! ## With memory mapped serial port
+//! This crate supports port-mapped and memory mapped UARTS.
+//!
+//! ## Usage
+//!
+//! Depending on the system architecture, the UART can be either accessed through
+//! [port-mapped I/O](https://wiki.osdev.org/Port_IO) or
+//! [memory-mapped I/O](https://en.wikipedia.org/wiki/Memory-mapped_I/O).
+//!
+//! ### With port-mappd I/O
+//!
+//! The UART is accessed through port-mapped I/O on architectures such as `x86_64`.
+//! On these architectures, the  [`SerialPort`] type can be used:
+//!
+//!
+//! ```no_run
+//! # #[cfg(target_arch = "x86_64")]
+//! # fn main() {
+//! use uart_16550::SerialPort;
+//!
+//! const SERIAL_IO_PORT: u16 = 0x3F8;
+//!
+//! let mut serial_port = unsafe { SerialPort::new(SERIAL_IO_PORT) };
+//! serial_port.init();
+//!
+//! // Now the serial port is ready to be used. To send a byte:
+//! serial_port.send(42);
+//!
+//! // To receive a byte:
+//! let data = serial_port.receive();
+//! # }
+//! # #[cfg(not(target_arch = "x86_64"))]
+//! # fn main() {}
+//! ```
+//!
+//! ### With memory mapped serial port
+//!
+//! Most other architectures, such as [RISC-V](https://en.wikipedia.org/wiki/RISC-V), use
+//! memory-mapped I/O for accessing the UARTs. On these architectures, the [`MmioSerialPort`]
+//! type can be used:
 //!
 //! ```no_run
 //! use uart_16550::MmioSerialPort;