README: It's "target" rather than "arch"; add overview table

# multipass - a multi-architecture library operating system

**multipass** is a C++ Library Operating System for a few embedded

architectures.  As such, it does not provide multi-threading support or similar

conveniences.  Its objective is similar to the Arduino environment: provide a

simple framework for embedded application/driver development and evaluation

with a `main()` and optional `loop()` function and a text output channel, and

then get out of the way as much as possible. It favors simplicity over

performance and proper abstraction.  Re-using components outside of multipass

should be fairly easy.

Application, architecture, and drivers are configured using `make config` (X11,

kconfig-qconf) or `make nconfig` (Terminal, kconfig-nconf). Each application

must implement `int main(void)` and do everything itself from that point on.

If the loop or wakeup features are enabled, `void loop(void)` or `void

wakeup(void)` must be implemented as well.

targets / architectures.  As such, it does not provide multi-threading support

or similar conveniences.  Its objective is similar to the Arduino environment:

provide a simple framework for embedded application/driver development and

evaluation with a `main()` and optional `loop()` function and a text output

channel, and then get out of the way as much as possible. It favors simplicity

over performance and proper abstraction.  Re-using components outside of

multipass should be fairly easy.

Application, target / architecture, and drivers are configured using `make

config` (X11, kconfig-qconf) or `make nconfig` (Terminal, kconfig-nconf). Each

application must implement `int main(void)` and do everything itself from that

point on.  If the loop or wakeup features are enabled, `void loop(void)` or

`void wakeup(void)` must be implemented as well.

## Getting Started

e.g. `./mpm arch=posix app=ledblink`

You should see some data about the compilation process, "Hello, world!", and

some numbers. As POSIX is not a standalone architecture (it builds an ELF

binary that is executed directly on Linux), you do not need a microcontroller

to run it. Terminate execution using Ctrl+C.

some numbers. As POSIX is not a standalone target (it builds an ELF binary that

is executed directly on Linux), you do not need a microcontroller to run it.

Terminate execution using Ctrl+C.

## Supported Targets

See `make config` for an up-to-date list. Unless noted otherwise, all targets

support GPIO input/output, UART output (typically using the built-in USB-TTL

chip of the respective development board), and an optional cycle counter.

The following table gives a quick overview over targets and additional

features; the remainder of this README covers details.

| Target | Clock | Non-Volatile Memory | Volatile Memory | Supported Drivers / Features |

| :--- | :---: | :--- |

| ATMega168P | 16 MHz | 512 KiB Flash + 512 B EEPROM | 1 KiB SRAM | I²C, SPI, UART, WS2812B, ADC |

| ATMega328P | 16 MHz | 32 KiB Flash + 1 KiB EEPROM | 2 KiB SRAM | I²C, SPI, UART, WS2812B, ADC |

| ATMega2560 | 16 MHz | 256 KiB Flash + 4 KiB EEPROM | 8 KiB SRAM | I²C, UART, DMX, ADC |

| MSP430FR5969 | 16 MHz | 48 (64) KiB FRAM | 2 KiB SRAM | I²C, SPI, UART, DMX, ADC |

| MSP430FR5994 | 16 MHz | 48 (256) KiB FRAM | 4 (8) KiB SRAM | I²C, SPI, UART, DMX, ADC |

| RM46L852 (Cortex-R4F) | 160 MHz | 1.25 MiB Flash | 192 KiB SRAM | |

| STM32F446RE (Cortex-M4) | 168 MHz | 512 KiB Flash | 1928 KiB SRAM | |

| STM32F746ZG (Cortex-M7) | 216 MHz | 1 MiB Flash | 320 KiB SRAM | |

| POSIX | – | – | – | I²C |

## Supported Architectures

Hardware features:

* 20bit mode (use up to 256kB FRAM for code and data)

* 20bit mode (use up to 256 KiB FRAM for code and data)

* ADC (partially)

## RM46L8 (Hercules RM46L8 Launchpad)