docs/samd: Add documentation for the samd port.

Includes a general overview, a quickref, pinout tables, and the beginnings
of a tutorial.

Author: robert-hh

docs/index.rst

@@ -17,3 +17,4 @@ MicroPython documentation and references
     unix/quickref.rst
     zephyr/quickref.rst
     renesas-ra/quickref.rst
+    samd/quickref.rst

docs/samd/general.rst

@@ -0,0 +1,88 @@
+.. _samd_general:
+
+General information about the SAMD port
+=======================================
+
+The SAMD21/SAMD51 MCU family is a high performance family of devices made by MicroChip.
+The SAMD21 devices are based on an ARM M0+ core, the SAMD51 device on ARM Cortex M4 core.
+They provide many on-chip I/O units for building small to medium sized devices.
+
+Multitude of boards
+-------------------
+
+There is a multitude of modules and boards from different sources which carry
+an SAMD21/SAMD51 chip.  MicroPython aims to provide a generic port which runs on
+as many boards/modules as possible, but there may be limitations.  The
+Adafruit ItsyBitsy M0 Express, Adafruit Feather M4 Express and the Adafruit ItsyBitsy M4 Express
+development boards are taken as reference for the port (for example, testing is performed on them).
+For any board you are using please make sure you have a data sheet, schematics
+and other reference materials so you can look up any board-specific functions.
+
+The following boards are at the moment supported by the port:
+
+- ADAFRUIT FEATHER M0 EXPRESS
+- ADAFRUIT FEATHER M4 EXPRESS
+- ADAFRUIT ITSYBITSY M0 EXPRESS
+- ADAFRUIT ITSYBITSY M4 EXPRESS
+- ADAFRUIT TRINKET M0
+- MINISAM M4
+- SAMD21 XPLAINED PRO
+- SEEED WIO TERMINAL
+- SEEED XIAO
+
+To make a generic SAMD port and support as many boards as possible the
+following design and implementation decision were made:
+
+* GPIO pin numbering is based on the board numbering.
+  Please have the manual/pin diagram of your board at hand
+  to find correspondence between your board pins and actual SAMD21/SAMD51 pins.
+  For the boards listed above, the relation between the board pin number and
+  the GPIO number can be found at :ref:`samd_pinout`.
+* The pins that can be used by MicroPython are limited to those listed
+  in the board definition files.
+
+Technical specifications and SoC data sheets
+--------------------------------------------
+
+The data sheets and other reference material for SAMD21/SAMD51 chip are available
+from the vendor site: https://www.microchip.com/en-us/products/microcontrollers-and-microprocessors/32-bit-mcus/sam-32-bit-mcus
+They are the primary reference for the chip technical specifications, capabilities,
+operating modes, internal functioning, etc.
+
+For your convenience, a few technical specifications are provided below:
+
+SAMD21:
+
+* Architecture: ARM Cortex M0+
+* CPU frequency: up to 48MHz
+* Total RAM available: up to 32 kB (see table)
+* Internal FlashROM: up to 256 kB
+  Some boards provide additional external SPI flash.
+* GPIO: up to 52 (GPIOs are multiplexed with other functions, including
+  external FlashROM, UART, etc.)
+* UART: up to 6 serial devices, which can used for UART, SPI or I2C.
+* I2S: 1 I2S interfaces
+* ADC: One 12-bit SAR ADC converter with 16 channels.
+* Programming: using BootROM bootloader from USB.
+
+SAMD51:
+
+* Architecture: ARM Cortex M4
+* CPU frequency: up to 120MHz
+* Total RAM available: up to 256 kB
+* Internal FlashROM: up to 1 MB
+  Some boards provide additional external SPI flash.
+* GPIO: up to 99 (GPIOs are multiplexed with other functions, including
+  external FlashROM, UART, etc.)
+* UART: up to 8 serial devices, which can used for UART, SPI or I2C.
+* I2S: 1 I2S interfaces
+* ADC: Dual 12-bit SAR ADC converter with 16 channels.
+* Programming: using BootROM bootloader from USB.
+
+
+For more information see the excellent SAMD21/SAMD51 data sheets or reference manuals.
+
+At the moment, the SAM21 port of MicroPython requires 256kB flash, of which 64kB is used
+for a small file system. The SAM51 port requires 512 kB of flash, of which all flash beyond
+384kB is used for a file system. Some boards have additional flash memory, which can be used
+as additional file space.