merge libmaple docs ("leaflabs-docs") into ./docs

In the past, libample documentation was forked out of this repository
because the documentation had increased in scope. For the librambutan,
and the rambutan project in general, we will try to keep documentation
closer to the source code, so the librambutan-specific documentation
should live here. Other sections of leaflabs-docs will be culled in a
following commit.

This merge attempts to maintain history by using a subtree strategy.
Followed directions at:

    http://nuclearsquid.com/writings/subtree-merging-and-you/

Full history for files should be accessible using the "--follow" flag to
git log, eg:

    git log --follow docs/source/adc.rst

It should be possible to pull patches from leaflabs-docs with:

    git pull -s subtree leaflabs-docs master

... at least until the docs in this repository diverge significantly.

1 files changed, 466 insertions, 0 deletions

diff --git a/docs/source/hardware/maple-ret6.rst b/docs/source/hardware/maple-ret6.rst
new file mode 100644
index 0000000..3d2d037
--- /dev/null
+++ b/docs/source/hardware/maple-ret6.rst
@@ -0,0 +1,466 @@
+.. highlight:: sh
+
+.. _maple-ret6:
+
+Maple RET6 Edition
+==================
+
+This page is a general resource for information specific to the Maple
+RET6 Edition.  The Maple RET6 Edition is a "beta" board released as a
+simple way to get a more powerful chip (the STM32F103\ **RET6**, hence
+the name) than the one on the base Maple (the STM32F103\ **RBT6**) in
+the hands of Maple developers.
+
+.. contents:: Contents
+   :local:
+
+.. TODO [dma.rst] Ref to source/dma.rst in sequel instead of libmaple-dma
+.. TODO [dac.rst] Ref to source/dac.rst in sequel instead of libmaple-dac
+.. TODO [nvic.rst] Ref to source/nvic.rst in sequel
+
+Technical Specifications
+------------------------
+
+* MCU: :ref:`STM32F103RET6 <maple-ret6-stdocs>`, a 32-bit ARM Cortex
+  M3 microprocessor
+* Clock Speed: **72 MHz**
+* **512 KB Flash** and **64 KB SRAM**
+* 43 :ref:`digital I/O pins (GPIOs) <gpio>`
+* 18 :ref:`PWM <pwm>` pins at 16 bit resolution
+* 15 :ref:`analog input (ADC) <adc>` pins at 12 bit resolution
+* Built-in, 2 channel **DAC** at 12 bit resolution (:ref:`libmaple-dac`).
+* 2 :ref:`SPI <spi>` peripherals with **I2S** support
+* 2 :ref:`I2C <i2c>` peripherals
+* 12 Channels of Direct Memory Access (**DMA**) (:ref:`libmaple-dma`)
+  with 2 DMA controllers
+* 3 :ref:`USART (serial port) <usart>` peripherals
+* 2 advanced, 4 general-purpose, and 2 basic :ref:`timers <timers>`
+* Dedicated :ref:`USB <usb>` port for programming and communications
+* :ref:`JTAG <jtag>`
+* Nested Vectored Interrupt Controller (NVIC) (including
+  :ref:`external interrupt <lang-attachinterrupt>` on GPIOs)
+* Supplies up to 500 mA at 3.3 V, with :ref:`separate 250 mA digital
+  and analog regulators <maple-ret6-adc-bank>` for low-noise analog
+  performance
+* :ref:`Open-source, four layer design <maple-ret6-hardware>`
+* Support for low power, sleep, and standby modes (<500 μA)
+* Operating Voltage: 3.3 V
+* Input Voltage (recommended): 4 V — 12 V
+* Dimensions are 2.05″ × 2.1″
+
+.. _maple-ret6-powering:
+
+Powering the Maple RET6 Edition
+-------------------------------
+
+The Maple RET6 Edition is powered in the :ref:`same way as the
+standard Maple <maple-powering>`.
+
+.. warning:: The RET6 Edition silkscreen falsely indicates that the
+   barrel jack accepts up to 18 V.  We recommend a barrel jack input
+   voltage **no greater than 12V**, and potentially even lower
+   depending upon the current draw requirements of the
+   application. The same goes for powering off LiPo batteries.
+
+   Please see :ref:`Power Regulation on the Maple
+   <maple-power-regulation>` for more information.
+
+.. _maple-ret6power-regulation:
+
+Power Regulation on the Maple RET6
+----------------------------------
+
+Power regulation on the Maple RET6 works in the :ref:`same way as the
+standard Maple <maple-power-regulation>`.
+
+Using the Built-in Battery Charger
+----------------------------------
+
+The RET6 Edition has a built-in LiPo battery charger.  In order to use
+it, put a jumper across the CHRG header on the power selection header
+and across the USB, or EXT selectors, depending on whether you're
+charging the battery via USB cable or barrel jack connector.  The LED
+labeled CHRG will light up while the battery is being charged.  When
+the battery is finished charging, the LED labeled DONE will light up.
+
+.. _maple-ret6-gpios:
+
+GPIO Information
+----------------
+
+The RET6 Edition features 38 ready-to-use general purpose input/output
+(see :ref:`gpio`) pins for digital input/output, numbered ``D0``
+through ``D37``.  These numbers correspond to the numeric values next
+to each header on the Maple silkscreen.
+
+.. _maple-ret6-but:
+
+Pin ``D38`` is the board's :ref:`button pin <lang-board-values-but>`.
+It is thus mainly useful as an :ref:`input <lang-pin-levels>`.  The
+pin will :ref:`read <lang-digitalread>` ``HIGH`` when the :ref:`button
+is pressed <lang-isbuttonpressed>`.
+
+More GPIOs (numbered ``D39``\ --``D42`` on the back of the RET6
+Edition's silkscreen) are available if you use the
+:ref:`lang-disabledebugports` function; see the :ref:`board-specific
+debug pin constants <lang-board-values-debug>` for more information.
+(See :ref:`this erratum <maple-ret6-nrst-pb4>` for information about
+the pin numbered ``43`` on the silkscreen).
+
+.. TODO [0.1.0] silkscreen pictures which expand abbreviations
+
+.. _maple-ret6-pin-map-master:
+
+Master Pin Map
+^^^^^^^^^^^^^^
+
+This table shows a summary of the available functionality on every
+GPIO pin, by peripheral type.  The "5 V?" column documents whether or
+not the pin is :ref:`5 volt tolerant <gpio-5v-tolerant>`.
+
+Note that this table is not exhaustive; on some pins, more peripherals
+are available than are listed here.
+
+.. csv-table::
+   :header: Pin, :ref:`GPIO <gpio>`, :ref:`ADC <adc>`, :ref:`Timer <timers>`, :ref:`I2C <i2c>`, :ref:`UART/USART <usart>`, :ref:`SPI <spi>`, 5 V?
+
+   D0,  PA3,  CH3,  2_CH4,     -,       2_RX,  -,      -
+   D1,  PA2,  CH2,  2_CH3,     -,       2_TX,  -,      -
+   D2,  PA0,  CH0,  2_CH1_ETR, -,       2_CTS, -,      -
+   D3,  PA1,  CH1,  2_CH2,     -,       2_RTS, -,      -
+   D4,  PB5,  -,    -,         1_SMBA,  -,     3_MOSI, -
+   D5,  PB6,  -,    4_CH1,     1_SCL,   -,     -,      Yes
+   D6,  PA8,  -,    1_CH1,     -,       1_CK,  -,      Yes
+   D7,  PA9,  -,    1_CH2,     -,       1_TX,  -,      Yes
+   D8,  PA10, -,    1_CH3,     -,       1_RX,  -,      Yes
+   D9,  PB7,  -,    4_CH2,     1_SDA,   -,     -,      Yes
+   D10, PA4,  CH4,  -,         -,       2_CK,  1_NSS,  -
+   D11, PA7,  CH7,  3_CH2,     -,       -,     1_MOSI, -
+   D12, PA6,  CH6,  3_CH1,     -,       -,     1_MISO, -
+   D13, PA5,  CH5,  -,         -,       -,     1_SCK,  -
+   D14, PB8,  -,    4_CH3,     -,       -,     -,      Yes
+   D15, PC0,  CH10, -,         -,       -,     -,      -
+   D16, PC1,  CH11, -,         -,       -,     -,      -
+   D17, PC2,  CH12, -,         -,       -,     -,      -
+   D18, PC3,  CH13, -,         -,       -,     -,      -
+   D19, PC4,  CH14, -,         -,       -,     -,      -
+   D20, PC5,  CH15, -,         -,       -,     -,      -
+   D21, PC13, -,    -,         -,       -,     -,      -
+   D22, PC14, -,    -,         -,       -,     -,      -
+   D23, PC15, -,    -,         -,       -,     -,      -
+   D24, PB9,  -,    4_CH4,     -,       -,     -,      Yes
+   D25, PD2,  -,    3_ETR,     -,       -,     5_RX,   Yes
+   D26, PC10, -,    -,         -,       -,     4_TX,   Yes
+   D27, PB0,  CH8,  3_CH3,     -,       -,     -,      -
+   D28, PB1,  CH9,  3_CH4,     -,       -,     -,      -
+   D29, PB10, -,    -,         2_SCL,   3_TX,  -,      Yes
+   D30, PB11, -,    -,         2_SDA,   3_RX,  -,      Yes
+   D31, PB12, -,    1_BKIN,    2_SMBA,  3_CK,  2_NSS,  Yes
+   D32, PB13, -,    1_CH1N,    -,       3_CTS, 2_SCK,  Yes
+   D33, PB14, -,    1_CH2N,    -,       3_RTS, 2_MISO, Yes
+   D34, PB15, -,    1_CH3N,    -,       -,     2_MOSI, Yes
+   D35, PC6,  -,    8_CH1,     -,       -,     -,      Yes
+   D36, PC7,  -,    8_CH2,     -,       -,     -,      Yes
+   D37, PC8,  -,    8_CH3,     -,       -,     -,      Yes
+   D38, PC9,  -,    8_CH4,     -,       -,     -,      Yes
+   D39, PA13, -,    -,         -,       -,     -,      Yes
+   D40, PA14, -,    -,         -,       -,     -,      Yes
+   D41, PA15, -,    -,         -,       -,     3_NSS,  Yes
+   D42, PB3,  -,    -,         -,       -,     3_SCK,  Yes
+
+.. _maple-ret6-gpio-port-map:
+
+GPIO Port Pin Map
+^^^^^^^^^^^^^^^^^
+
+The following table shows what pins are associated with each
+:ref:`GPIO port <gpio-ports>`.
+
+.. csv-table::
+   :header: GPIOA, GPIOB, GPIOC
+
+   PA0: D2,   PB0:  D27, PC0: D15
+   PA1: D3,   PB1:  D28, PC1: D16
+   PA2: D1,   PB2:  -,   PC2: D17
+   PA3: D0,   PB3:  D42, PC3: D18
+   PA4: D10,  PB4:  D43, PC4: D19
+   PA5: D13,  PB5:  D4,  PC5: D20
+   PA6: D12,  PB6:  D5,  PC6: D35
+   PA7: D11,  PB7:  D9,  PC7: D36
+   PA8: D6,   PB8:  D14, PC8: D37
+   PA9: D7,   PB9:  D24, PC9: D38
+   PA10: D8,  PB10: D29, PC10: D26
+   PA11: -,   PB11: D30, PC11: -
+   PA12: -,   PB12: D31, PC12: -
+   PA13: D39, PB13: D32, PC13: D21
+   PA14: D40, PB14: D33, PC14: D22
+   PA15: D41, PB15: D34, PC15: D23
+
+.. _maple-ret6-timer-map:
+
+Timer Pin Map
+^^^^^^^^^^^^^
+
+The following table shows what pins are associated with a particular
+timer's capture/compare channels.  Note that timer 5's channels share
+pins with timer 2 (e.g., timer 5 channel 1 is also available on D2,
+channel 2 on D3, etc.).
+
+.. csv-table::
+   :header: Timer, Ch. 1, Ch. 2, Ch. 3, Ch. 4
+   :delim: |
+
+   1 | D6  | D7  | D8  | -
+   2 | D2  | D3  | D1  | D0
+   3 | D12 | D11 | D27 | D28
+   4 | D5  | D9  | D14 | D24
+   8 | D35 | D36 | D37 | :ref:`D38 <maple-ret6-but>`
+
+.. _maple-ret6-exti-map:
+
+EXTI Line Pin Map
+^^^^^^^^^^^^^^^^^
+
+The following table shows which pins connect to which :ref:`EXTI lines
+<external-interrupts-exti-line>` on the Maple RET6 Edition.
+
+.. list-table::
+   :widths: 1 1
+   :header-rows: 1
+
+   * - EXTI Line
+     - Pins
+   * - EXTI0
+     - D2, D15, D27
+   * - EXTI1
+     - D3, D16, D28
+   * - EXTI2
+     - D1, D17, D25
+   * - EXTI3
+     - D0, D18, D42
+   * - EXTI4
+     - D10, D19
+   * - EXTI5
+     - D4, D13, D20
+   * - EXTI6
+     - D5, D12, D35
+   * - EXTI7
+     - D9, D11, D36
+   * - EXTI8
+     - D6, D14, D37
+   * - EXTI9
+     - D7, D24, D38
+   * - EXTI10
+     - D8, D26, D29
+   * - EXTI11
+     - D30
+   * - EXTI12
+     - D31
+   * - EXTI13
+     - D21, D32, D39
+   * - EXTI14
+     - D22, D33, D40
+   * - EXTI15
+     - D23, D34, D41
+
+.. _maple-ret6-usart-map:
+
+USART Pin Map
+^^^^^^^^^^^^^
+
+The Maple RET6 Edition has three serial ports whose pins are broken
+out to headers (also known as :ref:`USARTs <usart>`). They communicate
+using the pins given in the following table.
+
+.. csv-table::
+   :header: Serial Port, TX, RX, CK, CTS, RTS
+   :delim: |
+
+   ``Serial1`` | D7  | D8  | D6  |     |
+   ``Serial2`` | D1  | D0  | D10 | D2  | D3
+   ``Serial3`` | D29 | D30 | D31 | D32 | D33
+
+Unfortunately, :ref:`UART4 and UART5 aren't completely available
+<maple-ret6-uarts>`.
+
+.. _maple-ret6-adc-bank:
+
+Low-Noise ADC Pins
+^^^^^^^^^^^^^^^^^^
+
+The six pins at the bottom right of the board (D15—D20) generally
+offer lower-noise ADC performance than other pins on the board. If
+you’re concerned about getting good ADC readings, we recommend using
+one of these pins to take your measurements.  More details in the
+:ref:`Maple hardware documentation <maple-adc-bank>`.
+
+Board-Specific Values
+---------------------
+
+This section lists the Maple RET6 Edition's :ref:`board-specific
+values <lang-board-values>`.
+
+- ``CYCLES_PER_MICROSECOND``: 72
+- ``BOARD_BUTTON_PIN``: 38
+- ``BOARD_LED_PIN``: 13
+- ``BOARD_NR_GPIO_PINS``: 44 (however, :ref:`pin D43 is not usable
+  <maple-nrst-pb4>`)
+- ``BOARD_NR_PWM_PINS``: 18
+- ``boardPWMPins``: 0, 1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 14, 24, 27, 28,
+  35, 36, 37
+- ``BOARD_NR_ADC_PINS``: 15
+- ``boardADCPins``: 0, 1, 2, 3, 10, 11, 12, 15, 16, 17, 18, 19, 20, 27, 28
+- ``BOARD_NR_USED_PINS``: 7
+- ``boardUsedPins``: ``BOARD_LED_PIN``, ``BOARD_BUTTON_PIN``,
+  ``BOARD_JTMS_SWDIO_PIN``, ``BOARD_JTCK_SWCLK_PIN``,
+  ``BOARD_JTDI_PIN``, ``BOARD_JTDO_PIN``, ``BOARD_NJTRST_PIN``
+- ``BOARD_NR_USARTS``: 3 (unfortunately, :ref:`due to the Maple Rev 5
+  design <maple-ret6-uarts>`, UARTs 4 and 5 have pins which are not
+  broken out).
+- ``BOARD_USART1_TX_PIN``: 7
+- ``BOARD_USART1_RX_PIN``: 8
+- ``BOARD_USART2_TX_PIN``: 1
+- ``BOARD_USART2_RX_PIN``: 0
+- ``BOARD_USART3_TX_PIN``: 29
+- ``BOARD_USART3_RX_PIN``: 30
+- ``BOARD_NR_SPI``: 2 (unfortunately, :ref:`due to the Maple Rev 5
+  design <maple-ret6-nrst-pb4>`, SPI3 is unavailable).
+- ``BOARD_SPI1_NSS_PIN``: 10
+- ``BOARD_SPI1_MOSI_PIN``: 11
+- ``BOARD_SPI1_MISO_PIN``: 12
+- ``BOARD_SPI1_SCK_PIN``: 13
+- ``BOARD_SPI2_NSS_PIN``: 31
+- ``BOARD_SPI2_MOSI_PIN``: 34
+- ``BOARD_SPI2_MISO_PIN``: 33
+- ``BOARD_SPI2_SCK_PIN``: 32
+- ``BOARD_JTMS_SWDIO_PIN``: 39
+- ``BOARD_JTCK_SWCLK_PIN``: 40
+- ``BOARD_JTDI_PIN``: 41
+- ``BOARD_JTDO_PIN``: 42
+- ``BOARD_NJTRST_PIN``: :ref:`43 <maple-ret6-nrst-pb4>`
+
+.. _maple-ret6-hardware:
+
+Hardware Design Files
+---------------------
+
+The hardware schematics and board layout files are available in the
+`Maple GitHub repository <https://github.com/leaflabs/maple>`_.  Other
+than the processor used, the design files for the Maple RET6 edition
+are identical to the Maple Rev 5, which are in the ``maple-r5``
+subdirectory of the Maple repository.  A schematic for a JTAG adapter
+suitable for use with Maple is available in the ``jtagadapter``
+directory.
+
+From the GitHub repository main page, you can download the entire
+repository by clicking the "Download" button.  If you are familiar
+with `Git <http://git-scm.com/>`_, you can also clone the repository
+at the command line with ::
+
+    $ git clone git://github.com/leaflabs/maple.git
+
+.. _maple-ret6-failure-modes:
+
+Failure Modes
+-------------
+
+The following known failure modes apply to all Maple boards.  The
+failure modes aren't design errors, but are easy ways to break or
+damage your board permanently.
+
+* **High voltage on non-tolerant pins**: not all header pins are 5V
+  compatible; so e.g. connecting certain serial devices in the wrong
+  way could over-voltage the pins.  The :ref:`pin-mapping master table
+  <maple-ret6-pin-map-master>` details which pins are
+  :ref:`5V-tolerant <gpio-5v-tolerant>`.
+
+Errata
+------
+
+This section lists known issues and warnings for the Maple RET6
+Edition.  Some of these are simply due to the RET6 Edition using the
+Maple's circuit board, which was not designed to accomodate extra
+features only available on the STM32F103RET6.
+
+.. _maple-ret6-barrel-jack:
+
+* **Barrel jack power supply voltage mistake**: The acceptable voltage
+  range given next to the barrel jack on the Maple RET6 is
+  **incorrect**.  The given range is 7V — 18V.  In fact, **18V is too
+  high** and should not be supplied to your board. The original
+  voltage regulators used on the Maple were rated up to 18V.  However,
+  the voltage regulators on current Maple Revs are rated up to only
+  16V, and due to the current draw requirements of the board, operate
+  properly only up to 12V.  The recommended maximum voltage you should
+  apply is **12V**, and potentially even lower depending upon the
+  current draw requirements of the application. Please see :ref:`Power
+  Regulation on the Maple <maple-power-regulation>` for more
+  information.
+
+* **Power supply marketing mistake**: We originally sold the Maple
+  RET6 Edition advertising that it was capable of supplying up to 800
+  mA; the correct value is 500 mA.
+
+.. _maple-ret6-uarts:
+
+* **UART4, UART5 GPIOs unavailable**: Pins related to UARTs 4 and 5
+  are not broken out to headers (specifically, PC11/UART4_RX and
+  PC12/UART5_TX).  This is due to the RET6 Edition's board layout
+  being that of the Maple Rev 5, which was not designed with these
+  RET6-specific features in mind.
+
+.. _maple-ret6-dac-ch2:
+
+* **DAC channel 2 on BOARD_LED_PIN**: The Maple Rev 5 connects PA5 to
+  the board's built-in LED; this is the same GPIO bit which is
+  connected to the DAC's channel 2 output.  This is also due to the
+  RET6 Edition's board layout being that of the Maple Rev 5.  The DAC
+  output channel is still available, and (if you use the
+  :ref:`standard libmaple DAC interface <libmaple-dac>`) its output is
+  buffered by default, so this may not significantly interfere with
+  its functionality.
+
+.. _maple-ret6-nrst-pb4:
+
+* **Reset and PB4 tied together**: The RET6 Edition's reset line is
+  also connected to PB4, which is labeled on the silkscreen as pin 43.
+  Thus, attempting to use pin 43 as a GPIO can reset your board.  This
+  has other implications.  Since PB4 is also the JTAG NJTRST line,
+  this prevents the :ref:`JTAG <jtag>` "reset halt" command from
+  working properly.  Also, since PB4 is SPI3_MISO, the SPI3 peripheral
+  is not fully usable.
+
+.. _maple-ret6-sdio:
+
+* **SDIO lines not broken out**: The RET6 Edition's SDIO peripheral is
+  not usable, as some of its data lines are either not broken out or
+  used for other purposes.  This is also due to the RET6 Edition's
+  board layout being that of the Maple Rev 5.
+
+.. _maple-ret6-adc-led:
+
+* **ADC on BOARD_LED_PIN**: We originally sold the Maple RET6 Edition
+  advertising 16 analog input lines.  However, one of them (the one on
+  pin 13) is also connected to the built-in LED.  The voltage drop
+  across the LED means that the analog to digital converter on that
+  pin is not really useful.  While it is still usable, its readings
+  will be incorrect.
+
+Recommended Reading
+-------------------
+
+.. _maple-ret6-stdocs:
+
+STMicro documentation for STM32F103RE microcontroller:
+
+* `Datasheet
+  <http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00191185.pdf>`_
+  (PDF); covers STM32F103xC, STM32F103xD, STM32F103xE.
+* `Reference Manual RM0008
+  <http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/REFERENCE_MANUAL/CD00171190.pdf>`_
+  (PDF); definitive resource for peripherals on the STM32F1 line.
+* `Programming Manual PM0056
+  <http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/PROGRAMMING_MANUAL/CD00228163.pdf>`_
+  (PDF); assembly language and register reference.
+* `STM32F103RE <http://www.st.com/internet/mcu/product/164485.jsp>`_
+  overview page with links to further references.