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diff --git a/source/arduino-compatibility.rst b/source/arduino-compatibility.rst new file mode 100644 index 0000000..e6852a0 --- /dev/null +++ b/source/arduino-compatibility.rst @@ -0,0 +1,270 @@ +.. highlight:: cpp + +.. _arduino-compatibility: + +============================= + Maple-Arduino Compatibility +============================= + +.. contents:: Contents + :local: + +Overview +-------- + +The biggest difference between the Maple and most Arduino boards is +that the Maple uses a 32-bit ARM Cortex-M3 architecture chip, while +the Arduinos have 8-bit Atmel AVR chips. The different instruction set +means that machine code (which makes up executable binary program) is +incompatible between the two, and a different compiler (actually just +a different version of `gcc <http://gcc.gnu.org/>`_) is required. + +The compiler for the regular Arduino IDE is the popular `avr-gcc +<http://www.nongnu.org/avr-libc/>`_ package; the compiler for the +Maple version of the IDE is CodeSourcery's edition of gcc for the ARM +EABI target (:command:`arm-non-eabi-gcc`). A (preliminary) reference +on :ref:`using arm-none-eabi-gcc <arm-gcc>` is available. + +The bitwidth of the processor means that the Maple can process 32-bit +operations (like adding two 32-bit integers) in a single instruction, +while an Arduino processor would have to split up large operations +into several smaller ones. In a lot of cases 8-bit operations are +plenty (integers 0-255, single characters of text, etc.), but if +you're dealing with higher resolution data, the speed up could be +significant. + +A trade-off is that code could be larger as well; program instructions +and memory locations can be up to 32 bits each. However, removal of +extra instructions and fancy packing together of simple instructions +means that programs aren't much larger (or are even smaller). + +Header Numbering and Incompatibilities +-------------------------------------- + +.. FIXME [Maple-specific values] + +The numbering of headers is different; on the Maple each GPIO has a +unique number: 0, 1, 2, all the way up to 37 (actually, there are +:ref:`a few more <jtag>`...). On the Arduino, the analog pins are +numbered separately (A0-A5) from the digital pins (D0\ -D13). + +The incompatible hardware differences are: + +* :ref:`I2C <i2c>` **port**: on most Arduinos, the |i2c| port is Analog + Input 4 (SDA) and Analog Input 5 (SCL); on the Maple, |i2c| port 1 + is D5 (SCL) and D9 (SDA), and |i2c| port 2 is D29 (SCL) and D30 + (SDA). + + It should be possible to skywire, sacrificing signal quality (due to + increased capacitance). Alternatively, |i2c| can be bit-banged + reasonably well in software. This peripheral could potentially be + rerouted internally, but we haven't looked into it. + +* :ref:`PWM <pwm>` **on D10**: all the other standard Arduino PWM + headers have PWM functionality on the Maple (D2,D3,D6,D9,D11), but + not D10. + +* **No External Voltage Reference**: The Arduino has an AREF pin which + allows the use of an external ADC voltage reference; the Maple has + an extra GPIO pin (D14) with PWM capability in this spot, and does + not allow an external voltage reference to be configured. + +* **EEPROM**: the Maple does not have any internal EEPROM. This + functionality can be emulated with regular persistent flash memory, + or with an external EEPROM chip. + +* **ISP Programming**: the Maple does not use an ISP/ICSP bus for + debugging; it uses :ref:`JTAG <jtag>`. + + +Software Language/Library Changes +--------------------------------- + +With :ref:`a few exceptions <language-missing-features>`, the entire +Wiring/Arduino language is supported. However, there are some subtle +differences, most of which are improvements: + +* **32-bit integers**: many standard functions either expect or return + full 32-bit (4 byte) integer values instead of the regular 16-bit (2 + byte) Arduino values. + +* **64-bit doubles**: The :ref:`double <lang-double>` type is a full + double-precision floating point type on the Maple; it is a + single-precision floating point value on the Arduino. + +* :ref:`pinMode() <lang-pinmode>` **types**: any :ref:`GPIO <gpio>` + (including analog pins) can be configured into one of the following + modes with a single call to ``pinMode()``: ``OUTPUT``, + ``OUTPUT_OPEN_DRAIN``, ``INPUT_FLOATING``, ``INPUT_PULLUP``, + ``INPUT_PULLDOWN``. Additionally, the PWM pins (labeled "PWM" on the + silkscreen) can be configured in ``PWM`` and ``PWM_OPEN_DRAIN`` + modes, and the analog input pins (labeled "AIN") can be configured + in ``INPUT_ANALOG`` mode. See the :ref:`GPIO documentation <gpio>` + for more information. + +* :ref:`Serial port <lang-serial>` **syntax**: like the `Arduino Mega + <http://arduino.cc/en/Main/ArduinoBoardMega>`_, the Maple has + multiple :ref:`USART ports <lang-serial>`. By default, ``Serial`` + is not mapped to any of them. Use ``Serial1`` through ``Serial3`` + instead. + +* **16-bit** :ref:`PWM <pwm>`: Arduino boards support 8-bit PWM, which + means that calls to :ref:`analogWrite() <lang-analogwrite>` take + values between 0 (always off) and 255 (always on). The Maple + supports 16-bit PWM, so the corresponding values should be between 0 + (always off) and 65535 (always on). + +* **12-bit** :ref:`ADC <adc>`: Arduino boards support 10-bit ADC, which + means that calls to :ref:`analogRead() <lang-analogread>` will + return values between 0 and 1023. The Maple supports 12-bit ADC, so + the same call will instead return values between 0 and 4095. + +Shield and Device Compatibility +------------------------------- + +.. list-table:: + :header-rows: 1 + + * - Shield/Device + - Compatible? + - Notes + + * - Ethernet shield + - Yes! + - Tested; no library yet + + * - WiFi Shield + - Yes! + - Tested; preliminary library support + + * - MIDI shield + - Yes! + - Tested; no library yet + + * - XBee shield + - Unknown + - + + * - Bluetooth shield + - Unknown + - Some Bluetooth <-> UART boards have been tested and are known + to work. + + * - Cellular shield + - Unknown + - + +Library Porting Status +---------------------- + +The state of currently ported Arduino libraries is the +:ref:`libraries`. + +.. TODO Update as libraries are ported. + +.. list-table:: + :header-rows: 1 + + + * - Library + - Ported? + - Notes + + * - Wire + - Preliminary + - In progress; see :ref:`library reference <libraries-wire>`. + + * - LiquidCrystal + - **Yes** + - :ref:`Included since IDE 0.0.7 <libraries-liquid-crystal>` + + * - Ethernet + - Not yet + - Planned + + * - EEPROM + - (Unsupported) third-party emulation + - The Maple doesn't have EEPROM; it uses flash instead. There is + an `EEPROM emulation library + <http://akb77.com/g/mcu/maple-eeprom-emulation-library/>`_ by + `x893 <http://akb77.com/g/>`_, but we haven't tested it. + + * - Firmata + - Not yet + - Planned + + * - Matrix + - Not yet + - Planned + + * - Servo + - **Yes** + - :ref:`Included since IDE 0.0.9 <libraries-servo>` + + * - SoftwareSerial + - Not yet + - Planned + + * - Sprite + - Not yet + - Planned + + * - Stepper + - Not yet + - Planned + +Sketch and Library Porting HOWTO +-------------------------------- + +In addition to the suggestions in this section, you may find many of +the individual :ref:`language reference <language>` pages useful. As +appropriate, these have "Arduino Compatibility" sections; one good +example is the :ref:`analogWrite() <lang-analogwrite-compatibility>` +function. + +- Check the hardware and header differences above, and see if your + project or shield needs to be modified (eg, add 3.3V level + converters or reroute PWM to header D10). + +- Check for ported library functionality. We intend to port all of the + core and popular libraries (like Wire, Ethernet, and the LCD screen + driver), but this task is not yet finished. (:ref:`Patches are + welcome! <libmaple-contributing>`). + +- Check for peripheral conflicts; changing the configuration of timers + and bus speeds for a feature on one header may impact all the + features on that hardware "port". For example, changing the timer + prescaler to do long PWM pulses could impact |i2c| communications on + nearby headers. + +- Rewrite any low-level code. This could potentially be very + difficult, but hopefully you've used the Arduino libraries to + abstract away the registers and other hardware-specific + details. Your sketch probably doesn't have any low-level code; a + library which wraps a particular peripheral very well may. Some + help is available in the :ref:`arm-gcc` reference. + +- Redeclare variable sizes if necessary: generics like ``int`` will + probably work unless you depend on side-effects like rollover. + +- Check every ``pinMode()``: the Maple has more modes for GPIO + pins. For example, make sure to set analog pins to ``INPUT_ANALOG`` + before reading and PWM pins to ``PWM`` before writing. The full set + of pin modes is documented in the :ref:`lang-pinmode` reference. + +- Modify PWM writes: ``pinMode()`` must be set to ``PWM``, the + frequency of the PWM pulse configured, and the duty cycle written + with up to 16-bit resolution. + +- Modify ADC reads: :ref:`lang-analogread` takes the full pin number + (not 0-5) and returns a full 12-bit reading. The ADC pin must have + its ``pinMode()`` set to ``INPUT_ANALOG``. + +- Possibly convert all Serial-over-USB communications to use + :ref:`lang-serialusb` instead of a USART :ref:`serial port + <lang-serial>`. The Maple has a dedicated USB port which is not + connected to the USART TX/RX pins in any way. + +- Check timing: Maple clock cycles are just 13.9 nanoseconds, though + the peripheral bus speeds (which limit GPIO output) are clocked + slower. |