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This patch adds instructions on how to enable UART on AVR DA/DB chips Signed-off-by: Kerogit <kr.git@kerogit.eu>
113 lines
4.0 KiB
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113 lines
4.0 KiB
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======================
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Microchip DA/DB family
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======================
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This is an attempt to support AVR DA/DB family of MCUs
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Supported chips
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===============
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The code was developed using AVR128DA28 MCU on a breadboard. Currently,
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all testing was done with that chip. The chips in DA family are quite
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similar, the main differences are pin count and flash size. (Pin count
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also corresponds to supported peripherals, chips with more pins have
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more instances of the same peripheral, eg. more USARTs.)
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Chips in DB family are fairly similar to DA as well,
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some peripherals are missing, some features are added.
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This means that support for other chips is fairly easy to add,
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all that is needed is to provide interrupt vector definitions
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and similar data describing the chip. All architecture code should
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otherwise be written in a way to automatically support the chip.
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Currently, ``AVR128DA64`` and ``AVR128DB64`` chips are supported
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this way (ie. definitions describing the chip are provided
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but there is no board.)
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Clock Configuration
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===================
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The chip features internal high frequency oscillator, its frequency
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can be set in the Kconfig-based configuration. Clock speed in MHz
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is then provided in CONFIG_AVRDX_HFO_CLOCK_FREQ
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System Timer
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============
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System timer is provided by RTC peripheral and takes over it. (In theory,
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the Periodic Interrupt - PIT - component of it can be still used
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but they share single clock.)
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Tickless OS mode is supported in alarm mode. Configure it
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in :menuselection:`RTOS Features --> Clocks and Timers --> Support tick-less OS`
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:menuselection:`Tickless alarm` must be set, timer mode is not supported.
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:menuselection:`System timer tick period (microseconds)` also needs to be
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changed to value of at least 300. Higher value is recommended though,
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300us is not going to be precise at all.
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Peripheral Support
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==================
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The following list indicates peripherals supported in NuttX:
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========== ================
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Peripheral Notes
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========== ================
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GPIO In board code
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UART See below
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========== ================
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GPIO
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----
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For the most part, there is no need for any specific support for GPIO
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in architecture code. For example, NuttX button input driver should only
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need functions defined in the board code to work.
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The architecture code provides means to share single interrupt vector
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if the board needs to have multiple peripherals connected to a single
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I/O port. See gpio_intr_mux.rst for details and breadxavr board
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for example usage.
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UART
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----
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UART is implemented using interrupts. The chip doesn't support DMA.
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From some initial testing done using simple echo (read/write) loop
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it seems the driver cannot handle sustained data transmission
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with baud rate higher than 57600 even with the chip running at its
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highest speed. With baud rate 57600, performance was dependent
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on read/write buffer size. With buffer size of 8 there were still
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some missed bytes.
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To be able to use standard serial driver, it is needed to enable
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the peripheral in MCU-specific configuration in
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:menuselection:`System Type --> AVR DA/DB Peripheral Selections`
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UART peripherals are enabled using
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:menuselection:`Enable serial driver for USARTn` options. When enabled,
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additional option :menuselection:`Activate USART0 alternative pinout`
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is provided. See the chip datasheet for pinout information.
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Other UART settings are then configured in driver configuration
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:menuselection:`Device Drivers --> Serial Driver Support`
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For every enabled peripheral, there is a corresponding
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:menuselection:`USARTn Configuration` section. RTS/CTS and DMA support
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must NOT be enabled here, neither of those is supported.
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Each enabled peripheral is automatically registered as ``/dev/ttySn``
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device file. File name corresponds to the peripheral related to it.
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This for example means that ``USART1`` peripheral will always
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be accessed through ``/dev/ttyS1`` regardless of what other ``USART``
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peripherals are enabled (if any.)
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Supported Boards
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================
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.. toctree::
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:glob:
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:maxdepth: 1
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boards/*/*
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