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diff --git a/docs/source/libmaple/overview.rst b/docs/source/libmaple/overview.rst deleted file mode 100644 index d18bfe2..0000000 --- a/docs/source/libmaple/overview.rst +++ /dev/null @@ -1,336 +0,0 @@ -.. highlight:: c - -.. _libmaple-overview: - -Overview -======== - -This page is a general overview of libmaple proper. It provides a -general perspective of the library's goals and design. Examples are -given from libmaple's sources. - -.. contents:: Contents - :local: - -Design Goals ------------- - -The central goal of the libmaple project is to provide a pleasant, -consistent set of interfaces for dealing with the various peripherals -on the STM32 line. - -Let's start with the basics. If you're interested in low-level details -on the STM32, then you're going to spend a lot of quality time wading -through `ST RM0008 -<http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/REFERENCE_MANUAL/CD00171190.pdf>`_. -That document is the single most important tool in your toolbox. It -is the authoritative documentation for the capabilities and register -interfaces of the STM32 line. - -Perhaps you haven't read it in detail, but maybe you've at least -thumbed through a few of the sections, trying to gain some -understanding of what's going on. If you've done that (and if you -haven't, just take our word for it), then you know that underneath the -covers, *everything* is controlled by messing with bits in the -seemingly endless collections of registers specific to every -peripheral. The :ref:`USARTs <usart>` have data registers; (some of -the) the :ref:`timers <timers>` have capture/compare registers, the -:ref:`GPIOs <gpio>` have output data registers, etc. - -For the most part, Wirish does everything it can to hide this truth -from you. That's because when you really just want to get your robot -to fly, your LEDs to blink, or your `FM synthesizer -<https://github.com/Ixox/preen>`_ to, well, `synthesize -<http://xhosxe.free.fr/IxoxFMSynth.mp3>`_, you probably couldn't care -less about messing with registers. - -That's fine! In fact, it's our explicit goal for Wirish to be good -enough that most people never need to know libmaple proper even -exists. We want to make programming our boards as easy as possible, -after all. But the day may come when you want to add a library for an -as-yet unsupported peripheral, or you want to do something we didn't -anticipate, or you'd like to squeeze a little more speed out of a -critical section in your program. Or maybe you're just curious! - -If anything in the above paragraph describes you, then you'll find -that you need a way to translate your knowledge of RM0008 into -software. We imagine (if you're anything like us) you want to spend -the least amount of time you possibly can doing that -translation. Ideally, once you've finished your design, you want some -way to start reading and writing code right away, without having to -bushwhack your way through a thicket of clunky APIs. - -The central abstractions we've chosen to accomplish the above goals -are *register maps* and *devices*. Register maps are just structs -which encapsulate the layout of the IO-mapped memory regions -corresponding to a peripheral's registers. Devices encapsulate a -peripheral's register map as well as any other necessary information -needed to operate on it. Peripheral support routines generally -operate on devices rather than register maps. - -Devices -------- - -At the highest level, you'll be dealing with *devices*, where a -"device" is a general term for any particular piece of hardware you -might encounter. So, for example, an analog to digital converter is a -device. So is a USART. So is a GPIO port. In this section, we'll -consider some hypothetical "xxx" device. - -The first thing you need to know is that the header file for dealing -with xxx devices is, naturally enough, called ``xxx.h``. So if you -want to interface with the :ref:`ADCs <adc>`, just ``#include -"adc.h"``. - -Inside of ``xxx.h``, there will be a declaration for a ``struct -xxx_dev`` type. This type encapsulates all of the information we keep -track of for that xxx. So, for example, in ``adc.h``, there's a -``struct adc_dev``:: - - /** ADC device type. */ - typedef struct adc_dev { - adc_reg_map *regs; /**< Register map */ - rcc_clk_id clk_id; /**< RCC clock information */ - } adc_dev; - -The ADCs aren't particularly complicated. All we keep track of for an -ADC device is a pointer to its register map (which keeps track of all -of its registers' bits; see :ref:`below <libmaple-overview-regmaps>` -for more details), and an identifying piece of information which tells -the RCC (reset and clock control) interface how to turn the ADC on and -reset its registers to their default values. - -The timers on the STM32 line are more involved than the ADCs, so a -``timer_dev`` has to keep track of a bit more information:: - - /** Timer device type */ - typedef struct timer_dev { - timer_reg_map regs; /**< Register map */ - rcc_clk_id clk_id; /**< RCC clock information */ - timer_type type; /**< Timer's type */ - voidFuncPtr handlers[]; /**< User IRQ handlers */ - } timer_dev; - -However, as you can see, both ADC and timer devices are named -according to a single scheme, and store similar information. - -``xxx.h`` will also declare pointers to the actual devices you need to -deal with, called ``XXX1``, ``XXX2``, etc. (or just ``XXX``, if -there's only one) [#fgpio]_. For instance, on the Maple's -microcontroller (the STM32F103RBT6), there are two ADCs. -Consequently, in ``adc.h``, there are declarations for dealing with -ADC devices one and two:: - - extern const adc_dev *ADC1; - extern const adc_dev *ADC2; - -In general, each device needs to be initialized before it can be used. -libmaple provides this initialization routine for each peripheral -``xxx``; its name is ``xxx_init()``. These initialization routines -turn on the clock to a device, and restore its register values to -their default settings. Here are a few examples:: - - /* From dma.h */ - void dma_init(dma_dev *dev); - - /* From gpio.h */ - void gpio_init(gpio_dev *dev); - void gpio_init_all(void); - -Note that, sometimes, there will be an additional initialization -routine for all available peripherals of a certain kind. - -Many peripherals also need additional configuration before they can be -used. These functions are usually called something along the lines of -``xxx_enable()``, and often take additional arguments which specify a -particular configuration for the peripheral. Some examples:: - - /* From usart.h */ - void usart_enable(usart_dev *dev); - - /* From i2c.h */ - void i2c_master_enable(i2c_dev *dev, uint32 flags); - -After you've initialized, and potentially enabled, your peripheral, it -is now time to begin using it. The file ``xxx.h`` contains other -convenience functions for dealing with xxx devices. For instance, -here are a few from ``adc.h``:: - - void adc_set_sample_rate(const adc_dev *dev, adc_smp_rate smp_rate); - uint32 adc_read(const adc_dev *dev, uint8 channel); - -We aim to enable libmaple's users to interact with peripherals through -devices as much as possible, rather than having to break the -abstraction and consider individual registers. However, there will -always be a need for low-level access. To allow for that, libmaple -provides *register maps* as a consistent set of names and abstractions -for dealing with registers and their bits. - -.. _libmaple-overview-regmaps: - -Register Maps -------------- - -A *register map* is just a C struct which names and provides access to -a peripheral's registers. These registers are usually mapped to -contiguous regions of memory (though at times unusable or reserved -regions exist between a peripheral's registers). Here's an example -register map, from ``dac.h`` (``__io`` is just libmaple's way of -saying ``volatile`` when referring to register values):: - - /** DAC register map. */ - typedef struct dac_reg_map { - __io uint32 CR; /**< Control register */ - __io uint32 SWTRIGR; /**< Software trigger register */ - __io uint32 DHR12R1; /**< Channel 1 12-bit right-aligned data - holding register */ - __io uint32 DHR12L1; /**< Channel 1 12-bit left-aligned data - holding register */ - __io uint32 DHR8R1; /**< Channel 1 8-bit left-aligned data - holding register */ - __io uint32 DHR12R2; /**< Channel 2 12-bit right-aligned data - holding register */ - __io uint32 DHR12L2; /**< Channel 2 12-bit left-aligned data - holding register */ - __io uint32 DHR8R2; /**< Channel 2 8-bit left-aligned data - holding register */ - __io uint32 DHR12RD; /**< Dual DAC 12-bit right-aligned data - holding register */ - __io uint32 DHR12LD; /**< Dual DAC 12-bit left-aligned data - holding register */ - __io uint32 DHR8RD; /**< Dual DAC 8-bit left-aligned data holding - register */ - __io uint32 DOR1; /**< Channel 1 data output register */ - __io uint32 DOR2; /**< Channel 2 data output register */ - } dac_reg_map; - - -There are two things to notice here. First, if RM0008 names a -register ``DAC_FOO``, then ``dac_reg_map`` has a field named ``FOO``. -So, the Channel 1 12-bit right-aligned data register (RM0008: -DAC_DHR12R1) is the ``DHR12R1`` field in a ``dac_reg_map``. Second, -if RM0008 describes a register as "Foo bar register", the -documentation for the corresponding field has the same description. -This consistency makes it easy to search for a particular register, -and, if you see one used in a source file, to feel sure about what's -going on just based on its name. - -So let's say you've included ``xxx.h``, and you want to mess with some -particular register. What's the name of the ``xxx_reg_map`` variable -you want? That depends on if there's more than one xxx or not. If -there's only one xxx, then libmaple guarantees there will be a -``#define`` that looks like like this:: - - #define XXX_BASE ((struct xxx_reg_map*)0xDEADBEEF) - -That is, you're guaranteed there will be a pointer to the (only) -``xxx_reg_map`` you want, and it will be called -``XXX_BASE``. (``0xDEADBEEF`` is the register map's *base address*, or -the fixed location in memory where the register map begins). Here's a -concrete example from ``dac.h``:: - - #define DAC_BASE ((struct dac_reg_map*)0x40007400) - -How can you use these? This is perhaps best explained by example. - -* In order to write 2048 to the channel 1 12-bit left-aligned data - holding register (RM0008: DAC_DHR12L1), you could write:: - - DAC_BASE->DHR12L1 = 2048; - -* In order to read the DAC control register, you could write:: - - uint32 cr = DAC_BASE->CR; - -The microcontroller takes care of converting reads and writes from a -register's IO-mapped memory regions into reads and writes to the -corresponding hardware registers. - -That covers the case where there's a single xxx peripheral. If -there's more than one (say, if there are *n*), then ``xxx.h`` provides -the following:: - - #define XXX1_BASE ((struct xxx_reg_map*)0xDEADBEEF) - #define XXX2_BASE ((struct xxx_reg_map*)0xF00DF00D) - ... - #define XXXn_BASE ((struct xxx_reg_map*)0x13AF1AB5) - -Here are some examples from ``adc.h``:: - - #define ADC1_BASE ((struct adc_reg_map*)0x40012400) - #define ADC2_BASE ((struct adc_reg_map*)0x40012800) - -In order to read from the ADC1's regular data register (where the -results of ADC conversion are stored), you might write:: - - uint32 converted_result = ADC1_BASE->DR; - -Register Bit Definitions ------------------------- - -In ``xxx.h``, there will also be a variety of #defines for dealing -with interesting bits in the xxx registers, called *register bit -definitions*. These are named according to the scheme -``XXX_REG_FIELD``, where "``REG``" refers to the register, and -"``FIELD``" refers to the bit or bits in ``REG`` that are special. - -.. TODO image of the bit layout of a DMA_CCR register - -Again, this is probably best explained by example. Each Direct Memory -Access (DMA) controller's register map has a certain number of channel -configuration registers (RM0008: DMA_CCRx). In each of these channel -configuration registers, bit 14 is called the ``MEM2MEM`` bit, and -bits 13 and 12 are the priority level (``PL``) bits. Here are the -register bit definitions for those fields:: - - /* From dma.h */ - - #define DMA_CCR_MEM2MEM_BIT 14 - #define DMA_CCR_MEM2MEM BIT(DMA_CCR_MEM2MEM_BIT) - #define DMA_CCR_PL (0x3 << 12) - #define DMA_CCR_PL_LOW (0x0 << 12) - #define DMA_CCR_PL_MEDIUM (0x1 << 12) - #define DMA_CCR_PL_HIGH (0x2 << 12) - #define DMA_CCR_PL_VERY_HIGH (0x3 << 12) - -Thus, to check if the ``MEM2MEM`` bit is set in DMA controller 1's -channel configuration register 2 (RM0008: DMA_CCR2), you can write:: - - if (DMA1_BASE->CCR2 & DMA_CCR_MEM2MEM) { - /* MEM2MEM is set */ - } - -Certain register values occupy multiple bits. For example, the -priority level (PL) of a DMA channel is determined by bits 13 and 12 -of the corresponding channel configuration register. As shown above, -libmaple provides several register bit definitions for masking out the -individual PL bits and determining their meaning. For example, to -check the priority level of a DMA transfer, you can write:: - - switch (DMA1_BASE->CCR2 & DMA_CCR_PL) { - case DMA_CCR_PL_LOW: - /* handle low priority case */ - case DMA_CCR_PL_MEDIUM: - /* handle medium priority case */ - case DMA_CCR_PL_HIGH: - /* handle high priority case */ - case DMA_CCR_PL_VERY_HIGH: - /* handle very high priority case */ - } - -Of course, before doing that, you should check to make sure there's -not already a device-level function for performing the same task! - -What Next? ----------- - -After you've read this page, you can proceed to the :ref:`libmaple API -listing <libmaple-apis>`. From there, you can read documentation and -follow links to the current source code for those files on `libmaple's -GitHub page <https://github.com/leaflabs/libmaple>`_. - -.. rubric:: Footnotes - -.. [#fgpio] For consistency with RM0008, GPIO ports are given letters - instead of numbers (``GPIOA`` and ``GPIOB`` instead of - ``GPIO1`` and ``GPIO2``, etc.). |