RP2040微控制器C SDK介绍

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"RP2040微控制器的开发文档，使用了Raspberry Pi Pico SDK，该SDK的源代码受3-Clause BSD许可证保护。文档提供了SDK的详细信息，包括技术与可靠性数据，但明确指出不提供任何明示或暗示的保修。" RP2040是树莓派公司（Raspberry Pi Ltd）推出的一款微控制器，主要用于Raspberry Pi Pico开发板。这个PDF文档详细介绍了RP2040微控制器的SDK，它是一个用于编写和运行C语言程序的软件开发工具包，旨在帮助开发者充分利用这款单片机的功能。 SDK（Software Development Kit）通常包含一组库、编译器、调试器和其他工具，使开发者能够高效地创建和优化针对特定硬件平台的应用程序。在RP2040 Pico C SDK的情况下，它可能包括针对RP2040架构定制的C编译器、头文件、示例代码和API，以帮助开发者理解和操作微控制器的各种外设，如GPIO、定时器、UART、SPI和I2C接口等。 3-Clause BSD许可证是一种开源软件许可协议，它允许用户自由地使用、复制、修改和分发源代码，但要求在进行这些操作时保留原始作者的版权信息。这意味着RP2040 Pico SDK的源代码可以被个人和商业项目使用，只要遵守许可条款。文档中还提到了技术与可靠性数据（Resources），这可能包括RP2040的数据表和其他相关规格，这些资料可能会随着时间更新。然而，树莓派公司明确声明，他们提供的这些资源“按原样”提供，不提供任何形式的明示或暗示保修。这意味着用户在使用这些数据时需要自行承担风险，如果因使用这些资源导致的任何直接、间接、偶然、特殊或后果性的损害，树莓派公司不承担责任。在实际应用中，开发者需要仔细阅读和理解RP2040的规格书，以及SDK提供的文档，以便正确地设计和实现基于RP2040的项目。通过SDK，开发者可以学习如何初始化和控制微控制器的各种功能，创建复杂的系统，同时利用SDK中的示例代码加速开发进程。 "raspberry-pi-pico-c-sdk.pdf" 是一份关于树莓派RP2040微控制器的开发文档，它提供了SDK的详细信息和源代码，使得开发者能够利用C语言进行开发，并且了解如何在实际项目中应用RP2040的特性。开发者在使用SDK时，需要注意文档中提及的法律免责声明，确保遵循开源许可协议，并对技术数据的使用负责。

30 io_rw_32 cs;

32 _REG_(PLL_PWR_OFFSET) // PLL_PWR

33 // Controls the PLL power modes

34 // 0x00000020 [5] : VCOPD (1): PLL VCO powerdown

35 // 0x00000008 [3] : POSTDIVPD (1): PLL post divider powerdown

36 // 0x00000004 [2] : DSMPD (1): PLL DSM powerdown

37 // 0x00000001 [0] : PD (1): PLL powerdown

38 io_rw_32 pwr;

40 _REG_(PLL_FBDIV_INT_OFFSET) // PLL_FBDIV_INT

41 // Feedback divisor

42 // 0x00000fff [11:0] : FBDIV_INT (0): see ctrl reg description for constraints

43 io_rw_32 fbdiv_int;

45 _REG_(PLL_PRIM_OFFSET) // PLL_PRIM

46 // Controls the PLL post dividers for the primary output

47 // 0x00070000 [18:16] : POSTDIV1 (0x7): divide by 1-7

48 // 0x00007000 [14:12] : POSTDIV2 (0x7): divide by 1-7

49 io_rw_32 prim;

50 } pll_hw_t;

52 #define pll_sys_hw ((pll_hw_t *)PLL_SYS_BASE)

53 #define pll_usb_hw ((pll_hw_t *)PLL_USB_BASE)

The structure contains the layout of the hardware registers in a block, and some defines bind that layout to the base

addresses of the instances of that peripheral in the RP2040 global address map.

Additionally, you can use one of the atomic set, clear, or xor address aliases of a piece of hardware to set, clear or toggle

respectively the specified bits in a hardware register (as opposed to having the CPU perform a read/modify/write); e.g:

hw_set_alias(pio0)->sm[1].shiftctrl = PIO_SM1_SHIFTCTRL_AUTOPULL_BITS;

Or, equivalently

hw_set_bits(&pio0->sm[1].shiftctrl, PIO_SM1_SHIFTCTRL_AUTOPULL_BITS);



NOTE

The hardware atomic set/clear/XOR IO aliases are used extensively in the SDK libraries, to avoid certain classes of

data race when two cores, or an IRQ and foreground code, are accessing registers concurrently.



NOTE

On RP2040 the atomic register aliases are a native part of the peripheral, not a CPU function, so the system DMA can

also perform atomic set/clear/XOR operation on registers.

2.3.5. Hardware Registers Library

The hardware_regs library is a complete set of include files for all RP2040 registers, autogenerated from the hardware

itself. This is all you need if you want to peek or poke a memory mapped register directly, however higher level libraries

provide more user friendly ways of achieving what you want in C/C++.

For example, here is a snippet from hardware/regs/sio.h:

Raspberry Pi Pico C/C++ SDK

2.3. SDK Library Structure 15

// Description : Single-cycle IO block

// Provides core-local and inter-core hardware for the two

// processors, with single-cycle access.

// =============================================================================

#ifndef HARDWARE_REGS_SIO_DEFINED

#define HARDWARE_REGS_SIO_DEFINED

// =============================================================================

// Register : SIO_CPUID

// Description : Processor core identifier

// Value is 0 when read from processor core 0, and 1 when read

// from processor core 1.

#define SIO_CPUID_OFFSET 0x00000000

#define SIO_CPUID_BITS 0xffffffff

#define SIO_CPUID_RESET "-"

#define SIO_CPUID_MSB 31

#define SIO_CPUID_LSB 0

#define SIO_CPUID_ACCESS "RO"

#endif

These header files are fairly heavily commented (the same information as is present in the datasheet register listings, or

the SVD files). They define the offset of every register, and the layout of the fields in those registers, as well as the

access type of the field, e.g. "RO" for read-only.



TIP

The headers in hardware_regs contain only comments and #define statements. This means they can be included from

assembly files (.S, so the C preprocessor can be used), as well as C and C++ files.

2.3.6. TinyUSB Port

In addition to the core SDK libraries, we provide a RP2040 port of TinyUSB as the standard device and host USB support

library within the SDK, and the SDK contains some build infrastructure for easily pulling this into your application.

The tinyusb_device or tinyusb_host libraries within the SDK can be included in your application dependencies in

CMakeLists.txt to add device or host support to your application respectively. Additionally, the tinyusb_board library is

available to provide the additional "board support" code often used by TinyUSB demos. See the README in Pico

Examples for more information and example code for setting up a fully functional application.



IMPORTANT

RP2040 USB hardware supports both Host and Device modes, but the two can not be used concurrently.

2.3.7. Wi-Fi on Pico W

The IP support within the Pico SDK is provided by lwIP. The lwIP raw API is always supported: the full API, including

blocking sockets, may be used under FreeRTOS or FreeRTOS SMP.

There are a number of different library building blocks used within the IP and Wi-Fi support`: pico_lwip for lwIP,

pico_cyw43_driver for the Wi-Fi chip driver, pico_async_context for accessing the non-thread-safe API (lwIP) in a consistent

way whether polling, using multiple cores, or running FreeRTOS.

Raspberry Pi Pico C/C++ SDK

2.3. SDK Library Structure 16



IMPORTANT

By default libcyw43 is licensed for non-commercial use, but users of Raspberry Pi Pico W, Pico WH, or anyone else

who builds their product around RP2040 and CYW43439, benefit from a free commercial-use licence.

These libraries can be composed individually by advanced users, but in most common cases they are rolled into a few

convenience libraries that you can add to your application’s dependencies in CMakeLists.txt:

•

pico_cyw43_arch_lwip_poll - For single-core, traditional polling-style access to lwIP on Pico W.

•

pico_cyw43_arch_threadsafe_background - For single or multicore access to lwIP on Pico W, with lwIP callbacks

handled in a low-priority interrupt, so no polling is required.

•

pico_cyw43_arch_lwip_sys_freertos - For full access to the lwIP APIs (NO_SYS=0) under FreeRTOS or FreeRTOS

SMP.

For fuller details see the pico_cyw43_arch header file. Many examples of using Wi-Fi and lwIP with the Pico SDK may be

found in the pico-examples repository.

2.3.8. Bluetooth on Pico W

The Bluetooth support within the Pico SDK is provided by BTstack. Documentation for BTstack can be found on

BlueKitchen’s website.



IMPORTANT

In addition to the standard BTstack licensing terms, a supplemental licence which covers commercial use of

BTstack with Raspberry Pi Pico W or Raspberry Pi Pico WH is provided.

See the pico-examples repository for Bluetooth examples including the examples from BTstack.

The Bluetooth support within the SDK is composed of multiple libraries:

The pico_btstack_ble library adds the support needed for Bluetooth Low Energy (BLE), and the pico_btstack_classic library

adds the support needed for Bluetooth Classic. You can link to either library individually, or to both libraries enabling the

dual-mode support provided by BTstack.

The pico_btstack_cyw43 library is required for Bluetooth use. It adds support for the Bluetooth hardware on the Pico W,

and integrates the BTstack run loop concept with the SDK’s pico_async_context library allowing for running Bluetooth

either via polling or in the background, along with multicore and/or FreeRTOS support.

The following additional libraries are optional:

•

pico_btstack_sbc_encoder - Adds Bluetooth Sub Band Coding (SBC) encoder support.

•

pico_btstack_sbc_decoder - Adds Bluetooth Sub Band Coding (SBC) decoder support.

•

pico_btstack_bnep_lwip - Adds Bluetooth Network Encapsulation Protocol (BNEP) support using LwIP.

•

pico_btstack_bnep_lwip_sys_freertos - Adds Bluetooth Network Encapsulation Protocol (BNEP) support using

LwIP with FreeRTOS in NO_SYS=0 mode.

To use BTstack you must add pico_btstack_cyw43 and one or both of pico_btsack_ble and pico_sbtstack_classic to your

application dependencies in your CMakeLists.txt. Additionally, you need to provide a btstack_config.h file in your source

tree and add its location to your include path. For more details, see BlueKitchen’s documentation on how to configure

BTstack and the relevant Bluetooth example code in the pico-examples repository.

The CMake function pico_btstack_make_gatt_header can be used to run the BTstack compile_gatt tool to make a GATT

header file from a BTstack GATT file.

Raspberry Pi Pico C/C++ SDK

2.3. SDK Library Structure 17

2.4. Directory Structure

We have discussed libraries such as pico_stdlib and hardware_gpio above. Imagine you wanted to add some code using

RP2040’s DMA controller to the hello_world example in pico-examples. To do this you need to add a dependency on

another library, hardware_dma, which is not included by default by pico_stdlib (unlike, say, hardware_uart).

You would change your CMakeLists.txt to list both pico_stdlib and hardware_dma as dependencies of the hello_world target

(executable). (Note the line breaks are not required)

target_link_libraries(hello_world

Ê pico_stdlib

Ê hardware_dma

)

And in your source code you would include the DMA hardware library header as such:

#include "hardware/dma.h"

Trying to include this header without listing hardware_dma as a dependency will fail, and this is due to how SDK files are

organised into logical functional units on disk, to make it easier to add functionality in the future.

As an aside, this correspondence of hardware_dma → hardware/dma.h is the convention for all toplevel SDK library headers.

The library is called foo_bar and the associated header is foo/bar.h. Some functions may be provided inline in the

headers, others may be compiled and linked from additional .c files belonging to the library. Both of these require the

relevant hardware_ library to be listed as a dependency, either directly or through some higher-level bundle like

pico_stdlib.



NOTE

Some libraries have additional headers which are located in foo/bar/other.h

You may want to actually find the files in question (although most IDEs will do this for you). The on disk files are actually

split into multiple top-level directories. This is described in the next section.

2.4.1. Locations of Files

Whilst you may be focused on building a binary to run specifically on Raspberry Pi Pico, which uses a RP2040, the SDK

is structured in a more general way. This is for two reasons:

1. To support other future chips in the RP2 family

2. To support testing of your code off device (this is host mode)

The latter is useful for writing and running unit tests, but also as you develop your software, for example your debugging

code or work in progress software might actually be too big or use too much RAM to fit on the device, and much of the

software complexity may be non-hardware-specific.

The code is thus split into top level directories as follows:

Table 1. Top-level

directories

Path Description

src/rp2040/

This contains the hardware_regs and hardware_structs libraries mentioned earlier, which are

specific to RP2040.

Raspberry Pi Pico C/C++ SDK

2.4. Directory Structure 18

Path Description

src/rp2_common/

This contains the hardware_ library implementations for individual hardware components,

and pico_ libraries or library implementations that are closely tied to RP2040 hardware.

This is separate from /src/rp2040 as there may be future revisions of RP2040, or other

chips in the RP2 family, which can use a common SDK and API whilst potentially having

subtly different register definitions.

src/common/

This is code that is common to all builds. This is generally headers providing hardware

abstractions for functionality which are simulated in host mode, along with a lot of the

pico_ library implementations which, to the extent they use hardware, do so only through

the hardware_ abstractions.

src/host/

This is a basic set of replacement SDK library implementations sufficient to get simple

Raspberry Pi Pico applications running on your computer (Raspberry Pi OS, Linux,

macOS or Windows using Cygwin or Windows Subsystem for Linux). This is not

intended to be a fully functional simulator, however it is possible to inject additional

implementations of libraries to provide more complete functionality.

There is a CMake variable PICO_PLATFORM that controls the environment you are building for:

When doing a regular RP2040 build (PICO_PLATFORM=rp2040, the default), you get code from common, rp2_common and rp2040;

when doing a host build (PICO_PLATFROM=host), you get code from common and host.

Within each top-level directory, the libraries have the following structure (reading foo_bar as something like hardware_uart

or pico_time)

top-level_dir/

top-level_dir/foo_bar/include/foo/bar.h # header file

top-level_dir/foo_bar/CMakeLists.txt # build configuration

top-level_dir/foo_bar/bar.c # source file(s)

As a concrete example, we can list the hardware_uart directory under pico-sdk/rp2_common (you may also recall the

hardware_gpio library we looked at earlier):

hardware_uart

├── CMakeLists.txt

├── include

│ÊÊ └── hardware

│ÊÊ └── uart.h

└── uart.c

uart.h contains function declarations and preprocessor defines for the hardware_uart library, as well as some inline

functions that are expected to be particularly amenable to constant folding by the compiler. uart.c contains the

implementations of more complex functions, such as calculating and setting up the divisors for a given UART baud rate.



NOTE

The directory top-level_dir/foo_bar/include is added as an include directory to the INTERFACE library foo_bar, which is

what allows you to include "foo/bar.h" in your application

2.5. Conventions for Library Functions

This section covers some common patterns you will see throughout the SDK libraries, such as conventions for function

Raspberry Pi Pico C/C++ SDK

2.5. Conventions for Library Functions 19

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