Linux中SPI

news2024/11/25 20:29:33

参考资料

https://www.cnblogs.com/aaronLinux/p/6219146.html

1.SPI
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2.SPI传输
2.1传输示例

首先，CS0拉低选中的SPI Flash ,
然后在每个时钟周期，
DO输出对应的电平。
SPI FLASH会在每个时钟的上升沿读取D0的电平。

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2.2SPI模式
根据SCK的电平以及数据在第一个跳变沿还是第二个跳变沿传输，SPI传输总共有四种模式。

3.SPI总线设备驱动模型

SPI系统中设涉及两类硬件：
SPI控制器
SPI设备

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spi控制器有驱动程序，提供spi的传输能力。
spi设备也有自己的驱动程序，提供spi设备的访问能力。
4.spi设备驱动框架图

SPI驱动程序由spi_master及spi_device组成
spi_master是在设备树中定义的spi master及master
下边的device信息；当左边drive中的of_device_id和设备树中的compatible参数匹配的时候，会调用driver中的prboe函数，probe函数会生成master，还会生成spi_device。
spi设备左边包括一个spi驱动，当其中的of_device_id和spi_device匹配时，会调用左边driver中的probe函数。

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4.1SPI控制器驱动程序
基于平台总线设备驱动模型实现。在probe函数中除了生成spi_master，还会创建spi_device结构体。

4.2SPI设备驱动程序

左边是spi_drive,里边有id_table表示能支持哪些SPI设备，有probe函数。
右边是spi_device,用来描述spi设备，可以来自设备树或者c文件

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5.spi设备树处理过程
5.1spi_device

/**
 * struct spi_device - Master side proxy for an SPI slave device
 * @dev: Driver model representation of the device.
 * @master: SPI controller used with the device.
 * @max_speed_hz: Maximum clock rate to be used with this chip
 *	(on this board); may be changed by the device's driver.
 *	The spi_transfer.speed_hz can override this for each transfer.
 * @chip_select: Chipselect, distinguishing chips handled by @master.
 * @mode: The spi mode defines how data is clocked out and in.
 *	This may be changed by the device's driver.
 *	The "active low" default for chipselect mode can be overridden
 *	(by specifying SPI_CS_HIGH) as can the "MSB first" default for
 *	each word in a transfer (by specifying SPI_LSB_FIRST).
 * @bits_per_word: Data transfers involve one or more words; word sizes
 *	like eight or 12 bits are common.  In-memory wordsizes are
 *	powers of two bytes (e.g. 20 bit samples use 32 bits).
 *	This may be changed by the device's driver, or left at the
 *	default (0) indicating protocol words are eight bit bytes.
 *	The spi_transfer.bits_per_word can override this for each transfer.
 * @irq: Negative, or the number passed to request_irq() to receive
 *	interrupts from this device.
 * @controller_state: Controller's runtime state
 * @controller_data: Board-specific definitions for controller, such as
 *	FIFO initialization parameters; from board_info.controller_data
 * @modalias: Name of the driver to use with this device, or an alias
 *	for that name.  This appears in the sysfs "modalias" attribute
 *	for driver coldplugging, and in uevents used for hotplugging
 * @cs_gpio: gpio number of the chipselect line (optional, -ENOENT when
 *	when not using a GPIO line)
 *
 * @statistics: statistics for the spi_device
 *
 * A @spi_device is used to interchange data between an SPI slave
 * (usually a discrete chip) and CPU memory.
 *
 * In @dev, the platform_data is used to hold information about this
 * device that's meaningful to the device's protocol driver, but not
 * to its controller.  One example might be an identifier for a chip
 * variant with slightly different functionality; another might be
 * information about how this particular board wires the chip's pins.
 */
struct spi_device {
	struct device		dev;
	struct spi_master	*master;
	u32			max_speed_hz;/* 该设备能支持的spi时钟最大值 */
	u8			chip_select;/* 是对应的spi_master下边的第几个设备 */
	u8			bits_per_word;/* 每个基本的spi传输涉及多少位 */
	u16			mode; /*spi_chpa  spi_cpol组合起来得到spi传输的四种模式 */
#define	SPI_CPHA	0x01			/* clock phase */
#define	SPI_CPOL	0x02			/* clock polarity */
#define	SPI_MODE_0	(0|0)			/* (original MicroWire) */
#define	SPI_MODE_1	(0|SPI_CPHA)
#define	SPI_MODE_2	(SPI_CPOL|0)
#define	SPI_MODE_3	(SPI_CPOL|SPI_CPHA)
#define	SPI_CS_HIGH	0x04			/* chipselect active high? */
#define	SPI_LSB_FIRST	0x08			/* per-word bits-on-wire */
#define	SPI_3WIRE	0x10			/* SI/SO signals shared */
#define	SPI_LOOP	0x20			/* loopback mode */
#define	SPI_NO_CS	0x40			/* 1 dev/bus, no chipselect */
#define	SPI_READY	0x80			/* slave pulls low to pause */
#define	SPI_TX_DUAL	0x100			/* transmit with 2 wires */
#define	SPI_TX_QUAD	0x200			/* transmit with 4 wires */
#define	SPI_RX_DUAL	0x400			/* receive with 2 wires */
#define	SPI_RX_QUAD	0x800			/* receive with 4 wires */
	int			irq;
	void			*controller_state;
	void			*controller_data;
	char			modalias[SPI_NAME_SIZE];
	int			cs_gpio;	/* chip select gpio */

	/* the statistics */
	struct spi_statistics	statistics;

	/*
	 * likely need more hooks for more protocol options affecting how
	 * the controller talks to each chip, like:
	 *  - memory packing (12 bit samples into low bits, others zeroed)
	 *  - priority
	 *  - drop chipselect after each word
	 *  - chipselect delays
	 *  - ...
	 */
};

5.2设备树中的spi节点

    spi4 {
        compatible = "spi-gpio";/* 这个属性很关键，因为根据这个属性找到spi_master */
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_spi4>;
        pinctrl-assert-gpios = <&gpio5 8 GPIO_ACTIVE_LOW>;
        status = "okay";
        gpio-sck = <&gpio5 11 0>;
        gpio-mosi = <&gpio5 10 0>;
        cs-gpios = <&gpio5 7 0>;
        num-chipselects = <1>;
        #address-cells = <1>;/* 这个SPI Master下的SPI设备，需要多少个cell来表述它的片选引脚 */
        #size-cells = <0>; /* 这个必须设置为0 */
		/* gpio_spi是spi_master 下边的device节点 */
        gpio_spi: gpio_spi@0 {
            compatible = "fairchild,74hc595";/* 根据它找到spi device驱动 */
            gpio-controller;
            #gpio-cells = <2>;
            reg = <0>;/* 使用哪个片选引脚 */
            registers-number = <1>;
            registers-default = /bits/ 8 <0x57>;
            spi-max-frequency = <10000>;/* 该设备支持的最大spi时钟 */
        };
    };