使用Platformio平臺(tái)的libopencm3開發(fā)框架來開發(fā)STM32G0，下面介紹SPI接口的基本使用。

1 SPI配置

以下為設(shè)置SPI1，引腳映射為PA5\\6\\7，使用軟件控制CS-PA4;

1/* Enable SPI1 Periph and gpio clocks */
 2    rcc_periph_clock_enable(RCC_SPI1);
 3    rcc_periph_clock_enable(RCC_GPIOA);
 4
 5/* Configure GPIOs:
 6     * 
 7     * SCK=PA5
 8     * MOSI=PA7 
 9     * MISO=PA6
10     * 
11     * for SD card
12     * SDCS PA4
13     */
14
15//MOSI & SCK & MISO
16gpio_mode_setup(GPIOA, GPIO_MODE_AF, GPIO_PUPD_NONE,GPIO5|GPIO7|GPIO6);
17gpio_set_af(GPIOA,GPIO_AF0,GPIO5|GPIO7|GPIO6);
18gpio_set_output_options(GPIOA, GPIO_OTYPE_PP,GPIO_OSPEED_LOW,GPIO5|GPIO7|GPIO6);
19
20//SDCS 
21gpio_mode_setup(GPIOA,GPIO_MODE_OUTPUT,GPIO_PUPD_NONE,GPIO4);
22gpio_set(GPIOA,GPIO4);
23
24/* Reset SPI, SPI_CR1 register cleared, SPI is disabled */
25spi_reset(SPI1);
26
27/* Set up SPI in Master mode with:
28   * Clock baud rate
29   * Clock polarity
30   * Clock phase
31   * Frame format MSB
32   */
33spi_init_master(SPI1, SPI_CR1_BAUDRATE_FPCLK_DIV_128, 
34                SPI_CR1_CPOL_CLK_TO_0_WHEN_IDLE,
35                SPI_CR1_CPHA_CLK_TRANSITION_1,
36                SPI_CR1_MSBFIRST);
37
38    spi_set_data_size(SPI1,SPI_CR2_DS_8BIT);
39    spi_set_full_duplex_mode(SPI1);
40
41/*
42   * Set NSS management to software.
43   *
44   * Note:
45   * Setting nss high is very important, even if we are controlling 
46   * the GPIO
47   * ourselves this bit needs to be at least set to 1, otherwise the spi
48   * peripheral will not send any data out.
49   */
50spi_enable_software_slave_management(SPI1);
51spi_set_nss_high(SPI1);
52
53/* Enable SPI1 periph. */
54spi_enable(SPI1);

設(shè)置流程：打開外設(shè)時(shí)鐘-> 設(shè)置SPI引腳 -> CS引腳 -> 配置SPI模式包括SPI速度、CPOL\\CPHA -> SPI傳輸數(shù)據(jù)位數(shù) -> NSS配置 -> SPI使能；

2 SPI讀寫

• 寫入后讀取

1uint16_t spi_xfer(uint32_t spi, uint16_t data)

• 發(fā)送

1void spi_send(uint32_t spi, uint16_t data)
2

• 接收

1uint16_t spi_read(uint32_t spi)

• 對(duì)于8bit的發(fā)送和接收在STM32G0上，libopencm3庫需要使用如下接口：

1spi_send8();
2spi_read8();

3 說明

默認(rèn)配置的SPI時(shí)鐘是連續(xù)的，波形如下：

在某些時(shí)候需要在幀之間有些空隙，可以設(shè)置CR2寄存器的NSSP位或者直接在發(fā)送前進(jìn)行延時(shí)：

1SPI_CR2(SPI1) |= SPI_CR2_NSSP; //NSSP

波形如下：