/*!
\brief lcd peripheral initialize
\param[in] none
\param[out] none
\retval none
*/
void exmc_lcd_init(void)
{
exmc_norsram_parameter_struct lcd_init_struct;
exmc_norsram_timing_parameter_struct lcd_timing_init_struct;
/* EXMC clock enable */
rcu_periph_clock_enable(RCU_EXMC); // EXMC初始化语句1
/* GPIO clock enable */
rcu_periph_clock_enable(RCU_GPIOD);
rcu_periph_clock_enable(RCU_GPIOE);
/* configure EXMC_D[0~15]*/
/* PD14(EXMC_D0), PD15(EXMC_D1),PD0(EXMC_D2), PD1(EXMC_D3), PD8(EXMC_D13), PD9(EXMC_D14), PD10(EXMC_D15) */
gpio_init(GPIOD, GPIO_MODE_AF_PP, GPIO_OSPEED_50MHZ, GPIO_PIN_0 | GPIO_PIN_1| GPIO_PIN_8 | GPIO_PIN_9 |
GPIO_PIN_10 | GPIO_PIN_14 | GPIO_PIN_15);
/* PE7(EXMC_D4), PE8(EXMC_D5), PE9(EXMC_D6), PE10(EXMC_D7), PE11(EXMC_D8), PE12(EXMC_D9),
PE13(EXMC_D10), PE14(EXMC_D11), PE15(EXMC_D12) */
gpio_init(GPIOE, GPIO_MODE_AF_PP, GPIO_OSPEED_50MHZ, GPIO_PIN_7 | GPIO_PIN_8 | GPIO_PIN_9 |
GPIO_PIN_10 | GPIO_PIN_11 | GPIO_PIN_12 |
GPIO_PIN_13 | GPIO_PIN_14 | GPIO_PIN_15);
/* configure PE2(EXMC_A23) */
gpio_init(GPIOE, GPIO_MODE_AF_PP, GPIO_OSPEED_50MHZ, GPIO_PIN_2);
/* configure NOE and NWE */
gpio_init(GPIOD, GPIO_MODE_AF_PP, GPIO_OSPEED_50MHZ, GPIO_PIN_4 | GPIO_PIN_5);
/* configure EXMC NE0 */
gpio_init(GPIOD, GPIO_MODE_AF_PP, GPIO_OSPEED_50MHZ, GPIO_PIN_7);
lcd_timing_init_struct.asyn_access_mode = EXMC_ACCESS_MODE_A;
lcd_timing_init_struct.syn_data_latency = EXMC_DATALAT_2_CLK;
lcd_timing_init_struct.syn_clk_division = EXMC_SYN_CLOCK_RATIO_DISABLE;
lcd_timing_init_struct.bus_latency = 2;
lcd_timing_init_struct.asyn_data_setuptime = 18;
lcd_timing_init_struct.asyn_address_holdtime = 3;
lcd_timing_init_struct.asyn_address_setuptime = 8;
lcd_init_struct.norsram_region = EXMC_BANK0_NORSRAM_REGION0;
lcd_init_struct.write_mode = EXMC_ASYN_WRITE;
lcd_init_struct.extended_mode = DISABLE;
lcd_init_struct.asyn_wait = DISABLE;
lcd_init_struct.nwait_signal = DISABLE;
lcd_init_struct.memory_write = ENABLE;
lcd_init_struct.nwait_config = EXMC_NWAIT_CONFIG_BEFORE;
lcd_init_struct.wrap_burst_mode = DISABLE;
lcd_init_struct.nwait_polarity = EXMC_NWAIT_POLARITY_LOW;
lcd_init_struct.burst_mode = DISABLE;
lcd_init_struct.databus_width = EXMC_NOR_DATABUS_WIDTH_16B;
lcd_init_struct.memory_type = EXMC_MEMORY_TYPE_SRAM;
lcd_init_struct.address_data_mux = DISABLE;
lcd_init_struct.read_write_timing = &lcd_timing_init_struct;
lcd_init_struct.write_timing = &lcd_timing_init_struct;
exmc_norsram_init(&lcd_init_struct); // EXMC初始化语句2
exmc_norsram_enable(EXMC_BANK0_NORSRAM_REGION0); // EXMC初始化语句3
}void exmc_lcd_init(void)
{
exmc_norsram_parameter_struct lcd_init_struct;
exmc_norsram_timing_parameter_struct lcd_timing_init_struct;
/* EXMC clock enable */
// rcu_periph_clock_enable(RCU_EXMC); // EXMC初始化语句1
/* 省略 */
// exmc_norsram_init(&lcd_init_struct); // EXMC初始化语句2
// exmc_norsram_enable(EXMC_BANK0_NORSRAM_REGION0); // EXMC初始化语句3
}/*!
\brief enable the peripherals clock
\param[in] periph: RCU peripherals, refer to rcu_periph_enum
only one parameter can be selected which is shown as below:
\arg RCU_GPIOx (x=A,B,C,D,E,F,G): GPIO ports clock
\arg RCU_AF : alternate function clock
\arg RCU_CRC: CRC clock
\arg RCU_DMAx (x=0,1): DMA clock
\arg RCU_ENET: ENET clock(CL series available)
\arg RCU_ENETTX: ENETTX clock(CL series available)
\arg RCU_ENETRX: ENETRX clock(CL series available)
\arg RCU_USBD: USBD clock(HD,XD series available)
\arg RCU_USBFS: USBFS clock(CL series available)
\arg RCU_EXMC: EXMC clock
\arg RCU_TIMERx (x=0,1,2,3,4,5,6,7,8,9,10,11,12,13,TIMER8..13 are not available for HD series): TIMER clock
\arg RCU_WWDGT: WWDGT clock
\arg RCU_SPIx (x=0,1,2): SPI clock
\arg RCU_USARTx (x=0,1,2): USART clock
\arg RCU_UARTx (x=3,4): UART clock
\arg RCU_I2Cx (x=0,1): I2C clock
\arg RCU_CANx (x=0,1,CAN1 is only available for CL series): CAN clock
\arg RCU_PMU: PMU clock
\arg RCU_DAC: DAC clock
\arg RCU_RTC: RTC clock
\arg RCU_ADCx (x=0,1,2,ADC2 is not available for CL series): ADC clock
\arg RCU_SDIO: SDIO clock(not available for CL series)
\arg RCU_CTC: CTC clock
\arg RCU_BKPI: BKP interface clock
\param[out] none
\retval none
*/
void rcu_periph_clock_enable(rcu_periph_enum periph)
{
RCU_REG_VAL(periph) |= BIT(RCU_BIT_POS(periph));
}i2c_gpio_config(); /* configure GPIO */
i2c_config(); /* configure I2C */
i2c_eeprom_init(); /* initialize EEPROM */
exmc_lcd_init(); /* configure the EXMC access mode */
delay_1ms(50);
rcu_periph_clock_disable(RCU_EXMC);
MPL_Init();
可以发现EXMC模块使用的总线是AHB，和I2C模块（使用总线为APB1）并没有在一个区域，应该不是总线问题导致的互相影响。
再来看一下GD32F303的时钟单元。下图是GD32F303的时钟树结构：
可以看到，系统时钟CK_SYS先经过了AHB预分频器，然后给到EXMC模块的时钟CK_EXMC；同时AHB预分频器之后还给到APB1预分频器，然后才给到PCLK1，提供给APB1总线上的外设使用。
难道是EXMC模块的时钟使能操作影响到了AHB时钟的分频，导致I2C总线的传输速度收到影响，从而导致数据读写操作失败？
从理论上来讲，应该不会发生这种情况的，后端的时钟使用与否不会影响到前面分频器的工作。
继续详细查看用户手册ing。
忽然间，在芯片手册里，发现了GPIO引脚定义表格，发现PB7引脚的第二功能同时具有I2C0_SDA功能和EXMC_NADV功能！
难道是引脚冲突了？EXMC_NADV功能只能用PB7，而例程里的I2C0初始化部分，也确实用了PB7。
/*!
\brief configure the GPIO ports
\param[in] none
\param[out] none
\retval none
*/
void i2c_gpio_config(void)
{
/* enable GPIOB clock */
rcu_periph_clock_enable(RCU_GPIOB);
/* enable I2C0 clock */
rcu_periph_clock_enable(RCU_I2C0);
/* connect PB6 to I2C0_SCL */
/* connect PB7 to I2C0_SDA */
gpio_init(GPIOB, GPIO_MODE_AF_OD, GPIO_OSPEED_50MHZ, GPIO_PIN_6 | GPIO_PIN_7);
}void i2c_gpio_config(void)
{
/* enable GPIOB clock */
rcu_periph_clock_enable(RCU_GPIOB);
/* enable I2C0 clock */
rcu_periph_clock_enable(RCU_I2C0);
rcu_periph_clock_enable(RCU_AF);
/* connect PB8 to I2C0_SCL */
/* connect PB9 to I2C0_SDA */
gpio_pin_remap_config(GPIO_I2C0_REMAP, ENABLE);
gpio_init(GPIOB, GPIO_MODE_AF_OD, GPIO_OSPEED_50MHZ, GPIO_PIN_8 | GPIO_PIN_9);
}
然后调试验证，I2C读写正常，屏幕显示正常。
至此，硬件I2C读写异常问题完美解决。
导致问题出现的原因是开发板在不同模块的例程上都用到了PB7，从而导致两个功能无法同时使用。
进行引脚功能remap即可解决该问题。
---------------------
作者：blust5
链接：https://bbs.21ic.com/icview-3300846-1-1.html
来源：21ic.com
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