[原創(chuàng)]STM32硬件I2C和軟件模擬I2C實(shí)現(xiàn)對(duì)比

ID:946578 · 發(fā)表于 2021-6-29 12:09

一、概述

I2C是一種占用管腳少、傳送可靠和傳輸速率較好的低速總線，在嵌入式設(shè)備中被廣泛使用到。I2C 接口接收和發(fā)送數(shù)據(jù)，并將數(shù)據(jù)從串行轉(zhuǎn)換成并行，或并行轉(zhuǎn)換成串行。可以開啟或禁止中斷。接口通過數(shù)據(jù)引腳(SDA)和時(shí)鐘引腳(SCL)連接到I2C總線。允許連接到標(biāo)準(zhǔn)(高至100 kHz)或快速(高至400 kHz) I2C總線。

STM32一般有2-3組硬件I2C，以STM32F103CB為例，其硬件I2C情況如下——

I2C編號(hào)	I2C名稱	對(duì)應(yīng)管腳
1	I2C1	PB6, PB7
2	I2C2	PB10, PB11

所謂硬件I2C，即STM32芯片設(shè)計(jì)了SDA/SCL兩個(gè)管腳內(nèi)部已符合觸發(fā)I2C的時(shí)序、協(xié)議、仲裁和定時(shí)等功能塊，軟件開發(fā)人員只需調(diào)用簡(jiǎn)單的API即可方便使用I2C功能了。

此外，由于硬件設(shè)計(jì)的原因，需要使用很多個(gè)I2C或不巧硬件I2C管腳被占用，此時(shí)就需要通過GPIO軟件模擬I2C，它是通過軟件來實(shí)現(xiàn)I2C的時(shí)序、協(xié)議、仲裁和定時(shí)等完整的機(jī)制。

原理和概念部分不再贅述，大家很容易在網(wǎng)上找到各類相關(guān)資料進(jìn)行了解和學(xué)習(xí)，今天我們?cè)敿?xì)陳述具體實(shí)現(xiàn)過程和比較兩者的一些差異，主要以代碼作為表述形式。

二、硬件I2C的實(shí)現(xiàn)

硬件I2C調(diào)用的api接口均在stm32f10x_i2c.c文件中，通過這些API，我們需要實(shí)現(xiàn)

(1) I2C的初始化；

(2) I2C讀和寫的接口函數(shù)，供外部調(diào)用。

初始化代碼如下——

#define CPS1848_I2C I2C2

#define CHECK_BUSY(checkflag,busyendflag,dwCnt, dwTimeOut) \

for (dwCnt =0; dwCnt< dwTimeOut; dwCnt++) \

{ \

if((checkflag) == (busyendflag))\

{\

break;\

}\

}

#define CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut) \

if (dwBusyCount >= dwTimeOut) \

{ \

return ERR_WAIT_BUSY; \

}

// I2C 外設(shè)(CPS1848)初始化

void I2C_CPS1848_Init(BYTE ucBoardAddr)

{

//GPIO初始化

GPIO_InitTypeDef GPIO_InitStructure;

I2C_InitTypeDef I2C_InitStructure;

/* 使能與 I2Cx 引腳的GPIO的時(shí)鐘 */

RCC_APB2PeriphClockCmd(CPS1848_I2C_SCL_GPIO_CLK | CPS1848_I2C_SDA_GPIO_CLK, ENABLE);

/* 使能 I2Cx 外設(shè)時(shí)鐘 */

RCC_APB1PeriphClockCmd(CPS1848_I2C_CLK, ENABLE);

/* Reset I2Cx IP */

RCC_APB1PeriphResetCmd(CPS1848_I2C_CLK, ENABLE);

/* Release reset signal of I2Cx IP */

RCC_APB1PeriphResetCmd(CPS1848_I2C_CLK, DISABLE);

/* I2Cx_SCL */

GPIO_InitStructure.GPIO_Pin = CPS1848_I2C_SCL_PIN;

GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_OD;

GPIO_Init(CPS1848_I2C_SCL_PORT, &GPIO_InitStructure);

/* I2Cx_SDA*/

GPIO_InitStructure.GPIO_Pin = CPS1848_I2C_SDA_PIN;

GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_OD;

GPIO_Init(CPS1848_I2C_SDA_PORT, &GPIO_InitStructure);

//模式初始化

/* I2Cx 配置 */

I2C_InitStructure.I2C_Mode = I2C_Mode_SMBusHost/*I2C_Mode_I2C */;

/* 高電平數(shù)據(jù)穩(wěn)定，低電平數(shù)據(jù)變化 SCL 時(shí)鐘線的占空比 */

I2C_InitStructure.I2C_DutyCycle = I2C_DutyCycle_2;

I2C_InitStructure.I2C_OwnAddress1 = (ucBoardAddr << 1);

I2C_InitStructure.I2C_Ack = I2C_Ack_Enable ;

/* I2Cx的尋址模式 */

I2C_InitStructure.I2C_AcknowledgedAddress = I2C_AcknowledgedAddress_7bit;

/* 通信速率 */

I2C_InitStructure.I2C_ClockSpeed = 100000; //Standard-mode devices at 100 Kbps

/* I2Cx 初始化 */

I2C_Init(CPS1848_I2C, &I2C_InitStructure);

/* 使能 I2Cx 外設(shè)*/

I2C_Cmd(CPS1848_I2C, ENABLE);

/*使能或者失能指定的I2C應(yīng)答功能*/

I2C_AcknowledgeConfig(CPS1848_I2C, ENABLE);

}

I2C的讀操作實(shí)現(xiàn)如下——

BYTE I2C_CPS1848_Read(uint8_t cps1848_index, uint32_t RegAddr, uint32_t *pdwData)

{

volatile uint32_t i2cdata = 0;

uint16_t NumByteToRead = 4;

DWORD dwBusyCount = 0;

const DWORD dwTimeOut = 1000;

CHECK_POINTER_RET_ERR(pdwData);

/* 等待busy位 */

dwBusyCount = 0;

CHECK_BUSY(I2C_GetFlagStatus(CPS1848_I2C, I2C_FLAG_BUSY), RESET, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* Enable Acknowledgement to be ready for another reception

necessary...*/

I2C_AcknowledgeConfig(CPS1848_I2C, ENABLE);

/* 發(fā)送開始信號(hào) */

I2C_GenerateSTART(CPS1848_I2C, ENABLE);

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_MODE_SELECT), SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送目標(biāo)地址 : Reset the address bit0 for write*/

I2C_Send7bitAddress(CPS1848_I2C, ((CPS1848_I2C_ADDR+cps1848_index) << 1), I2C_Direction_Transmitter);

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_TRANSMITTER_MODE_SELECTED),

SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送寄存器地址--高8bit */

I2C_SendData(CPS1848_I2C, ((RegAddr>>18) & 0xff));

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_BYTE_TRANSMITTED), SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送寄存器地址--中8bit */

I2C_SendData(CPS1848_I2C, ((RegAddr>>10) & 0xff));

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_BYTE_TRANSMITTED), SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送寄存器地址--低8bit */

I2C_SendData(CPS1848_I2C, ((RegAddr>>2) & 0xff));

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_BYTE_TRANSMITTED), SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 開始讀取數(shù)據(jù) */

I2C_GenerateSTART(CPS1848_I2C, ENABLE);

/* Test on EV5 and clear it */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_MODE_SELECT), SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送讀取的地址: Set the address bit0 for read*/

I2C_Send7bitAddress(CPS1848_I2C, ((CPS1848_I2C_ADDR+cps1848_index) << 1) | 0x01, I2C_Direction_Receiver);

/* Test on EV6 and clear it */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_RECEIVER_MODE_SELECTED), SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

while(NumByteToRead--)

{

if (0 == NumByteToRead)

{

/* 最后一個(gè)數(shù)據(jù)了，發(fā)送非應(yīng)答信號(hào)(Disable Acknowledgement)，結(jié)束傳輸；*/

I2C_AcknowledgeConfig(CPS1848_I2C, DISABLE);

/* 發(fā)送停止位 */

I2C_GenerateSTOP(CPS1848_I2C, ENABLE);

}

/* Test on EV7 and clear it */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_BYTE_RECEIVED), SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

i2cdata = (i2cdata<<8) | (I2C_ReceiveData(CPS1848_I2C));

}

*pdwData = i2cdata;

/* Enable Acknowledgement to be ready for another reception */

I2C_AcknowledgeConfig(CPS1848_I2C, ENABLE);

return ERR_SUCCESS;

}

I2C的寫操作實(shí)現(xiàn)如下——

BYTE I2C_CPS1848_Write(uint8_t cps1848_index, uint32_t RegAddr, uint32_t RegData)

{

DWORD dwBusyCount = 0;

const DWORD dwTimeOut = 10000;

/* 等待busy位 */

dwBusyCount = 0;

CHECK_BUSY(I2C_GetFlagStatus(CPS1848_I2C, I2C_FLAG_BUSY),

RESET, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送開始信號(hào) */

I2C_GenerateSTART(CPS1848_I2C, ENABLE);

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_MODE_SELECT),

SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送目標(biāo)地址 */

I2C_Send7bitAddress(CPS1848_I2C, ((CPS1848_I2C_ADDR+cps1848_index) << 1), I2C_Direction_Transmitter);

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_TRANSMITTER_MODE_SELECTED),

SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送寄存器地址--高8bit */

I2C_SendData(CPS1848_I2C, ((RegAddr>>18) & 0xff));

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_BYTE_TRANSMITTED),

SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送寄存器地址--中8bit */

I2C_SendData(CPS1848_I2C, ((RegAddr>>10) & 0xff));

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_BYTE_TRANSMITTED),

SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送寄存器地址--低8bit */

I2C_SendData(CPS1848_I2C, ((RegAddr>>2) & 0xff));

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_BYTE_TRANSMITTED),

SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送數(shù)據(jù) */

I2C_SendData(CPS1848_I2C, ((RegData>>24) & 0xff));

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_BYTE_TRANSMITTED),

SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送數(shù)據(jù) */

I2C_SendData(CPS1848_I2C, ((RegData>>16) & 0xff));

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_BYTE_TRANSMITTED),

SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送數(shù)據(jù) */

I2C_SendData(CPS1848_I2C, ((RegData>>8) & 0xff));

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_BYTE_TRANSMITTED),

SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送數(shù)據(jù) */

I2C_SendData(CPS1848_I2C, ((RegData) & 0xff));

/* 等待握手 */

dwBusyCount = 0;

CHECK_BUSY(I2C_CheckEvent(CPS1848_I2C, I2C_EVENT_MASTER_BYTE_TRANSMITTED),

SUCCESS, dwBusyCount, dwTimeOut);

CHECK_WAIT_BUSY(dwBusyCount, dwTimeOut);

/* 發(fā)送停止位 */

I2C_GenerateSTOP(CPS1848_I2C, ENABLE);

return ERR_SUCCESS;

}

三、軟件模擬I2C的實(shí)現(xiàn)

GPIO軟件模擬I2C的實(shí)現(xiàn)中，首先是初始化；其次，由于沒有現(xiàn)存的I2C時(shí)序、協(xié)議、控制等API接口，這些就需要我們根據(jù)I2C協(xié)議進(jìn)行嚴(yán)格實(shí)現(xiàn)，具體詳見附件。

四、兩者的差異

硬件I2C實(shí)現(xiàn)很簡(jiǎn)潔，且流程中延時(shí)、應(yīng)答等機(jī)制都無需軟件參與，只需做好正確配置和調(diào)用即可；軟件模擬I2C的實(shí)現(xiàn)需要非常完備，且需要嚴(yán)格按照I2C協(xié)議進(jìn)行編寫，嚴(yán)格控制延時(shí)、應(yīng)答、判定等。

了解兩者之間的差異，并且能夠?qū)崿F(xiàn)兩種I2C的使用，會(huì)極大加深我們對(duì)于I2C的理解和熟練程度，非常有益。

C文件51hei下載:

gpio_i2c_bsp.rar (1.31 KB, 下載次數(shù): 50)

ID:946578 · 發(fā)表于 2021-6-29 12:13

由于篇幅緣故，沒有將所有代碼貼在文中，而放在附件中了。

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[原創(chuàng)]STM32硬件I2C和軟件模擬I2C實(shí)現(xiàn)對(duì)比

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