I2C总线协议学习笔记
加入技术交流群
- static int mpc_write(struct mpc_i2c *i2c, int target,
const u8 * data, int length, int restart) - {
int i; unsigned timeout = i2c->adap.timeout; u32 flags = restart ? CCR_RSTA : 0; //以防万一，保证I2C模块使能起来 if (!restart) writeccr(i2c, CCR_MEN); //写了I2CCR[CCR_MSTA]，触发CPU发起START信号 writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA | CCR_MTX | flags); //CPU发送一个字节，slave I2C addr和0 (写操作bit) writeb((target << 1), i2c->base + MPC_I2C_DR); if (i2c_wait(i2c, timeout, 1) < 0) //等待slave 发ACK return -1; for (i = 0; i < length; i++) { writeb(data[i], i2c->base + MPC_I2C_DR); //CPU接着发数据，包括reg addr和data if (i2c_wait(i2c, timeout, 1) < 0) //等待slave 发ACK return -1; } return 0; - }
- static int i2c_wait(struct mpc_i2c *i2c, unsigned timeout, int writing)
- {
unsigned long orig_jiffies = jiffies; u32 x; int result = 0; if (i2c->irq == 0) { //循环读I2CSR，直到I2CSR[MIF]置1 while (!(readb(i2c->base + MPC_I2C_SR) & CSR_MIF)) { schedule(); if (time_after(jiffies, orig_jiffies + timeout)) { pr_debug("I2C: timeoutn"); writeccr(i2c, 0); result = -EIO; break; } } x = readb(i2c->base + MPC_I2C_SR); writeb(0, i2c->base + MPC_I2C_SR); } else { result = wait_event_interruptible_timeout(i2c->queue, (i2c->interrupt & CSR_MIF), timeout * HZ); if (unlikely(result < 0)) { pr_debug("I2C: wait interruptedn"); writeccr(i2c, 0); } else if (unlikely(!(i2c->interrupt & CSR_MIF))) { pr_debug("I2C: wait timeoutn"); writeccr(i2c, 0); result = -ETIMEDOUT; } x = i2c->interrupt; i2c->interrupt = 0; } if (result < 0) return result; if (!(x & CSR_MCF)) { pr_debug("I2C: unfinishedn"); return -EIO; } if (x & CSR_MAL) { //仲裁失败 pr_debug("I2C: MALn"); return -EIO; } if (writing && (x & CSR_RXAK)) {//写后没收到ACK pr_debug("I2C: No RXAKn"); writeccr(i2c, CCR_MEN); return -EIO; } return 0; - }
- static int mpc_read(struct mpc_i2c *i2c, int target,
u8 * data, int length, int restart) - {
unsigned timeout = i2c->adap.timeout; int i; u32 flags = restart ? CCR_RSTA : 0; //以防万一，保证I2C模块使能 if (!restart) writeccr(i2c, CCR_MEN); //注意这里，再次把CCR_MSTA置1，再触发 START writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA | CCR_MTX | flags); //CPU发送slave I2C addr和读操作1 writeb((target << 1) | 1, i2c->base + MPC_I2C_DR);
if (i2c_wait(i2c, timeout, 1) < 0) return -1; if (length) { if (length == 1) writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA | CCR_TXAK); else //为什么不置 TXAK writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA); readb(i2c->base + MPC_I2C_DR); } for (i = 0; i < length; i++) { if (i2c_wait(i2c, timeout, 0) < 0) return -1; //注意这里TXAK置1，表示CPU每收到1byte数据后，会发送ACK if (i == length - 2) writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA | CCR_TXAK); //注意这里CCR_MSTA [1->0] CPU会触发STOP if (i == length - 1) writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_TXAK); data[i] = readb(i2c->base + MPC_I2C_DR); } return length; - }
评论