对Socket CAN的理解（5）——【Socket CAN控制器的初始化过程】

转载请注明出处：http://blog.csdn.net/Righthek 谢谢！

对于一般的CAN模块，进行初始化时，最关键的是下面两步：

1、  配置CAN的位时序；

2、  配置CAN的消息报文；

以下，我们来具体分析上面提到的关键两步。

一、初始化步骤：

1、  第一步，进入初始化模式。在CAN控制寄存器中，将Init位置1；

2、  第二步，在CAN控制寄存器中，将CCE位置1；

3、  第三步，等待Init位置1。此步聚为了确保已经进入初始化模式；

4、  第四步。将位时序的值写入到位时序寄存器（BTR）中；

5、  第五步，将CCE和Init位置为0；

6、  第六步，等待清除Init位。此步聚为了确保已经退出初始化模式；

解释完CAN的初始化步骤后，我们来看看代码实现：

我们先初始化一个CAN的位时序常量。

/* CAN Bittiming constants as per D_CAN specs */

static structcan_bittiming_const d_can_bittiming_const = {

.name = D_CAN_DRV_NAME,

.tseg1_min = 1,                 /* Time segment 1 = prop_seg + phase_seg1 */

.tseg1_max = 16,

.tseg2_min = 1,                 /* Time segment 2 = phase_seg2 */

.tseg2_max = 8,

.sjw_max = 4,

.brp_min = 1,

.brp_max = 1024,    /* 6-bit BRP field + 4-bit BRPE field*/

.brp_inc = 1,

};

在打开CAN设置时，进行初始化。初始化完毕之后，恢复正常模式。使能收发I/O控制引脚。最后配置消息报文。代码例如以下：

static void d_can_init(structnet_device *dev)

{

struct d_can_priv *priv =netdev_priv(dev);

u32 cnt;

netdev_dbg(dev, "resetting d_can...\n");

d_can_set_bit(priv, D_CAN_CTL,D_CAN_CTL_SWR);

/* Enterinitialization mode by setting the Init bit */

d_can_set_bit(priv, D_CAN_CTL,D_CAN_CTL_INIT);

/* enableautomatic retransmission */

d_can_set_bit(priv, D_CAN_CTL,D_CAN_CTL_ENABLE_AR);

/* Set theConfigure Change Enable ( CCE) bit */

d_can_set_bit(priv, D_CAN_CTL,D_CAN_CTL_CCE);

/* Wait forthe Init bit to get set */

cnt = D_CAN_WAIT_COUNT;

while (!d_can_get_bit(priv, D_CAN_CTL,D_CAN_CTL_INIT) && cnt != 0) {

--cnt;

udelay(10);

}

/* setbittiming params */

d_can_set_bittiming(dev);

d_can_clear_bit(priv, D_CAN_CTL,D_CAN_CTL_INIT | D_CAN_CTL_CCE);

/* Wait for the Init bit to get clear*/

cnt = D_CAN_WAIT_COUNT;

while (d_can_get_bit(priv, D_CAN_CTL,D_CAN_CTL_INIT) && cnt != 0) {

--cnt;

udelay(10);

}

if (priv->can.ctrlmode &(CAN_CTRLMODE_LOOPBACK |

CAN_CTRLMODE_LISTENONLY))

d_can_test_mode(dev);

else

/* normal mode*/

d_can_write(priv, D_CAN_CTL,D_CAN_CTL_EIE | D_CAN_CTL_IE1 |

D_CAN_CTL_IE0);

/* Enable TXand RX I/O Control pins */

d_can_write(priv, D_CAN_TIOC,D_CAN_TIOC_FUNC);

d_can_write(priv, D_CAN_RIOC, D_CAN_RIOC_FUNC);

/* configuremessage objects */

d_can_configure_msg_objects(dev);

/* set a LECvalue so that we can check for updates later */

d_can_write(priv, D_CAN_ES,LEC_UNUSED);

}

运行完第一、第二步之后。设置位时序的參数。代码例如以下：

static intd_can_set_bittiming(struct net_device *dev)

{

struct d_can_priv *priv =netdev_priv(dev);

const struct can_bittiming *bt =&priv->can.bittiming;

u32 can_btc;

can_btc = ((bt->phase_seg2 - 1)& 0x7) << D_CAN_BTR_TSEG2_SHIFT;

can_btc |= ((bt->phase_seg1 +bt->prop_seg - 1)

& 0xF) <<D_CAN_BTR_TSEG1_SHIFT;

can_btc |= ((bt->sjw - 1) & 0x3)<< D_CAN_BTR_SJW_SHIFT;

/* Ten bitscontains the BRP, 6 bits for BRP and upper 4 bits for brpe*/

can_btc |= ((bt->brp - 1) &0x3F) << D_CAN_BTR_BRP_SHIFT;

can_btc |= ((((bt->brp - 1) >>6) & 0xF) << D_CAN_BTR_BRPE_SHIFT);

d_can_write(priv, D_CAN_BTR, can_btc);

netdev_info(dev, "setting CAN BT =%#x\n", can_btc);

return 0;

}

以上内容并非Linux CAN的驱动初始化过程，仅仅是属于当中的一部分。更详细地说，是针对CAN控制器的初始化过程。

转载请注明出处：http://blog.csdn.net/Righthek 谢谢！