linux CAN编程(二) |
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转载自:https://blog.csdn.net/qwaszx523/article/details/54984544 /** * struct can_frame - basic CAN frame structure * @can_id: CAN ID of the frame and CAN_*_FLAG flags, see canid_t definition * @can_dlc: frame payload length in byte (0 .. 8) aka data length code * N.B. the DLC field from ISO 11898-1 Chapter 8.4.2.3 has a 1:1 * mapping of the 'data length code' to the real payload length * @data: CAN frame payload (up to 8 byte) */ struct can_frame { canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */ __u8 can_dlc; /* frame payload length in byte (0 .. CAN_MAX_DLEN) */ __u8 data[CAN_MAX_DLEN] __attribute__((aligned(8))); }; can_id定义如下所示,是一个无符号的32位整形数 typedef __u32 canid_t; can_id数据组织形式如下 /* * Controller Area Network Identifier structure * * bit 0-28 : CAN identifier (11/29 bit) * bit 29 : error message frame flag (0 = data frame, 1 = error message) * bit 30 : remote transmission request flag (1 = rtr frame) * bit 31 : frame format flag (0 = standard 11 bit, 1 = extended 29 bit) */ 0-28位为标识符,如果是扩展帧,则高11位为标准ID 29位标识是数据帧还是错误消息 30位说明是否是远程帧 31位说明是标准帧还是扩展帧。 以下是在处理can_frame时用到的掩码和标识符: /* special address description flags for the CAN_ID */ #define CAN_EFF_FLAG 0x80000000U /* EFF/SFF is set in the MSB */ #define CAN_RTR_FLAG 0x40000000U /* remote transmission request */ #define CAN_ERR_FLAG 0x20000000U /* error message frame */ /* valid bits in CAN ID for frame formats */ #define CAN_SFF_MASK 0x000007FFU /* standard frame format (SFF) */ #define CAN_EFF_MASK 0x1FFFFFFFU /* extended frame format (EFF) */ #define CAN_ERR_MASK 0x1FFFFFFFU /* omit EFF, RTR, ERR flags */ 对can_frame的处理是在mcp251x_hw_tx中进行的,如下: static void mcp251x_hw_tx(struct spi_device *spi, struct can_frame *frame, int tx_buf_idx) { struct mcp251x_priv *priv = spi_get_drvdata(spi); u32 sid, eid, exide, rtr; u8 buf[SPI_TRANSFER_BUF_LEN]; exide = (frame->can_id & CAN_EFF_FLAG) ? 1 : 0; //取can_id的31位,判断是标准帧还是扩展帧 if (exide) sid = (frame->can_id & CAN_EFF_MASK) >> 18;//如果是扩展帧,can_id的0-28位为ID,其中高11位为标准ID else sid = frame->can_id & CAN_SFF_MASK; /* Standard ID */ eid = frame->can_id & CAN_EFF_MASK; /* Extended ID */ rtr = (frame->can_id & CAN_RTR_FLAG) ? 1 : 0; /* 是否是远程帧*/ buf[TXBCTRL_OFF] = INSTRUCTION_LOAD_TXB(tx_buf_idx); //发送缓冲器控制寄存器地址 buf[TXBSIDH_OFF] = sid >> SIDH_SHIFT; //发送缓冲器标准ID高8位 //5-7位存放发送缓冲器低3位,3位存放帧格式,0-1位存放扩展标识符低18位的高两位(16-17) buf[TXBSIDL_OFF] = ((sid & SIDL_SID_MASK) SIDL_EID_SHIFT) & SIDL_EID_MASK); buf[TXBEID8_OFF] = GET_BYTE(eid, 1); //存放扩展标识符低18位的8-15位 buf[TXBEID0_OFF] = GET_BYTE(eid, 0); //扩展标识符低18位的低8位(0-7) buf[TXBDLC_OFF] = (rtr can_dlc; //6位存放远程帧标识符,0-3存放数据长度码 memcpy(buf + TXBDAT_OFF, frame->data, frame->can_dlc);//拷贝要发送的数据 mcp251x_hw_tx_frame(spi, buf, frame->can_dlc, tx_buf_idx); /* use INSTRUCTION_RTS, to avoid "repeated frame problem" */ priv->spi_tx_buf[0] = INSTRUCTION_RTS(1 spi, 1); } static void mcp251x_hw_rx_frame(struct spi_device *spi, u8 *buf, int buf_idx) { struct mcp251x_priv *priv = spi_get_drvdata(spi); if (mcp251x_is_2510(spi)) { int i, len; for (i = 1; i < RXBDAT_OFF; i++) buf[i] = mcp251x_read_reg(spi, RXBCTRL(buf_idx) + i); len = get_can_dlc(buf[RXBDLC_OFF] & RXBDLC_LEN_MASK); for (; i < (RXBDAT_OFF + len); i++) buf[i] = mcp251x_read_reg(spi, RXBCTRL(buf_idx) + i); } else { priv->spi_tx_buf[RXBCTRL_OFF] = INSTRUCTION_READ_RXB(buf_idx); mcp251x_spi_trans(spi, SPI_TRANSFER_BUF_LEN); memcpy(buf, priv->spi_rx_buf, SPI_TRANSFER_BUF_LEN); } } --------------------- 作者:qwaszx523 来源:CSDN 原文:https://blog.csdn.net/qwaszx523/article/details/54984544 版权声明:本文为博主原创文章,转载请附上博文链接! |
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