BACnet协议栈移植分析之一:rs485.c
从现在开始分析BACnet协议栈了，版本号是bacnet-stack-0.7.1。目录是bacnet-stack-0.7.1\ports\linux\rs485.c
rs485.c文件主要要解决在物理层发送和接收数据的作用。不同的开发板需要移植该文件。
#include <errno.h>
#include <stddef.h>
#include <stdint.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* Linux includes */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <unistd.h>
#include <sched.h>
/* Local includes */
#include "mstp.h"
#include "rs485.h"
#include "fifo.h"
#include <sys/select.h>
#include <sys/time.h>
/* Posix serial programming reference:
http://www.easysw.com/~mike/serial/serial.html */
/* Use ionice wrapper to improve serial performance:
$ sudo ionice -c 1 -n 0 ./bin/bacserv 12345
*/
/* handle returned from open() */
static int RS485_Handle = -1;
/* baudrate settings are defined in <asm/termbits.h>, which is
included by <termios.h> */
static unsigned int RS485_Baud = B38400;//波特率选择38400 bps
/* serial port name, /dev/ttyS0,
/dev/ttyUSB0 for USB->RS485 from B&B Electronics USOPTL4 */
static char *RS485_Port_Name = "/dev/ttyUSB0"; /*系统默认是通过USB转485的，根据需要设置，若你的开发板用485接口，则用static char *RS485_Port_Name = "/dev/ttyS0";代替 */
/* some terminal I/O have RS-485 specific functionality */
#ifndef RS485MOD
#define RS485MOD 0
#endif
/* serial I/O settings */
static struct termios RS485_oldtio;
/* Ring buffer for incoming bytes, in order to speed up the receiving. */
static FIFO_BUFFER Rx_FIFO;
/* buffer size needs to be a power of 2 */
static uint8_t Rx_Buffer[4096];
#define _POSIX_SOURCE 1 /* POSIX compliant source */
/*********************************************************************
* DESCRIPTION: Configures the interface name
* RETURN: none
* ALGORITHM: none
* NOTES: none
*********************************************************************/
void RS485_Set_Interface(
char *ifname)
{
/* note: expects a constant char, or char from the heap */
if (ifname) {
RS485_Port_Name = ifname;
}
}
/*********************************************************************
* DESCRIPTION: Returns the interface name
* RETURN: none
* ALGORITHM: none
* NOTES: none
*********************************************************************/
const char *RS485_Interface(
void)
{
return RS485_Port_Name;
}
/****************************************************************************
* DESCRIPTION: Returns the baud rate that we are currently running at
* RETURN: none
* ALGORITHM: none
* NOTES: none
*****************************************************************************/
uint32_t RS485_Get_Baud_Rate(
void)
{
uint32_t baud = 0;
switch (RS485_Baud) {
case B0:
baud = 0;
break;
case B50:
baud = 50;
break;
case B75:
baud = 75;
break;
case B110:
baud = 110;
break;
case B134:
baud = 134;
break;
case B150:
baud = 150;
break;
case B200:
baud = 200;
break;
case B300:
baud = 300;
break;
case B600:
baud = 600;
break;
case B1200:
baud = 1200;
break;
case B1800:
baud = 1800;
break;
case B2400:
baud = 2400;
break;
case B4800:
baud = 4800;
break;
case B9600:
baud = 9600;
break;
case B19200:
baud = 19200;
break;
case B38400:
baud = 38400;
break;
case B57600:
baud = 57600;
break;
case B115200:
baud = 115200;
break;
case B230400:
baud = 230400;
break;
default:
baud = 9600;
}
return baud;
}
/****************************************************************************
* DESCRIPTION: Sets the baud rate for the chip USART
* RETURN: none
* ALGORITHM: none
* NOTES: none
*****************************************************************************/
bool RS485_Set_Baud_Rate(
uint32_t baud)
{
bool valid = true;
switch (baud) {
case 0:
RS485_Baud = B0;
break;
case 50:
RS485_Baud = B50;
break;
case 75:
RS485_Baud = B75;
break;
case 110:
RS485_Baud = B110;
break;
case 134:
RS485_Baud = B134;
break;
case 150:
RS485_Baud = B150;
break;
case 200:
RS485_Baud = B200;
break;
case 300:
RS485_Baud = B300;
break;
case 600:
RS485_Baud = B600;
break;
case 1200:
RS485_Baud = B1200;
break;
case 1800:
RS485_Baud = B1800;
break;
case 2400:
RS485_Baud = B2400;
break;
case 4800:
RS485_Baud = B4800;
break;
case 9600:
RS485_Baud = B9600;
break;
case 19200:
RS485_Baud = B19200;
break;
case 38400:
RS485_Baud = B38400;
break;
case 57600:
RS485_Baud = B57600;
break;
case 115200:
RS485_Baud = B115200;
break;
case 230400:
RS485_Baud = B230400;
break;
default:
valid = false;
break;
}
if (valid) {
/* FIXME: store the baud rate */
}
return valid;
}
/****************************************************************************
* DESCRIPTION: Transmit a frame on the wire
* RETURN: none
* ALGORITHM: none
* NOTES: none
*****************************************************************************/
void RS485_Send_Frame(
volatile struct mstp_port_struct_t *mstp_port, /* port specific data */
uint8_t * buffer, /* frame to send (up to 501 bytes of data) */
uint16_t nbytes)
{ /* number of bytes of data (up to 501) */
uint32_t turnaround_time = Tturnaround * 1000;
uint32_t baud = RS485_Get_Baud_Rate();
ssize_t written = 0;
int greska;
/* sleeping for turnaround time is necessary to give other devices
time to change from sending to receiving state. */
usleep(turnaround_time / baud); //至少要等待Tturnaround时间才启动RS485缓冲器发送
/*
On success, the number of bytes written are returned (zero indicates
nothing was written). On error, -1 is returned, and errno is set
appropriately. If count is zero and the file descriptor refers to a
regular file, 0 will be returned without causing any other effect. For
a special file, the results are not portable.
*/
written = write(RS485_Handle, buffer, nbytes); //RS485_Handle初始时是为-1，当发出open操作时应该是个正整数，而write函数的原型是(fd,buf,n)
greska = errno;
if (written <= 0) {
printf("write error: %s\n", strerror(greska));
} else {
/* wait until all output has been transmitted. */
tcdrain(RS485_Handle); //Linux中的传输等待函数
}
/* tcdrain(RS485_Handle); */
/* per MSTP spec, sort of */
if (mstp_port) {
mstp_port->SilenceTimerReset();
}
return;
}
/****************************************************************************
* DESCRIPTION: Get a byte of receive data
* RETURN: none
* ALGORITHM: none
* NOTES: none
*****************************************************************************/
RS485_Check_UART_Data函数分别检查ReceiveError、DataAvailable。然后选择端口从UART中读数据
void RS485_Check_UART_Data(
volatile struct mstp_port_struct_t *mstp_port)
{
fd_set input;
struct timeval waiter;
uint8_t buf[2048];
int n;
if (mstp_port->ReceiveError == true) {
/* do nothing but wait for state machine to clear the error */
/* burning time, so wait a longer time */
waiter.tv_sec = 0;
waiter.tv_usec = 5000;
} else if (mstp_port->DataAvailable == false) {
/* wait for state machine to read from the DataRegister */
if (FIFO_Count(&Rx_FIFO) > 0) {
/* data is available */
mstp_port->DataRegister = FIFO_Get(&Rx_FIFO);
mstp_port->DataAvailable = true;
/* FIFO is giving data - don't wait very long */
waiter.tv_sec = 0;
waiter.tv_usec = 10;
} else {
/* FIFO is empty - wait a longer time */
waiter.tv_sec = 0;
waiter.tv_usec = 5000;
}
}
/* grab bytes and stuff them into the FIFO every time */
FD_ZERO(&input);
FD_SET(RS485_Handle, &input);
n = select(RS485_Handle + 1, &input, NULL, NULL, &waiter);
if (n < 0) {
return;
}
if (FD_ISSET(RS485_Handle, &input)) {
n = read(RS485_Handle, buf, sizeof(buf));
FIFO_Add(&Rx_FIFO, &buf[0], n);
}
}
void RS485_Cleanup(
void)
{
/* restore the old port settings */
tcsetattr(RS485_Handle, TCSANOW, &RS485_oldtio); //tcgetattr用于获取终端的相关参数，而tcsetattr函数用于设置终端参数
close(RS485_Handle);
}
void RS485_Initialize(
void)
{
struct termios newtio;
printf("RS485: Initializing %s", RS485_Port_Name);
/*
Open device for reading and writing.
Blocking mode - more CPU effecient
*/
RS485_Handle = open(RS485_Port_Name, O_RDWR | O_NOCTTY /*| O_NDELAY */ );
if (RS485_Handle < 0) {
perror(RS485_Port_Name);
exit(-1);
}
#if 0
/* non blocking for the read */
fcntl(RS485_Handle, F_SETFL, FNDELAY);
#else
/* efficient blocking for the read */
fcntl(RS485_Handle, F_SETFL, 0);
#endif
/* save current serial port settings */
tcgetattr(RS485_Handle, &RS485_oldtio);
/* clear struct for new port settings */
bzero(&newtio, sizeof(newtio));
/*
BAUDRATE: Set bps rate. You could also use cfsetispeed and cfsetospeed.
CRTSCTS : output hardware flow control (only used if the cable has
all necessary lines. See sect. 7 of Serial-HOWTO)
CS8 : 8n1 (8bit,no parity,1 stopbit)
CLOCAL : local connection, no modem contol
CREAD : enable receiving characters
*/
newtio.c_cflag = RS485_Baud | CS8 | CLOCAL | CREAD | RS485MOD;
/* Raw input */
newtio.c_iflag = 0;
/* Raw output */
newtio.c_oflag = 0;
/* no processing */
newtio.c_lflag = 0;
/* activate the settings for the port after flushing I/O */
tcsetattr(RS485_Handle, TCSAFLUSH, &newtio);
/* destructor */
atexit(RS485_Cleanup);
/* flush any data waiting */
usleep(200000);
tcflush(RS485_Handle, TCIOFLUSH);
/* ringbuffer */
FIFO_Init(&Rx_FIFO, Rx_Buffer, sizeof(Rx_Buffer));
printf("=success!\n");
}
/*以上都是为了兼容POSIX接口而编写的，Linux系统中最关键的是一下代码*/
#ifdef TEST_RS485
#include <string.h>
int main(
int argc,
char *argv[])
{
uint8_t buf[8];
char *wbuf = { "BACnet!" };
size_t wlen = strlen(wbuf) + 1;
unsigned i = 0;
size_t written = 0;
int rlen;
/*设置串口，如波特率，端口，初始化*/
/* argv has the "/dev/ttyS0" or some other device */
if (argc > 1) {
RS485_Set_Interface(argv[1]);
}
RS485_Set_Baud_Rate(38400);
RS485_Initialize();
/*循环读取串口的数据*/
for (;;) {
written = write(RS485_Handle, wbuf, wlen);
rlen = read(RS485_Handle, buf, sizeof(buf));
/* print any characters received */
if (rlen > 0) {
for (i = 0; i < rlen; i++) {
fprintf(stderr, "%02X ", buf[i]); //长度不足2的话前面补0
}
}
}
return 0;
}
#endif
补充：
1、select函数用于在非阻塞中，当一个套接字或一组套接字有信号时通知你，系统提供select函数来实现多路复用输入/输出模型，原型：
#include <sys/time.h>
#include <unistd.h>
int select(int maxfd,fd_set *rdset,fd_set *wrset,fd_set *exset,struct timeval *timeout);
参数maxfd是需要监视的最大的文件描述符值+1；rdset,wrset,exset分别对应于需要检测的可读文件描述符的集合，可写文件描述符的集 合及异常文件描述符的集合。struct timeval结构用于描述一段时间长度，如果在这个时间内，需要监视的描述符没有事件发生则函数返回，返回值为0。
fd_set（它比较重要所以先介绍一下）是一组文件描述字(fd)的集合，它用一位来表示一个fd（下面会仔细介绍），对于fd_set类型通过下面四个宏来操作：
FD_ZERO(fd_set *fdset);将指定的文件描述符集清空，在对文件描述符集合进行设置前，必须对其进行初始化，如果不清空，由于在系统分配内存空间后，通常并不作清空处理，所以结果是不可知的。
FD_SET(int fd, fd_set *fdset);用于在文件描述符集合中增加一个新的文件描述符。
FD_CLR(int fd, fd_set *fdset);用于在文件描述符集合中删除一个文件描述符。
FD_ISSET(int fd, fd_set *fdset);用于测试指定的文件描述符是否在该集合中。
过去，一个fd_set通常只能包含<32的fd（文件描述字），因为fd_set其实只用了一个32位矢量来表示fd；现在,UNIX系统通常会在头文件<sys/select.h>中定义常量FD_SETSIZE，它是数据类型fd_set的描述字数量，其值通常是1024，这样就能表示<1024的fd。根据fd_set的位矢量实现，我们可以重新理解操作fd_set的四个宏：
fd_set set;
FD_ZERO(&set);
FD_SET(0, &set);
FD_CLR(4, &set);
FD_ISSET(5, &set);
―――――――――――――――――――――――――――――――――――――――
注意fd的最大值必须<FD_SETSIZE。
2、struct termios结构体
一、数据成员
tcflag_t c_iflag; /* 输入模式 */
tcflag_t c_oflag; /* 输出模式 */
tcflag_t c_cflag; /* 控制模式 */
tcflag_t c_lflag; /* 本地模式 */
cc_t c_cc[NCCS]; /* 控制字符 */