在实际项目应用中，如果想利用低成本的mcu来实现BACnet IO模块，可以采用STM32 RS485队列FIFO实现
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>
#include "hardware.h"
#include "bacnet/basic/sys/mstimer.h"
#include "bacnet/bits.h"
#include "bacnet/basic/sys/fifo.h"
#include "led.h"
#include "rs485.h"
/* buffer for storing received bytes - size must be power of two */
static uint8_t Receive_Buffer_Data[512];
static FIFO_BUFFER Receive_Buffer;
/* amount of silence on the wire */
static struct mstimer Silence_Timer;
/* baud rate */
static uint32_t Baud_Rate = 38400;
/* The minimum time after the end of the stop bit of the final octet of a */
/* received frame before a node may enable its EIA-485 driver: 40 bit times. */
/* At 9600 baud, 40 bit times would be about 4.166 milliseconds */
/* At 19200 baud, 40 bit times would be about 2.083 milliseconds */
/* At 38400 baud, 40 bit times would be about 1.041 milliseconds */
/* At 57600 baud, 40 bit times would be about 0.694 milliseconds */
/* At 76800 baud, 40 bit times would be about 0.520 milliseconds */
/* At 115200 baud, 40 bit times would be about 0.347 milliseconds */
/* 40 bits is 4 octets including a start and stop bit with each octet */
#define Tturnaround (40UL)
/*************************************************************************
* Description: Reset the silence on the wire timer.
* Returns: nothing
* Notes: none
**************************************************************************/
void rs485_silence_reset(void)
{
mstimer_set(&Silence_Timer, 0);
}
/*************************************************************************
* Description: Determine the amount of silence on the wire from the timer.
* Returns: true if the amount of time has elapsed
* Notes: none
**************************************************************************/
bool rs485_silence_elapsed(uint32_t interval)
{
return (mstimer_elapsed(&Silence_Timer) > interval);
}
/*************************************************************************
* Description: Baud rate determines turnaround time.
* Returns: amount of milliseconds
* Notes: none
**************************************************************************/
static uint16_t rs485_turnaround_time(void)
{
/* delay after reception before transmitting - per MS/TP spec */
/* wait a minimum 40 bit times since reception */
/* at least 2 ms for errors: rounding, clock tick */
if (Baud_Rate) {
return (2