Changed Tturnaround time in MS/TP modules to be a minimum of 2ms, or use a dummy transmit of 4 bytes while the transceiver is disabled. 1ms delay will always give smaller than 1ms of delay due to silence timer tick.

bacnet-stack/ports/at91sam7s/rs485.c

@@ -167,7 +167,7 @@ void RS485_Turnaround_Delay(
     /* delay after reception before trasmitting - per MS/TP spec */
     /* wait a minimum  40 bit times since reception */
     /* at least 1 ms for errors: rounding, clock tick */
-    turnaround_time = 1 + ((Tturnaround * 1000UL) / RS485_Baud);
+    turnaround_time = 2 + ((Tturnaround * 1000UL) / RS485_Baud);
     while (Timer_Silence() < turnaround_time) {
         /* do nothing - wait for timer to increment */
     };
@@ -241,7 +241,7 @@ bool RS485_ReceiveError(
 }
 
 /****************************************************************************
-* DESCRIPTION: Return true if data is available 
+* DESCRIPTION: Return true if data is available
 * RETURN:      true if data is available, with the data in the parameter set
 * ALGORITHM:   none
 * NOTES:       none

bacnet-stack/ports/atmega168/rs485.c

@@ -44,18 +44,6 @@ static uint8_t LED3_Off_Timer;
 /* baud rate */
 static uint32_t RS485_Baud = 9600;
 
-/* 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)
-/* turnaround_time_milliseconds = (Tturnaround*1000UL)/RS485_Baud; */
-
 /****************************************************************************
 * DESCRIPTION: Initializes the RS485 hardware and variables, and starts in
 *              receive mode.
@@ -137,26 +125,6 @@ bool RS485_Set_Baud_Rate(
     return valid;
 }
 
-/****************************************************************************
-* DESCRIPTION: Waits on the SilenceTimer for 40 bits.
-* RETURN:      none
-* ALGORITHM:   none
-* NOTES:       none
-*****************************************************************************/
-void RS485_Turnaround_Delay(
-    void)
-{
-    uint16_t turnaround_time;
-
-    /* delay after reception before trasmitting - per MS/TP spec */
-    /* wait a minimum  40 bit times since reception */
-    /* at least 1 ms for errors: rounding, clock tick */
-    turnaround_time = 1 + ((Tturnaround * 1000UL) / RS485_Baud);
-    while (Timer_Silence() < turnaround_time) {
-        /* do nothing - wait for timer to increment */
-    };
-}
-
 /****************************************************************************
 * DESCRIPTION: Enable or disable the transmitter
 * RETURN:      none
@@ -173,6 +141,35 @@ void RS485_Transmitter_Enable(
     }
 }
 
+/****************************************************************************
+* DESCRIPTION: Waits on the SilenceTimer for 40 bits.
+* RETURN:      none
+* ALGORITHM:   none
+* NOTES:       none
+*****************************************************************************/
+void RS485_Turnaround_Delay(
+    void)
+{
+    uint8_t nbytes = 4;
+
+    RS485_Transmitter_Enable(false);
+    while (nbytes) {
+        while (!BIT_CHECK(UCSR0A, UDRE0)) {
+            /* do nothing - wait until Tx buffer is empty */
+        }
+        /* Send the data byte */
+        UDR0 = 0xff;
+        nbytes--;
+    }
+    /* was the frame sent? */
+    while (!BIT_CHECK(UCSR0A, TXC0)) {
+        /* do nothing - wait until the entire frame in the
+           Transmit Shift Register has been shifted out */
+    }
+    /* Clear the Transmit Complete flag by writing a one to it. */
+    BIT_SET(UCSR0A, TXC0);
+}
+
 /****************************************************************************
 * DESCRIPTION: Timers for delaying the LED indicators going off
 * RETURN:      none
@@ -253,7 +250,6 @@ void RS485_Send_Data(
     Timer_Silence_Reset();
 }
 
-
 /****************************************************************************
 * DESCRIPTION: Return true if a framing or overrun error is present
 * RETURN:      true if error

bacnet-stack/ports/atmega8/rs485.c

@@ -161,15 +161,24 @@ bool RS485_Set_Baud_Rate(
 void RS485_Turnaround_Delay(
     void)
 {
-    uint16_t turnaround_time;
+    uint8_t nbytes = 4;
 
-    /* delay after reception before trasmitting - per MS/TP spec */
+    RS485_Transmitter_Enable(false);
-    /* wait a minimum  40 bit times since reception */
+    while (nbytes) {
-    /* at least 1 ms for errors: rounding, clock tick */
+        while (!BIT_CHECK(UCSR0A, UDRE0)) {
-    turnaround_time = 1 + ((Tturnaround * 1000UL) / RS485_Baud);
+            /* do nothing - wait until Tx buffer is empty */
-    while (!timer_silence_elapsed(turnaround_time)) {
+        }
-        /* do nothing - wait for timer to increment */
+        /* Send the data byte */
-    };
+        UDR0 = 0xff;
+        nbytes--;
+    }
+    /* was the frame sent? */
+    while (!BIT_CHECK(UCSR0A, TXC0)) {
+        /* do nothing - wait until the entire frame in the
+           Transmit Shift Register has been shifted out */
+    }
+    /* Clear the Transmit Complete flag by writing a one to it. */
+    BIT_SET(UCSR0A, TXC0);
 }
 
 /****************************************************************************

bacnet-stack/ports/bdk-atxx4-mstp/rs485.c

@@ -94,15 +94,26 @@ static void rs485_receiver_enable(
 void rs485_turnaround_delay(
     void)
 {
-    uint16_t turnaround_time;
+    uint8_t nbytes = 4;
 
     /* delay after reception before trasmitting - per MS/TP spec */
-    /* wait a minimum  40 bit times since reception */
+    /*  Transmit 4 dummy bytes with RS485 driver off.
-    /* at least 1 ms for errors: rounding, clock tick */
+        This equals the 40 bit times (1 start, 8 data, 1 stop). */
-    turnaround_time = 1 + ((Tturnaround * 1000UL) / Baud_Rate);
+    rs485_rts_enable(false);
-    while (!timer_elapsed_milliseconds_short(&Silence_Timer, turnaround_time)) {
+    while (nbytes) {
-        /* do nothing - wait for timer to increment */
+        /* Send the data byte */
-    };
+        UDR0 = 0xff;
+        while (!BIT_CHECK(UCSR0A, UDRE0)) {
+            /* do nothing - wait until Tx buffer is empty */
+        }
+        nbytes--;
+    }
+    while (!BIT_CHECK(UCSR0A, TXC0)) {
+        /* do nothing - wait until the entire frame in the
+           Transmit Shift Register has been shifted out */
+    }
+    /* Clear the Transmit Complete flag by writing a one to it. */
+    BIT_SET(UCSR0A, TXC0);
 }
 
 ISR(USART0_RX_vect)

bacnet-stack/ports/linux/rs485.c

@@ -184,7 +184,7 @@ void RS485_Send_Frame(
         else if (baud == 19200)
             turnaround_time = 2;
         else
-            turnaround_time = 1;
+            turnaround_time = 2;
         while (mstp_port->SilenceTimer() < turnaround_time) {
             /* do nothing - wait for timer to increment */
             sched_yield();

bacnet-stack/ports/pic18f6720/rs485.c

@@ -78,7 +78,7 @@ void RS485_Send_Frame(
     else if (RS485_Baud_Rate == 19200)
         turnaround_time = 2;
     else
-        turnaround_time = 1;
+        turnaround_time = 2;
 
     while (mstp_port->SilenceTimer < turnaround_time) {
         /* The line has not been silent long enough, so wait. */

bacnet-stack/ports/rtos32/rs485.c

@@ -172,6 +172,7 @@ void RS485_Send_Frame(
 {       /* number of bytes of data (up to 501) */
     bool status = true; /* return value */
 
+    /* fixme: wait turnaround time */
     RS485_TRANSMIT_ENABLE(RS485_Port);
     SendBlock(RS485_Port, (char *) buffer, nbytes);
     /* need to wait at least 9600 baud * 512 bytes = 54mS */
@@ -179,8 +180,8 @@ void RS485_Send_Frame(
     while (!(LineStatus(RS485_Port) & TX_SHIFT_EMPTY))
         RTKScheduler();
     RS485_RECEIVE_ENABLE(RS485_Port);
-    /* SilenceTimer is cleared by the Receive State Machine when 
+    /* SilenceTimer is cleared by the Receive State Machine when
-       activity is detected and by the SendFrame procedure as each 
+       activity is detected and by the SendFrame procedure as each
        octet is transmitted. */
     mstp_port->SilenceTimer = 0;
 #if PRINT_ENABLED_RS485

bacnet-stack/ports/win32/rs485.c

@@ -383,7 +383,7 @@ void RS485_Send_Frame(
         else if (baud == 19200)
             turnaround_time = 2;
         else
-            turnaround_time = 1;
+            turnaround_time = 2;
         while (mstp_port->SilenceTimer() < turnaround_time) {
             /* do nothing - wait for timer to increment */
         };