Diff: soft_uart.cpp

Revision:

5:46a732673cc5

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/soft_uart.cpp	Sat Mar 26 09:26:26 2022 +0000
@@ -0,0 +1,256 @@
+// UART.C
+//
+// Generic software uart written in C, requiring a timer set to 3 times
+// the baud rate, and two software read/write pins for the receive and
+// transmit functions.
+//
+// * Received characters are buffered
+// * putchar(), getchar(), kbhit() and flush_input_buffer() are available
+// * There is a facility for background processing while waiting for input
+//
+// Colin Gittins, Software Engineer, Halliburton Energy Services
+//
+// The baud rate can be configured by changing the BAUD_RATE macro as
+// follows:
+//
+// #define BAUD_RATE            19200.0
+//
+// The function init_uart() must be called before any comms can take place
+//
+// Interface routines required:
+// 1. get_rx_pin_status()
+//    Returns 0 or 1 dependent on whether the receive pin is high or low.
+// 2. set_tx_pin_high()
+//    Sets the transmit pin to the high state.
+// 3. set_tx_pin_low()
+//    Sets the transmit pin to the low state.
+// 4. idle()
+//    Background functions to execute while waiting for input.
+// 5. timer_set( BAUD_RATE )
+//    Sets the timer to 3 times the baud rate.
+// 6. set_timer_interrupt( timer_isr )
+//    Enables the timer interrupt.
+//
+// Functions provided:
+// 1. void flush_input_buffer( void )
+//    Clears the contents of the input buffer.
+// 2. char kbhit( void )
+//    Tests whether an input character has been received.
+// 3. char getchar( void )
+//    Reads a character from the input buffer, waiting if necessary.
+// 4. void turn_rx_on( void )
+//    Turns on the receive function.
+// 5. void turn_rx_off( void )
+//    Turns off the receive function.
+// 6. void putchar( char )
+//    Writes a character to the serial port.
+#include "mbed.h"
+#include <stdio.h>
+ 
+#define BAUD_RATE       9600
+#define IN_BUF_SIZE     256
+ 
+#define TRUE 1
+#define FALSE 0
+ 
+static unsigned char        inbuf[IN_BUF_SIZE];
+static unsigned char        qin = 0;
+static unsigned char        qout = 0;
+ 
+static char             flag_rx_waiting_for_stop_bit;
+static char             flag_rx_off;
+static char             rx_mask;
+static char             flag_rx_ready;
+static char             flag_tx_ready;
+static char             timer_rx_ctr;
+static char             timer_tx_ctr;
+static char             bits_left_in_rx;
+static char             bits_left_in_tx;
+static char             rx_num_of_bits;
+static char             tx_num_of_bits;
+static int              internal_rx_buffer;
+static int              internal_tx_buffer;
+static int              user_tx_buffer;
+ 
+DigitalOut TX(PA_6);
+DigitalIn RX(PA_7);
+Ticker ticker;
+
+//Background functions to execute while waiting for input.
+void idle(){
+    wait_us(0.2);
+}
+ 
+//Sets the transmit pin to the high state.
+void set_tx_pin_high() {
+    TX = 1;
+}
+ 
+//Sets the transmit pin to the low state.
+void set_tx_pin_low() {
+    TX = 0;
+}
+ 
+//Returns 0 or 1 dependent on whether the receive pin is high or low
+int get_rx_pin_status() {
+    return RX.read();
+}
+ 
+void timer_isr(void)
+    {
+    char    mask, start_bit, flag_in;
+
+// Transmitter Section
+    if ( flag_tx_ready )
+        {
+        
+        if ( --timer_tx_ctr<=0 )
+            {
+            mask = internal_tx_buffer&1;
+            internal_tx_buffer >>= 1;
+            if ( mask )
+                {
+                set_tx_pin_high();          
+                }
+            else
+                {
+                set_tx_pin_low();
+                }
+            timer_tx_ctr = 3;
+            if ( --bits_left_in_tx<=0 )
+                {
+                flag_tx_ready = FALSE;
+                }
+            }
+        }
+// Receiver Section
+    if ( flag_rx_off==FALSE )
+        {
+        if ( flag_rx_waiting_for_stop_bit )
+            {
+            if ( --timer_rx_ctr<=0 )
+                {
+                flag_rx_waiting_for_stop_bit = FALSE;
+                flag_rx_ready = FALSE;
+                internal_rx_buffer &= 0xFF;
+                if ( internal_rx_buffer!=0xC2 )
+                    {
+                    inbuf[qin] = internal_rx_buffer;
+                    if ( ++qin>=IN_BUF_SIZE )
+                        {
+                        qin = 0;
+                        }
+                    }
+                }
+            }
+        else        // rx_test_busy
+            {
+            if ( flag_rx_ready==FALSE )
+                {
+                start_bit = get_rx_pin_status();
+// Test for Start Bit
+                if ( start_bit==0 )
+                    {
+                    flag_rx_ready = TRUE;
+                    internal_rx_buffer = 0;
+                    timer_rx_ctr = 4;
+                    bits_left_in_rx = rx_num_of_bits;
+                    rx_mask = 1;
+                    }
+                }
+            else    // rx_busy
+                {
+                if ( --timer_rx_ctr<=0 )
+                    {               // rcv
+                    timer_rx_ctr = 3;
+                    flag_in = get_rx_pin_status();
+                    if ( flag_in )
+                        {
+                        internal_rx_buffer |= rx_mask;
+                        }
+                    rx_mask <<= 1;
+                    if ( --bits_left_in_rx<=0 )
+                        {
+                        flag_rx_waiting_for_stop_bit = TRUE;
+                        }
+                    }
+                }
+            }
+        }
+    }
+ 
+void init_uart( void )
+    {
+    flag_tx_ready = FALSE;
+    flag_rx_ready = FALSE;
+    flag_rx_waiting_for_stop_bit = FALSE;
+    flag_rx_off = FALSE;
+    rx_num_of_bits = 8;//10
+    tx_num_of_bits = 10;//10
+ 
+    set_tx_pin_high();
+    ticker.attach_us(&timer_isr, 1000000.0 / (BAUD_RATE * 3.0));
+ 
+    }
+ 
+char _getchar( void )
+    {
+    char        ch;
+ 
+    do
+        {
+        while ( qout==qin )
+            {
+            idle();
+            }
+        ch = inbuf[qout] & 0xFF;
+        if ( ++qout>=IN_BUF_SIZE )
+            {
+            qout = 0;
+            }
+        }
+    while ( ch==0x0A || ch==0xC2 );
+    return( ch );
+    }
+ 
+void _putchar( int ch )
+    {
+    while ( flag_tx_ready );
+    user_tx_buffer = ch;
+ 
+// invoke_UART_transmit
+    timer_tx_ctr = 3;
+    bits_left_in_tx = tx_num_of_bits;
+    internal_tx_buffer = (user_tx_buffer<<1) | 0x200;;
+    flag_tx_ready = TRUE;
+    }
+ 
+void flush_input_buffer( void )
+    {
+    qin = 0;
+    qout = 0;
+    }
+ 
+char kbhit( void )
+    {
+    return( qin!=qout );
+    }
+ 
+void turn_rx_on( void )
+    {
+    flag_rx_off = FALSE;
+    }
+ 
+void turn_rx_off( void )
+    {
+    flag_rx_off = TRUE;
+    }
+    
+void printStr(char* str){
+    int i = 0;
+    int len = strlen(str); 
+    for(i = 0; i<len; i++){
+     wait(0.01);
+        _putchar(str[i]);
+    }
+}