Interrupt-drive software uart

millwood0 · 发表于 2013-8-18 06:55:07

I wrote a software uart for STM32F10x chips here: http://www.amobbs.com/thread-5542383-1-1.html. On a 24Mhz CM3, it is good up to about 50Kbps, without any optimization.

I mentioned that porting it to the code to other mcus should be fairly easy. Here are two examples of porting that piece of code to a PIC (16F684) and a 89C51.

First, porting it to a 16F684. 16F chips don't have vectored interrupts so it is more involved. But here it is:

//==============uartxisr.h========================
#ifndef _UARTXISR_H
#define _UARTXISR_H
//#include "stm32f10x_rcc.h" //we use rcc
//#include "stm32f10x_tim.h" //we use timer
//hardware configuration
//softuart pin definitions
#define UART_PORT PORTC
#define UART_DDR TRISC
#define UART_TX (1<<2) //tx pin
#define UART_SET(tx) IO_SET(UART_PORT, tx)
#define UART_CLR(tx) IO_CLR(UART_PORT, tx)
//pick the timer to be used
//#define UART_TIM TIM3
#define tmrx_init tmr1_init
#define tmrx_act tmr1_act
#include "tmr1.h" //we use timer
//end hardware configuration
//insert into the isr
#define UARTX_TX_ISR() \
if (TMR1IF) { \
TMR1H = tmr1_offset>>8; \
TMR1L = tmr1_offset/* & 0x00ff*/; \
TMR1IF = 0; \
_tmr1_isr_ptr(); \
}
//uartx protocol
//1 start bit
//8 data bits
//1 stop bit
//lsb first
#define UART_SR(dat) (0x0200 | ((dat) << 1) | 0x0000) //form the uart shift register. 1 start bit (low), 8 data bits, 1 stop bit (high), lsb first
//global defines
//define baud rates
#define UART_BR_300 300ul //baudrate=300 - it overflows under 24Mhz F_CPU
#define UART_BR_600 600ul //baudrate=600
#define UART_BR_1200 1200ul //baudrate=1200
#define UART_BR_2400 2400ul //baudrate=2400
#define UART_BR_4800 4800ul //baudrate=4800
#define UART_BR_9600 9600ul //baudrate=9600
#define UART_BR_19200 19200ul //baudrate=19200
#define UART_BR_38400 38400ul //baudrate=38400
#define UART_BR_57600 57600ul //baudrate=57600 - upper limit for 24Mhz F_CPU
#define UART_BR_115200 115200ul //baudrate=115200
//global variables
//softuart_isr handler
//install this in the timer
void uartx_isr(void);
//reset softuart_isr
void uartx_init(unsigned long baud);
//transmit a string
void uartx_puts(unsigned char * str);
//if uart is busy, return 1
unsigned char uartx_busy(void);
#endif

复制代码

We are using timer1 to generate the baud rate and PORTC.2 as the tx pin.

//================uartxisr.c==========================
#include <htc.h> //we use picc
//#include <stm32f10x.h>
//#include "stm32f10x_gpio.h"
//#include "stm32f10x_tim.h" //we use timer
#include "gpio.h" //we use own macros
#include "tmr1.h" //we use tmr1 as baud rate generator
#include "uartxisr.h" //we use software uart
//hardware configuration
//end hardware configuration
//global defines
//global variables
static unsigned char *_UxTX_ptr;
static unsigned char _UxTX_BUSY=0; //0=u1 transmission done, 1=u1 transmission in process
static unsigned short _UxTX_MASK=0; //current bit being transmitted. 0=end of transmission for the current char
static unsigned short _UxTX_buffer; //software shift register for the transmiter
unsigned short _Ux_OFFSET; //timer offset for uart baud rate
//softuart_isr handler
//install this in the timer
void uartx_isr(void) {
//IO_FLP(UART_PORT, UART_TX); //flip the pin - for debugging
if (_UxTX_MASK!=0x0400) { //current char isn't fully transmitted
if (_UxTX_MASK & _UxTX_buffer) UART_SET(UART_TX); //send '1'
else UART_CLR(UART_TX); //send '0'
_UxTX_MASK = _UxTX_MASK << 1; //shift to the next bit
} else { //current char has been fully transmitted
if (*_UxTX_ptr) { //current char is not a null char
_UxTX_ptr+=1; //increment to the next character
_UxTX_MASK = 0x0001; //1 start bit, 8 data bits, 1 stop bits = 10 bits
_UxTX_buffer = UART_SR(*_UxTX_ptr); //form the buffer to be transmitted
} else { //current char is a null char -> end of transmission
_UxTX_BUSY = 0; //uartx no longer busy
/* TIM IT enable */
//TIM_ITConfig(UART_TIM, TIM_IT_Update, DISABLE); //don't start the isr yet
TMR1IE = 0; //disable tmr1 interrupt
}
}
}
//reset softuart_isr
void uartx_init(unsigned long baud) {
//set up the pin
IO_SET(UART_PORT, UART_TX); //tx idles high
IO_OUT(UART_DDR, UART_TX); //tx as output
//set up the baud rate generator
tmrx_init(0, F_CPU / baud); //set up timer
tmrx_act(uartx_isr); //install the handler
//clear the bits
//TIM_ClearITPendingBit(UART_TIM, TIM_IT_Update);
TMR1IF = 0;
/* TIM IT enable */
//TIM_ITConfig(UART_TIM, TIM_IT_Update, DISABLE); //don't start the isr yet
TMR1IE = 1;
_UxTX_BUSY = 0; //uartx not busy
}
//transmit a string
void uartx_puts(unsigned char * str) {
_UxTX_BUSY = 1; //uartx is busy
_UxTX_ptr = str;
_UxTX_MASK = 0x0001; //1 start bit, 8 data bits, 1 stop bits = 10 bits
_UxTX_buffer = UART_SR(*_UxTX_ptr); //form the buffer to be transmitted
//clear the bits
//TIM_ClearITPendingBit(UART_TIM, TIM_IT_Update);
TMR1IF = 1; //force loading of offsets in the isr
/* TIM IT enable */
//TIM_ITConfig(UART_TIM, TIM_IT_Update, ENABLE); //enable the transmission
TMR1IE = 1;
}
//if uart is busy, return 1
unsigned char uartx_busy(void) {
return _UxTX_BUSY;
}

复制代码

Three routines are involved: uartx_init() initialize the module and sets the baud rate; uartx_puts() sends a string, and uartx_busy() tests if the uartx module is busy.

You can see great similarity between this code base and the one for STM32F.

here is the application code:

//==============main.c===================
#include <htc.h> //we use picc
#include "config.h" //configuration words
#include "gpio.h"
#include "delay.h" //we use software delays
#include "tmr1.h" //we use timer1 for uartxisr
#include "uartxisr.h" //we use software uart isr
//hardware configuration
#define LED_PORT PORTC
#define LED_DDR TRISC
#define LED (1<<0)
#define LED_DLY 100 //delay, in ms
//end hardware configuration
//global defines
//global variables
unsigned char uRAM[]="16F684 UARTXISR...\n\r"; //test string to be sent
//isr
void interrupt isr(void) {
UARTX_TX_ISR(); //uartx transmitter isr
}
//reset the mcu
void mcu_init(void) {
ANSEL = 0x00; //all pins digital
CMCON0= 0x07; //comparators off
IO_CLR(LED_PORT, LED); //clear led
IO_OUT(LED_DDR, LED); //led as output
}
int main(void) {
mcu_init(); //initialize the mcu
uartx_init(UART_BR_1200); //set the baud rate
ei(); //enable interrupt
while (1) {
if (!uartx_busy()) { //uart is not busy
uartx_puts(uRAM); //send the string
}
IO_FLP(LED_PORT, LED); //flip led
//delay_ms(LED_DLY); //waste some time
}
}

复制代码

It is fairly simple: sets up the uart to send a string at 1200bps, and then flip a pin (PORTC.0).

Here is the output:

ronic · 发表于 2013-8-18 08:52:46

good， i raise you

millwood0 · 发表于 2013-8-18 08:52:49

本帖最后由 millwood0 于 2013-8-18 08:53 编辑

Now, on to 89C51. It is actually a lot easier as the chip has a vectored interrupt controller.

#ifndef _UARTXISR_H
#define _UARTXISR_H
//#include "stm32f10x_rcc.h" //we use rcc
//#include "stm32f10x_tim.h" //we use timer
//hardware configuration
//softuart pin definitions
#define UART_PORT P2
#define UART_DDR P2
#define UART_TX (1<<2) //tx pin
#define UART_SET(tx) IO_SET(UART_PORT, tx)
#define UART_CLR(tx) IO_CLR(UART_PORT, tx)
//pick the timer to be used
//#define UART_TIM TIM3
#define tmrx_init tmr1_init
#define tmrx_act tmr1_act
#include "tmr1.h" //we use timer
//end hardware configuration
//insert into the isr
#define UARTX_TX_ISR() \
//if (TMR1IF) { \
TMR1H = tmr1_offset>>8; \
TMR1L = tmr1_offset/* & 0x00ff*/; \
// TMR1IF = 0; \
// _tmr1_isr_ptr(); \
//}
//uartx protocol
//1 start bit
//8 data bits
//1 stop bit
//lsb first
#define UART_SR(dat) (0x0200 | ((dat) << 1) | 0x0000) //form the uart shift register. 1 start bit (low), 8 data bits, 1 stop bit (high), lsb first
//global defines
//define baud rates
#define UART_BR_300 300ul //baudrate=300 - it overflows under 24Mhz F_CPU
#define UART_BR_600 600ul //baudrate=600
#define UART_BR_1200 1200ul //baudrate=1200
#define UART_BR_2400 2400ul //baudrate=2400
#define UART_BR_4800 4800ul //baudrate=4800
#define UART_BR_9600 9600ul //baudrate=9600
#define UART_BR_19200 19200ul //baudrate=19200
#define UART_BR_38400 38400ul //baudrate=38400
#define UART_BR_57600 57600ul //baudrate=57600 - upper limit for 24Mhz F_CPU
#define UART_BR_115200 115200ul //baudrate=115200
//global variables
//softuart_isr handler
//install this in the timer
void uartx_isr(void);
//reset softuart_isr
void uartx_init(unsigned long baud);
//transmit a string
void uartx_puts(unsigned char * str);
//if uart is busy, return 1
unsigned char uartx_busy(void);
#endif

复制代码

the corresponding .c file

//===============uartxisr.c===================
//#include <htc.h> //we use picc
#include <regx51.h> //we use keil c51
//#include <stm32f10x.h>
//#include "stm32f10x_gpio.h"
//#include "stm32f10x_tim.h" //we use timer
#include "gpio.h" //we use own macros
#include "tmr1.h" //we use tmr1 as baud rate generator
#include "uartxisr.h" //we use software uart
//hardware configuration
//end hardware configuration
//global defines
//global variables
static unsigned char *_UxTX_ptr;
static unsigned char _UxTX_BUSY=0; //0=u1 transmission done, 1=u1 transmission in process
static unsigned short _UxTX_MASK=0; //current bit being transmitted. 0=end of transmission for the current char
static unsigned short _UxTX_buffer; //software shift register for the transmiter
unsigned short _Ux_OFFSET; //timer offset for uart baud rate
//softuart_isr handler
//install this in the timer
void uartx_isr(void) {
//IO_FLP(UART_PORT, UART_TX); //flip the pin - for debugging
//load the offset
UARTX_TX_ISR(); //realod the offset
if (_UxTX_MASK!=0x0400) { //current char isn't fully transmitted
if (_UxTX_MASK & _UxTX_buffer) UART_SET(UART_TX); //send '1'
else UART_CLR(UART_TX); //send '0'
_UxTX_MASK = _UxTX_MASK << 1; //shift to the next bit
} else { //current char has been fully transmitted
if (*_UxTX_ptr) { //current char is not a null char
_UxTX_ptr+=1; //increment to the next character
_UxTX_MASK = 0x0001; //1 start bit, 8 data bits, 1 stop bits = 10 bits
_UxTX_buffer = UART_SR(*_UxTX_ptr); //form the buffer to be transmitted
} else { //current char is a null char -> end of transmission
_UxTX_BUSY = 0; //uartx no longer busy
/* TIM IT enable */
//TIM_ITConfig(UART_TIM, TIM_IT_Update, DISABLE); //don't start the isr yet
//TMR1IE = 0; //disable tmr1 interrupt
ET1 = 0; //turn off tmr1 interrupt
}
}
}
//reset softuart_isr
void uartx_init(unsigned long baud) {
//set up the pin
IO_SET(UART_PORT, UART_TX); //tx idles high
IO_OUT(UART_DDR, UART_TX); //tx as output
//set up the baud rate generator
tmrx_init(0, F_CPU / baud); //set up timer
tmrx_act(uartx_isr); //install the handler
//clear the bits
//TIM_ClearITPendingBit(UART_TIM, TIM_IT_Update);
//TMR1IF = 0;
TF1 = 0;
/* TIM IT enable */
//TIM_ITConfig(UART_TIM, TIM_IT_Update, DISABLE); //don't start the isr yet
//TMR1IE = 1;
ET1 = 1;
_UxTX_BUSY = 0; //uartx not busy
}
//transmit a string
void uartx_puts(unsigned char * str) {
_UxTX_BUSY = 1; //uartx is busy
_UxTX_ptr = str;
_UxTX_MASK = 0x0001; //1 start bit, 8 data bits, 1 stop bits = 10 bits
_UxTX_buffer = UART_SR(*_UxTX_ptr); //form the buffer to be transmitted
//clear the bits
//TIM_ClearITPendingBit(UART_TIM, TIM_IT_Update);
//TMR1IF = 1; //force loading of offsets in the isr
TF1 = 1;
/* TIM IT enable */
//TIM_ITConfig(UART_TIM, TIM_IT_Update, ENABLE); //enable the transmission
//TMR1IE = 1;
ET1 = 1;
}
//if uart is busy, return 1
unsigned char uartx_busy(void) {
return _UxTX_BUSY;
}

复制代码

The calling convention is the same:

//==============main.c=================
#include <regx51.h> //we use keil c51
#include "gpio.h"
#include "delay.h" //we use software delay
#include "tmr1.h" //we use timer
#include "uartxisr.h" //we use software uartx
//hardware configuration
#define LED_PORT P2
#define LED_DDR P2
#define LED (1<<0)
#define LED_DLY 100
//end hardware configuration
//global defines
//global variables
unsigned char uRAM[]="89C51 UARTX_ISR...\n\r";
void mcu_init(void) {
IO_CLR(LED_PORT, LED); //clear led
IO_OUT(LED_DDR, LED); //led as output
}
int main(void) {
mcu_init(); //reset the mcu
uartx_init(UART_BR_1200); //set the baud rate
ei(); //enable interrupt
while (1) {
if (!uartx_busy()) { //uartx is not busy
uartx_puts(uRAM); //send the string
}
IO_FLP(LED_PORT, LED); //flip led
//delay_ms(LED_DLY); //waste some time
}
}

复制代码

The output:

Interrupt-drive software uart

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