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Improve timing to make LESS blocking #14

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Improve timing to make LESS blocking #14

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39a7c9f
Improve LCD library to become less blocking
techpaul Feb 9, 2016
afa9c4a
LCD Library 4 bit improvements
techpaul Feb 11, 2016
9073940
Add method to extend Command Delay beyond default 40us to max of 200us
techpaul Feb 11, 2016
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144 changes: 92 additions & 52 deletions src/LiquidCrystal.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5,20 +5,24 @@
#include <inttypes.h>
#include "Arduino.h"

// Minimum time between falling edges of E (enable pin to do writes)
#define _LCD_COMMAND_DELAY 40
#define _MAX_COMMAND_DELAY 200

// When the display powers up, it is configured as follows:
//
// 1. Display clear
// 2. Function set:
// DL = 1; 8-bit interface data
// N = 0; 1-line display
// F = 0; 5x8 dot character font
// 3. Display on/off control:
// D = 0; Display off
// C = 0; Cursor off
// B = 0; Blinking off
// 4. Entry mode set:
// I/D = 1; Increment by 1
// S = 0; No shift
// 2. Function set:
// DL = 1; 8-bit interface data
// N = 0; 1-line display
// F = 0; 5x8 dot character font
// 3. Display on/off control:
// D = 0; Display off
// C = 0; Cursor off
// B = 0; Blinking off
// 4. Entry mode set:
// I/D = 1; Increment by 1
// S = 0; No shift
//
// Note, however, that resetting the Arduino doesn't reset the LCD, so we
// can't assume that its in that state when a sketch starts (and the
Expand Down Expand Up @@ -57,22 +61,22 @@ void LiquidCrystal::init(uint8_t fourbitmode, uint8_t rs, uint8_t rw, uint8_t en
_rs_pin = rs;
_rw_pin = rw;
_enable_pin = enable;

_data_pins[0] = d0;
_data_pins[1] = d1;
_data_pins[2] = d2;
_data_pins[3] = d3;
_data_pins[3] = d3;
_data_pins[4] = d4;
_data_pins[5] = d5;
_data_pins[6] = d6;
_data_pins[7] = d7;
_data_pins[7] = d7;

if (fourbitmode)
_displayfunction = LCD_4BITMODE | LCD_1LINE | LCD_5x8DOTS;
else
else
_displayfunction = LCD_8BITMODE | LCD_1LINE | LCD_5x8DOTS;

begin(16, 1);
_comm_delay = _LCD_COMMAND_DELAY; // Default command delay
begin(16, 1);
}

void LiquidCrystal::begin(uint8_t cols, uint8_t lines, uint8_t dotsize) {
Expand All @@ -81,7 +85,7 @@ void LiquidCrystal::begin(uint8_t cols, uint8_t lines, uint8_t dotsize) {
}
_numlines = lines;

setRowOffsets(0x00, 0x40, 0x00 + cols, 0x40 + cols);
setRowOffsets(0x00, 0x40, 0x00 + cols, 0x40 + cols);

// for some 1 line displays you can select a 10 pixel high font
if ((dotsize != LCD_5x8DOTS) && (lines == 1)) {
Expand All @@ -90,47 +94,47 @@ void LiquidCrystal::begin(uint8_t cols, uint8_t lines, uint8_t dotsize) {

pinMode(_rs_pin, OUTPUT);
// we can save 1 pin by not using RW. Indicate by passing 255 instead of pin#
if (_rw_pin != 255) {
if (_rw_pin != 255) {
pinMode(_rw_pin, OUTPUT);
}
pinMode(_enable_pin, OUTPUT);

// Do these once, instead of every time a character is drawn for speed reasons.
for (int i=0; i<((_displayfunction & LCD_8BITMODE) ? 8 : 4); ++i)
{
pinMode(_data_pins[i], OUTPUT);
}
}

// SEE PAGE 45/46 FOR INITIALIZATION SPECIFICATION!
// according to datasheet, we need at least 40ms after power rises above 2.7V
// before sending commands. Arduino can turn on way before 4.5V so we'll wait 50
delayMicroseconds(50000);
delayMicroseconds(50000);
// Now we pull both RS and R/W low to begin commands
digitalWrite(_rs_pin, LOW);
digitalWrite(_enable_pin, LOW);
if (_rw_pin != 255) {
if (_rw_pin != 255) {
digitalWrite(_rw_pin, LOW);
}

//put the LCD into 4 bit or 8 bit mode
if (! (_displayfunction & LCD_8BITMODE)) {
// this is according to the hitachi HD44780 datasheet
// figure 24, pg 46

// we start in 8bit mode, try to set 4 bit mode
write4bits(0x03);
writebits(0x03, 4, 1);
delayMicroseconds(4500); // wait min 4.1ms

// second try
write4bits(0x03);
writebits(0x03, 4, 1);
delayMicroseconds(4500); // wait min 4.1ms

// third go!
write4bits(0x03);
writebits(0x03, 4, 1);
delayMicroseconds(150);

// finally, set to 4-bit interface
write4bits(0x02);
writebits(0x02, 4, 1);
} else {
// this is according to the hitachi HD44780 datasheet
// page 45 figure 23
Expand All @@ -148,10 +152,10 @@ void LiquidCrystal::begin(uint8_t cols, uint8_t lines, uint8_t dotsize) {
}

// finally, set # lines, font size, etc.
command(LCD_FUNCTIONSET | _displayfunction);
command(LCD_FUNCTIONSET | _displayfunction);

// turn the display on with no cursor or blinking default
_displaycontrol = LCD_DISPLAYON | LCD_CURSOROFF | LCD_BLINKOFF;
_displaycontrol = LCD_DISPLAYON | LCD_CURSOROFF | LCD_BLINKOFF;
display();

// clear it off
Expand Down Expand Up @@ -194,7 +198,7 @@ void LiquidCrystal::setCursor(uint8_t col, uint8_t row)
if ( row >= _numlines ) {
row = _numlines - 1; // we count rows starting w/0
}

command(LCD_SETDDRAMADDR | (col + _row_offsets[row]));
}

Expand Down Expand Up @@ -260,6 +264,7 @@ void LiquidCrystal::noAutoscroll(void) {
command(LCD_ENTRYMODESET | _displaymode);
}


// Allows us to fill the first 8 CGRAM locations
// with custom characters
void LiquidCrystal::createChar(uint8_t location, uint8_t charmap[]) {
Expand All @@ -270,6 +275,24 @@ void LiquidCrystal::createChar(uint8_t location, uint8_t charmap[]) {
}
}


/* New method that if default command delay is not long enough
to set a new value between
_LCD_COMMAND_DELAY (default 40 us)
_MAX_COMMAND_DELAY (default 200 us)

Should be called before you call begin method

returns 0 for success
-1 for error (invalid parameter)
*/
int LiquidCrystal::setCommandDelay( uint8_t delay ) {
if( delay >= _LCD_COMMAND_DELAY && delay <= _MAX_COMMAND_DELAY ) {
_comm_delay = delay;
return 0;
}
return -1;
}
/*********** mid level commands, for sending data/cmds */

inline void LiquidCrystal::command(uint8_t value) {
Expand All @@ -288,39 +311,56 @@ void LiquidCrystal::send(uint8_t value, uint8_t mode) {
digitalWrite(_rs_pin, mode);

// if there is a RW pin indicated, set it low to Write
if (_rw_pin != 255) {
if (_rw_pin != 255) {
digitalWrite(_rw_pin, LOW);
}

if (_displayfunction & LCD_8BITMODE) {
write8bits(value);
writebits(value, 8, 0);
} else {
write4bits(value>>4);
write4bits(value);
writebits(value>>4, 4, 0);
writebits(value, 4, 1);
}
}

void LiquidCrystal::pulseEnable(void) {
digitalWrite(_enable_pin, LOW);
delayMicroseconds(1);

/* pulseEnable once data and RS set pulse enable line to send data in 4/8 bit mode

Checks when last falling edge of enable was and if sending a NEW command
delays for time to get up to _comm_delay to ensure controller ready

When in 4 bit mode 2nd nibble can be sent at minimum delay for Enable high
time delay 1us

Parameter type - 0 = new command start
1 = 2nd nibble for 4 bit mode (needs 1us delay
NOT _comm_delay)
*/
void LiquidCrystal::pulseEnable(uint8_t type) {
unsigned long _delaymicros;

digitalWrite(_enable_pin, HIGH);
delayMicroseconds(1); // enable pulse must be >450ns
_delaymicros = micros( ) - _oldmicros; // PREVIOUS commands need > 37us to settle
if( _delaymicros < _comm_delay && type == 0 )
delayMicroseconds( _comm_delay - _delaymicros ); // wait time for delay
else
delayMicroseconds(1); // enable pulse HIGH must be >450ns
digitalWrite(_enable_pin, LOW);
delayMicroseconds(100); // commands need > 37us to settle
_oldmicros = micros( ); // save time to check next time
}

void LiquidCrystal::write4bits(uint8_t value) {
for (int i = 0; i < 4; i++) {
digitalWrite(_data_pins[i], (value >> i) & 0x01);
}

pulseEnable();
}
/* writebits transfer correct number of bits to output and then call pulse enable

void LiquidCrystal::write8bits(uint8_t value) {
for (int i = 0; i < 8; i++) {
Parameters value - 4 or 8 bits to send
in 4 bit mode shift top 4 bits right before calling
bits - value 4 or 8 for bits to send
type - 0 = new command start
1 = 2nd nibble for 4 bit mode (needs 1us delay NOT _MIN_WRITE_DELAY
*/
void LiquidCrystal::writebits(uint8_t value, uint8_t bits, uint8_t type) {
for (int i = 0; i < bits; i++) {
digitalWrite(_data_pins[i], (value >> i) & 0x01);
}

pulseEnable();
pulseEnable( type );
}
14 changes: 8 additions & 6 deletions src/LiquidCrystal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -58,7 +58,7 @@ class LiquidCrystal : public Print {
void init(uint8_t fourbitmode, uint8_t rs, uint8_t rw, uint8_t enable,
uint8_t d0, uint8_t d1, uint8_t d2, uint8_t d3,
uint8_t d4, uint8_t d5, uint8_t d6, uint8_t d7);

void begin(uint8_t cols, uint8_t rows, uint8_t charsize = LCD_5x8DOTS);

void clear();
Expand All @@ -76,24 +76,25 @@ class LiquidCrystal : public Print {
void rightToLeft();
void autoscroll();
void noAutoscroll();
int setCommandDelay( uint8_t );

void setRowOffsets(int row1, int row2, int row3, int row4);
void createChar(uint8_t, uint8_t[]);
void setCursor(uint8_t, uint8_t);
void setCursor(uint8_t, uint8_t);
virtual size_t write(uint8_t);
void command(uint8_t);

using Print::write;
private:
void send(uint8_t, uint8_t);
void write4bits(uint8_t);
void write8bits(uint8_t);
void pulseEnable();
void writebits(uint8_t, uint8_t, uint8_t);
void pulseEnable( uint8_t );

uint8_t _rs_pin; // LOW: command. HIGH: character.
uint8_t _rw_pin; // LOW: write to LCD. HIGH: read from LCD.
uint8_t _enable_pin; // activated by a HIGH pulse.
uint8_t _data_pins[8];
uint8_t _comm_delay; // Delay between commands by default _LCD_COMMAND_DELAY

uint8_t _displayfunction;
uint8_t _displaycontrol;
Expand All @@ -103,6 +104,7 @@ class LiquidCrystal : public Print {

uint8_t _numlines;
uint8_t _row_offsets[4];
unsigned long _oldmicros;
};

#endif