attiny: add local copy of SoftI2CMaster.h

reform-tiny-fw/SoftI2CMaster.h

@@ -0,0 +1,862 @@
+/* Arduino SoftI2C library. 
+ *
+ * Version 1.4
+ *
+ * Copyright (C) 2013, Bernhard Nebel and Peter Fleury
+ *
+ * This is a very fast and very light-weight software I2C-master library 
+ * written in assembler. It is based on Peter Fleury's I2C software
+ * library: http://homepage.hispeed.ch/peterfleury/avr-software.html
+ * Recently, the hardware implementation has been added to the code,
+ * which can be enabled by defining I2C_HARDWARE.
+ *
+ * This Library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with the Arduino I2cMaster Library.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ */
+
+/* In order to use the library, you need to define SDA_PIN, SCL_PIN,
+ * SDA_PORT and SCL_PORT before including this file.  Have a look at
+ * http://www.arduino.cc/en/Reference/PortManipulation for finding out
+ * which values to use. For example, if you use digital pin 3 (corresponding 
+ * to PD3) for SDA and digital pin 13 (corresponding to PB5)
+ * for SCL on a standard Arduino,
+ * you have to use the following definitions: 
+ * #define SDA_PIN 3 
+ * #define SDA_PORT PORTD
+ * #define SCL_PIN 5
+ * #define SCL_PORT PORTB
+ *
+ * Alternatively, you can define the compile time constant I2C_HARDWARE,
+ * in which case the TWI hardware is used. In this case you have to use
+ * the standard SDA/SCL pins (and, of course, the chip needs to support
+ * this).
+ *
+ * You can also define the following constants (see also below):
+ ' - I2C_PULLUP = 1 meaning that internal pullups should be used 
+ * - I2C_CPUFREQ, when changing CPU clock frequency dynamically
+ * - I2C_FASTMODE = 1 meaning that the I2C bus allows speeds up to 400 kHz
+ * - I2C_SLOWMODE = 1 meaning that the I2C bus will allow only up to 25 kHz 
+ * - I2C_NOINTERRUPT = 1 in order to prohibit interrupts while 
+ *   communicating (see below). This can be useful if you use the library 
+ *   for communicationg with SMbus devices, which have timeouts.
+ *   Note, however, that interrupts are disabled from issuing a start condition
+ *   until issuing a stop condition. So use this option with care!
+ * - I2C_TIMEOUT = 0..10000 msec in order to return from the I2C functions
+ *   in case of a I2C bus lockup (i.e., SCL constantly low). 0 means no timeout.
+ * - I2C_MAXWAIT = 0..32767 number of retries in i2c_start_wait. 0 means never stop.
+ */
+
+/* Changelog:
+ * Version 2.1
+ * - added conditional to check whether it is the right MCU type
+ * Version 2.0
+ * - added hardware support as well.
+ * Version 1.4:
+ * - added "maximum retry" in i2c_start_wait in order to avoid lockup
+ * - added "internal pullups", but be careful since the option stretches the I2C specs
+ * Version 1.3:
+ * - added "__attribute__ ((used))" for all functions declared with "__attribute__ ((noinline))"
+ *   Now the module is also usable in Arduino 1.6.11+
+ * Version 1.2:
+ * - added pragma to avoid "unused parameter warnings" (suggestion by Walter)
+ * - replaced wrong license file
+ * Version 1.1: 
+ * - removed I2C_CLOCK_STRETCHING
+ * - added I2C_TIMEOUT time in msec (0..10000) until timeout or 0 if no timeout
+ * - changed i2c_init to return true iff both SDA and SCL are high
+ * - changed interrupt disabling so that the previous IRQ state is restored
+ * Version 1.0: basic functionality
+ */
+
+#ifndef __AVR_ARCH__
+#error "Not an AVR MCU! Use 'SlowSoftI2CMaster' library instead of 'SoftI2CMaster'!"
+#else
+
+#ifndef _SOFTI2C_H
+#define _SOFTI2C_H   1
+
+#include <avr/io.h>
+#include <Arduino.h>
+#include <util/twi.h>
+
+#pragma GCC diagnostic push
+
+#pragma GCC diagnostic ignored "-Wunused-parameter"
+
+
+
+// Init function. Needs to be called once in the beginning.
+// Returns false if SDA or SCL are low, which probably means 
+// a I2C bus lockup or that the lines are not pulled up.
+bool __attribute__ ((noinline)) i2c_init(void) __attribute__ ((used));
+
+// Start transfer function: <addr> is the 8-bit I2C address (including the R/W
+// bit). 
+// Return: true if the slave replies with an "acknowledge", false otherwise
+bool __attribute__ ((noinline)) i2c_start(uint8_t addr) __attribute__ ((used)); 
+
+// Similar to start function, but wait for an ACK! Will timeout if I2C_MAXWAIT > 0.
+bool  __attribute__ ((noinline)) i2c_start_wait(uint8_t addr) __attribute__ ((used));
+
+// Repeated start function: After having claimed the bus with a start condition,
+// you can address another or the same chip again without an intervening 
+// stop condition.
+// Return: true if the slave replies with an "acknowledge", false otherwise
+bool __attribute__ ((noinline)) i2c_rep_start(uint8_t addr) __attribute__ ((used));
+
+// Issue a stop condition, freeing the bus.
+void __attribute__ ((noinline)) i2c_stop(void) asm("ass_i2c_stop") __attribute__ ((used));
+
+// Write one byte to the slave chip that had been addressed
+// by the previous start call. <value> is the byte to be sent.
+// Return: true if the slave replies with an "acknowledge", false otherwise
+bool __attribute__ ((noinline)) i2c_write(uint8_t value) asm("ass_i2c_write") __attribute__ ((used));
+
+
+// Read one byte. If <last> is true, we send a NAK after having received 
+// the byte in order to terminate the read sequence. 
+uint8_t __attribute__ ((noinline)) i2c_read(bool last) __attribute__ ((used));
+
+// If you want to use the TWI hardeware, you have to define I2C_HARDWARE to be 1
+#ifndef I2C_HARDWARE
+#define I2C_HARDWARE 0
+#endif
+
+#if I2C_HARDWARE
+#ifndef TWDR
+#error This chip does not support hardware I2C. Please undfine I2C_HARDWARE
+#endif
+#endif
+
+// You can set I2C_CPUFREQ independently of F_CPU if you 
+// change the CPU frequency on the fly. If you do not define it,
+// it will use the value of F_CPU
+#ifndef I2C_CPUFREQ
+#define I2C_CPUFREQ F_CPU
+#endif
+
+// If I2C_FASTMODE is set to 1, then the highest possible frequency below 400kHz
+// is selected. Be aware that not all slave chips may be able to deal with that!
+#ifndef I2C_FASTMODE
+#define I2C_FASTMODE 0
+#endif
+
+// If I2C_FASTMODE is not defined or defined to be 0, then you can set
+// I2C_SLOWMODE to 1. In this case, the I2C frequency will not be higher 
+// than 25KHz. This could be useful for problematic buses with high pull-ups
+// and high capasitance.
+#ifndef I2C_SLOWMODE
+#define I2C_SLOWMODE 0
+#endif
+
+// If I2C_PULLUP is set to 1, then the internal pull-up resistors are used.
+// This does not conform with the I2C specs, since the bus lines will be
+// temporarily in high-state and the internal resistors have roughly 50k.
+// With low bus speeds und short buses it usually works, though (hopefully).
+#ifndef I2C_PULLUP
+#define I2C_PULLUP 0
+#endif
+
+// if I2C_NOINTERRUPT is 1, then the I2C routines are not interruptable.
+// This is most probably only necessary if you are using a 1MHz system clock,
+// you are communicating with a SMBus device, and you want to avoid timeouts.
+// Be aware that the interrupt bit is enabled after each call. So the
+// I2C functions should not be called in interrupt routines or critical regions.
+#ifndef I2C_NOINTERRUPT
+#define I2C_NOINTERRUPT 0
+#endif
+
+// I2C_TIMEOUT can be set to a value between 1 and 10000.
+// If it is defined and nonzero, it leads to a timeout if the
+// SCL is low longer than I2C_TIMEOUT milliseconds, i.e., max timeout is 10 sec
+#ifndef I2C_TIMEOUT
+#define I2C_TIMEOUT 0
+#else 
+#if I2C_TIMEOUT > 10000
+#error I2C_TIMEOUT is too large
+#endif
+#endif
+
+// I2C_MAXWAIT can be set to any value between 0 and 32767. 0 means no time out.
+#ifndef I2C_MAXWAIT
+#define I2C_MAXWAIT 500
+#else
+#if I2C_MAXWAIT > 32767 || I2C_MAXWAIT < 0
+#error Illegal I2C_MAXWAIT value
+#endif
+#endif
+
+#define I2C_TIMEOUT_DELAY_LOOPS (I2C_CPUFREQ/1000UL)*I2C_TIMEOUT/4000UL
+#if I2C_TIMEOUT_DELAY_LOOPS < 1
+#define I2C_MAX_STRETCH 1
+#else
+#if I2C_TIMEOUT_DELAY_LOOPS > 60000UL
+#define I2C_MAX_STRETCH 60000UL
+#else
+#define I2C_MAX_STRETCH I2C_TIMEOUT_DELAY_LOOPS
+#endif
+#endif
+
+#if I2C_FASTMODE
+#define I2C_DELAY_COUNTER (((I2C_CPUFREQ/350000L)/2-18)/3)
+#define SCL_CLOCK 400000UL
+#else
+#if I2C_SLOWMODE
+#define I2C_DELAY_COUNTER (((I2C_CPUFREQ/23500L)/2-18)/3)
+#define SCL_CLOCK 25000UL
+#else
+#define I2C_DELAY_COUNTER (((I2C_CPUFREQ/90000L)/2-18)/3)
+#define SCL_CLOCK 100000UL
+#endif
+#endif
+
+// constants for reading & writing
+#define I2C_READ    1
+#define I2C_WRITE   0
+
+#if !I2C_HARDWARE
+// map the IO register back into the IO address space
+#define SDA_DDR       	(_SFR_IO_ADDR(SDA_PORT) - 1)
+#define SCL_DDR       	(_SFR_IO_ADDR(SCL_PORT) - 1)
+#define SDA_OUT       	_SFR_IO_ADDR(SDA_PORT)
+#define SCL_OUT       	_SFR_IO_ADDR(SCL_PORT)
+#define SDA_IN		(_SFR_IO_ADDR(SDA_PORT) - 2)
+#define SCL_IN		(_SFR_IO_ADDR(SCL_PORT) - 2)
+
+#ifndef __tmp_reg__
+#define __tmp_reg__ 0
+#endif
+ 
+// Internal delay functions.
+void __attribute__ ((noinline)) i2c_delay_half(void) asm("ass_i2c_delay_half")  __attribute__ ((used));
+void __attribute__ ((noinline)) i2c_wait_scl_high(void) asm("ass_i2c_wait_scl_high")  __attribute__ ((used));
+
+void  i2c_delay_half(void)
+{ // function call 3 cycles => 3C
+#if I2C_DELAY_COUNTER < 1
+  __asm__ __volatile__ (" ret");
+  // 7 cycles for call and return
+#else
+  __asm__ __volatile__ 
+    (
+     " ldi      r25, %[DELAY]           ;load delay constant   ;; 4C \n\t"
+     "_Lidelay: \n\t"
+     " dec r25                          ;decrement counter     ;; 4C+xC \n\t"
+     " brne _Lidelay                                           ;;5C+(x-1)2C+xC\n\t"
+     " ret                                                     ;; 9C+(x-1)2C+xC = 7C+xC" 
+     : : [DELAY] "M" I2C_DELAY_COUNTER : "r25");
+  // 7 cycles + 3 times x cycles
+#endif
+}
+
+void i2c_wait_scl_high(void)
+{
+#if I2C_TIMEOUT <= 0
+  __asm__ __volatile__ 
+    ("_Li2c_wait_stretch: \n\t"
+     " sbis	%[SCLIN],%[SCLPIN]	;wait for SCL high \n\t" 
+     " rjmp	_Li2c_wait_stretch \n\t"
+     " cln                              ;signal: no timeout \n\t"
+     " ret "
+     : : [SCLIN] "I" (SCL_IN), [SCLPIN] "I" (SCL_PIN));
+#else
+  __asm__ __volatile__ 
+    ( " ldi     r27, %[HISTRETCH]       ;load delay counter \n\t"
+      " ldi     r26, %[LOSTRETCH] \n\t"
+      "_Lwait_stretch: \n\t"
+      " clr     __tmp_reg__             ;do next loop 255 times \n\t"
+      "_Lwait_stretch_inner_loop: \n\t"
+      " rcall   _Lcheck_scl_level       ;call check function   ;; 12C \n\t"
+      " brpl    _Lstretch_done          ;done if N=0           ;; +1 = 13C\n\t"
+      " dec     __tmp_reg__             ;dec inner loop counter;; +1 = 14C\n\t"
+      " brne    _Lwait_stretch_inner_loop                      ;; +2 = 16C\n\t"
+      " sbiw    r26,1                   ;dec outer loop counter \n\t"
+      " brne    _Lwait_stretch          ;continue with outer loop \n\t"
+      " sen                             ;timeout -> set N-bit=1 \n\t"
+      " rjmp _Lwait_return              ;and return with N=1\n\t"
+      "_Lstretch_done:                  ;SCL=1 sensed \n\t"            
+      " cln                             ;OK -> clear N-bit \n\t"
+      " rjmp _Lwait_return              ; and return with N=0 \n\t"
+
+      "_Lcheck_scl_level:                                      ;; call = 3C\n\t"
+      " cln                                                    ;; +1C = 4C \n\t"
+      " sbic	%[SCLIN],%[SCLPIN]      ;skip if SCL still low ;; +2C = 6C \n\t"
+      " rjmp    _Lscl_high                                     ;; +0C = 6C \n\t"
+      " sen                                                    ;; +1 = 7C\n\t "
+      "_Lscl_high: "
+      " nop                                                    ;; +1C = 8C \n\t"
+      " ret                             ;return N-Bit=1 if low ;; +4 = 12C\n\t"
+
+      "_Lwait_return:"
+      : : [SCLIN] "I" (SCL_IN), [SCLPIN] "I" (SCL_PIN), 
+	[HISTRETCH] "M" (I2C_MAX_STRETCH>>8), 
+	[LOSTRETCH] "M" (I2C_MAX_STRETCH&0xFF)
+      : "r26", "r27");
+#endif
+}
+#endif // !I2C_HARDWARE
+
+bool i2c_init(void)
+#if I2C_HARDWARE
+{
+#if I2C_PULLUP
+  digitalWrite(SDA, 1);
+  digitalWrite(SCL, 1);
+#else
+  digitalWrite(SDA, 0);
+  digitalWrite(SCL, 0);
+#endif
+#if ((I2C_CPUFREQ/SCL_CLOCK)-16)/2 < 250
+  TWSR = 0;                         /* no prescaler */
+  TWBR = ((I2C_CPUFREQ/SCL_CLOCK)-16)/2;  /* must be > 10 for stable operation */
+#else
+  TWSR = (1<<TWPS0); // prescaler is 4
+  TWBR = ((I2C_CPUFREQ/SCL_CLOCK)-16)/8;
+#endif
+  return (digitalRead(SDA) != 0 && digitalRead(SCL) != 0);
+}
+#else
+{
+  __asm__ __volatile__ 
+    (" cbi      %[SDADDR],%[SDAPIN]     ;release SDA \n\t" 
+     " cbi      %[SCLDDR],%[SCLPIN]     ;release SCL \n\t" 
+#if I2C_PULLUP
+     " sbi      %[SDAOUT],%[SDAPIN]     ;enable SDA pull-up\n\t"
+#else
+     " cbi      %[SDAOUT],%[SDAPIN]     ;clear SDA output value \n\t"     
+#endif
+#if I2C_PULLUP
+     " sbi      %[SCLOUT],%[SCLPIN]     ;enable SCL pull-up\n\t"
+#else
+     " cbi      %[SCLOUT],%[SCLPIN]     ;clear SCL output value \n\t"
+#endif
+     " clr      r24                     ;set return value to false \n\t"
+     " clr      r25                     ;set return value to false \n\t"
+     " sbis     %[SDAIN],%[SDAPIN]      ;check for SDA high\n\t"
+     " ret                              ;if low return with false \n\t"  
+     " sbis     %[SCLIN],%[SCLPIN]      ;check for SCL high \n\t"
+     " ret                              ;if low return with false \n\t" 
+     " ldi      r24,1                   ;set return value to true \n\t"
+     " ret "
+     : :
+       [SCLDDR] "I"  (SCL_DDR), [SCLPIN] "I" (SCL_PIN), 
+       [SCLIN] "I" (SCL_IN), [SCLOUT] "I" (SCL_OUT),
+       [SDADDR] "I"  (SDA_DDR), [SDAPIN] "I" (SDA_PIN), 
+       [SDAIN] "I" (SDA_IN), [SDAOUT] "I" (SDA_OUT)); 
+  return true;
+}
+#endif
+
+bool  i2c_start(uint8_t addr)
+#if I2C_HARDWARE
+{
+  uint8_t   twst;
+#if I2C_TIMEOUT
+  uint32_t start = millis();
+#endif
+
+  // send START condition
+  TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
+
+  // wait until transmission completed
+  while(!(TWCR & (1<<TWINT))) {
+#if I2C_TIMEOUT
+    if (millis() - start > I2C_TIMEOUT) return false;
+#endif
+  }
+
+  // check value of TWI Status Register. Mask prescaler bits.
+  twst = TW_STATUS & 0xF8;
+  if ( (twst != TW_START) && (twst != TW_REP_START)) return false;
+  
+  // send device address
+  TWDR = addr;
+  TWCR = (1<<TWINT) | (1<<TWEN);
+  
+  // wail until transmission completed and ACK/NACK has been received
+  while(!(TWCR & (1<<TWINT))) {
+#if I2C_TIMEOUT
+    if (millis() - start > I2C_TIMEOUT) return false;
+#endif
+  }
+  
+  // check value of TWI Status Register. Mask prescaler bits.
+  twst = TW_STATUS & 0xF8;
+  if ( (twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK) ) return false;
+  
+  return true;
+}
+#else
+{
+  __asm__ __volatile__ 
+    (
+#if I2C_NOINTERRUPT
+     " cli                              ;clear IRQ bit \n\t"
+#endif
+     " sbis     %[SCLIN],%[SCLPIN]      ;check for clock stretching slave\n\t"
+     " rcall    ass_i2c_wait_scl_high   ;wait until SCL=H\n\t"
+#if I2C_PULLUP
+     " cbi      %[SDAOUT],%[SDAPIN]     ;disable pull-up \n\t"
+#endif
+     " sbi      %[SDADDR],%[SDAPIN]     ;force SDA low  \n\t" 
+     " rcall    ass_i2c_delay_half      ;wait T/2 \n\t"
+     " rcall    ass_i2c_write           ;now write address \n\t"
+     " ret"
+     : : [SDADDR] "I"  (SDA_DDR), [SDAPIN] "I" (SDA_PIN),
+       [SDAOUT] "I" (SDA_OUT), [SCLOUT] "I" (SCL_OUT),
+       [SCLIN] "I" (SCL_IN),[SCLPIN] "I" (SCL_PIN)); 
+  return true; // we never return here!
+}
+#endif
+
+bool  i2c_rep_start(uint8_t addr)
+#if I2C_HARDWARE
+{
+  return i2c_start(addr);
+}
+#else
+{
+  __asm__ __volatile__ 
+
+    (
+#if I2C_NOINTERRUPT
+     " cli \n\t"
+#endif
+#if I2C_PULLUP
+     " cbi      %[SCLOUT],%[SCLPIN]     ;disable SCL pull-up \n\t"
+#endif
+     " sbi	%[SCLDDR],%[SCLPIN]	;force SCL low \n\t" 
+     " rcall 	ass_i2c_delay_half	;delay  T/2 \n\t" 
+     " cbi	%[SDADDR],%[SDAPIN]	;release SDA \n\t"
+#if I2C_PULLUP
+     " sbi      %[SDAOUT],%[SDAPIN]     ;enable SDA pull-up \n\t"
+#endif
+     " rcall	ass_i2c_delay_half	;delay T/2 \n\t" 
+     " cbi	%[SCLDDR],%[SCLPIN]	;release SCL \n\t"
+#if I2C_PULLUP
+     " sbi      %[SCLOUT],%[SCLPIN]	;enable SCL pull-up \n\t"
+#endif
+     " rcall 	ass_i2c_delay_half	;delay  T/2 \n\t" 
+     " sbis     %[SCLIN],%[SCLPIN]      ;check for clock stretching slave\n\t"
+     " rcall    ass_i2c_wait_scl_high   ;wait until SCL=H\n\t"
+#if I2C_PULLUP
+     " cbi 	%[SDAOUT],%[SDAPIN]	;disable SDA pull-up\n\t"
+#endif
+     " sbi 	%[SDADDR],%[SDAPIN]	;force SDA low \n\t"
+     " rcall 	ass_i2c_delay_half	;delay	T/2 \n\t" 
+     " rcall    ass_i2c_write       \n\t"
+     " ret"
+     : : [SCLDDR] "I"  (SCL_DDR), [SCLPIN] "I" (SCL_PIN),
+       [SCLIN] "I" (SCL_IN), [SCLOUT] "I" (SCL_OUT), [SDAOUT] "I" (SDA_OUT),
+       [SDADDR] "I"  (SDA_DDR), [SDAPIN] "I" (SDA_PIN)); 
+  return true; // just to fool the compiler
+}
+#endif
+
+bool  i2c_start_wait(uint8_t addr)
+#if I2C_HARDWARE
+{
+  uint8_t   twst;
+  uint16_t maxwait = I2C_MAXWAIT;
+#if I2C_TIMEOUT
+  uint32_t start = millis();
+#endif
+  
+  while (true) {
+    // send START condition
+    TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
+    
+    // wait until transmission completed
+    while(!(TWCR & (1<<TWINT))) {
+#if I2C_TIMEOUT
+    if (millis() - start > I2C_TIMEOUT) return false;
+#endif
+    }
+    
+    // check value of TWI Status Register. Mask prescaler bits.
+    twst = TW_STATUS & 0xF8;
+    if ( (twst != TW_START) && (twst != TW_REP_START)) continue;
+    
+    // send device address
+    TWDR = addr;
+    TWCR = (1<<TWINT) | (1<<TWEN);
+    
+    // wail until transmission completed
+    while(!(TWCR & (1<<TWINT))) {
+#if I2C_TIMEOUT
+      if (millis() - start > I2C_TIMEOUT) return false;
+#endif
+    }
+    
+    // check value of TWI Status Register. Mask prescaler bits.
+    twst = TW_STATUS & 0xF8;
+    if ( (twst == TW_MT_SLA_NACK )||(twst ==TW_MR_DATA_NACK) ) 
+      {    	    
+	/* device busy, send stop condition to terminate write operation */
+	TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
+	
+	// wait until stop condition is executed and bus released
+	while(TWCR & (1<<TWSTO)) {
+#if I2C_TIMEOUT
+	  if (millis() - start > I2C_TIMEOUT) return false;
+#endif
+	}
+
+	if (maxwait)
+	  if (--maxwait == 0)
+	    return false;
+	
+	continue;
+      }
+    //if( twst != TW_MT_SLA_ACK) return 1;
+    return true;
+  }
+}
+#else
+{
+ __asm__ __volatile__ 
+   (
+    " push	r24                     ;save original parameter \n\t"
+#if I2C_MAXWAIT
+    " ldi     r31, %[HIMAXWAIT]         ;load max wait counter \n\t"
+    " ldi     r30, %[LOMAXWAIT]         ;load low byte \n\t"
+#endif
+    "_Li2c_start_wait1: \n\t"
+    " pop       r24                     ;restore original parameter\n\t"
+    " push      r24                     ;and save again \n\t"
+#if I2C_NOINTERRUPT
+    " cli                               ;disable interrupts \n\t"
+#endif
+    " sbis     %[SCLIN],%[SCLPIN]      ;check for clock stretching slave\n\t"
+    " rcall    ass_i2c_wait_scl_high   ;wait until SCL=H\n\t" 
+#if I2C_PULLUP
+     " cbi      %[SDAOUT],%[SDAPIN]     ;disable pull-up \n\t"
+#endif
+    " sbi 	%[SDADDR],%[SDAPIN]	;force SDA low \n\t" 
+    " rcall 	ass_i2c_delay_half	;delay T/2 \n\t" 
+    " rcall 	ass_i2c_write	        ;write address \n\t" 
+    " tst	r24		        ;if device not busy -> done \n\t" 
+    " brne	_Li2c_start_wait_done \n\t" 
+    " rcall	ass_i2c_stop	        ;terminate write & enable IRQ \n\t"
+#if I2C_MAXWAIT
+    " sbiw      r30,1                   ;decrement max wait counter\n\t"
+    " breq       _Li2c_start_wait_done  ;if zero reached, exit with false -> r24 already zero!\n\t"
+#endif
+    " rjmp	_Li2c_start_wait1	;device busy, poll ack again \n\t" 
+    "_Li2c_start_wait_done: \n\t"
+    " clr       r25                     ;clear high byte of return value\n\t"
+    " pop       __tmp_reg__             ;pop off orig argument \n\t"
+    " ret "
+    : : [SDADDR] "I"  (SDA_DDR), [SDAPIN] "I" (SDA_PIN), [SDAOUT] "I" (SDA_OUT),
+      [SCLIN] "I" (SCL_IN), [SCLPIN] "I" (SCL_PIN),
+      [HIMAXWAIT] "M" (I2C_MAXWAIT>>8), 
+      [LOMAXWAIT] "M" (I2C_MAXWAIT&0xFF)
+    : "r30", "r31" ); 
+}
+#endif
+
+void  i2c_stop(void)
+#if I2C_HARDWARE
+{
+#if I2C_TIMEOUT
+  uint32_t start = millis();
+#endif
+  /* send stop condition */
+  TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
+  
+  // wait until stop condition is executed and bus released
+  while(TWCR & (1<<TWSTO)) {
+#if I2C_TIMEOUT
+    if (millis() - start > I2C_TIMEOUT) return;
+#endif
+  }
+}
+#else
+{
+  __asm__ __volatile__ 
+    (
+#if I2C_PULLUP
+     " cbi      %[SCLOUT],%[SCLPIN]     ;disable SCL pull-up \n\t"
+#endif
+     " sbi      %[SCLDDR],%[SCLPIN]     ;force SCL low \n\t"
+#if I2C_PULLUP
+     " cbi      %[SDAOUT],%[SDAPIN]     ;disable pull-up \n\t"
+#endif     
+     " sbi      %[SDADDR],%[SDAPIN]     ;force SDA low \n\t" 
+     " rcall    ass_i2c_delay_half      ;T/2 delay \n\t"
+     " cbi      %[SCLDDR],%[SCLPIN]     ;release SCL \n\t" 
+#if I2C_PULLUP
+     " sbi      %[SCLOUT],%[SCLPIN]	;enable SCL pull-up \n\t"
+#endif
+     " rcall    ass_i2c_delay_half      ;T/2 delay \n\t"
+     " sbis     %[SCLIN],%[SCLPIN]      ;check for clock stretching slave\n\t"
+     " rcall    ass_i2c_wait_scl_high   ;wait until SCL=H\n\t" 
+     " cbi      %[SDADDR],%[SDAPIN]     ;release SDA \n\t"
+#if I2C_PULLUP
+     " sbi      %[SDAOUT],%[SDAPIN]     ;enable SDA pull-up \n\t"
+#endif
+     " rcall    ass_i2c_delay_half \n\t"
+#if I2C_NOINTERRUPT
+     " sei                              ;enable interrupts again!\n\t"
+#endif
+     : : [SCLDDR] "I"  (SCL_DDR), [SCLPIN] "I" (SCL_PIN), [SCLIN] "I" (SCL_IN),
+       [SDAOUT] "I" (SDA_OUT), [SCLOUT] "I" (SCL_OUT),
+       [SDADDR] "I"  (SDA_DDR), [SDAPIN] "I" (SDA_PIN)); 
+}
+#endif
+
+
+bool i2c_write(uint8_t value)
+#if I2C_HARDWARE
+{	
+  uint8_t   twst;
+#if I2C_TIMEOUT
+  uint32_t start = millis();
+#endif
+
+    
+  // send data to the previously addressed device
+  TWDR = value;
+  TWCR = (1<<TWINT) | (1<<TWEN);
+  
+  // wait until transmission completed
+  while(!(TWCR & (1<<TWINT))) {
+#if I2C_TIMEOUT
+    if (millis() - start > I2C_TIMEOUT) return false;
+#endif
+  }
+  
+  // check value of TWI Status Register. Mask prescaler bits
+  twst = TW_STATUS & 0xF8;
+  if( twst != TW_MT_DATA_ACK) return false;
+  return true;
+}
+#else
+{
+  __asm__ __volatile__ 
+    (
+     " sec                              ;set carry flag \n\t"
+     " rol      r24                     ;shift in carry and shift out MSB \n\t"
+     " rjmp _Li2c_write_first \n\t"
+     "_Li2c_write_bit:\n\t"
+     " lsl      r24                     ;left shift into carry ;; 1C\n\t"
+     "_Li2c_write_first:\n\t"
+     " breq     _Li2c_get_ack           ;jump if TXreg is empty;; +1 = 2C \n\t"
+#if I2C_PULLUP
+     " cbi      %[SCLOUT],%[SCLPIN]     ;disable SCL pull-up \n\t"
+#endif
+     " sbi      %[SCLDDR],%[SCLPIN]     ;force SCL low         ;; +2 = 4C \n\t"
+     " nop \n\t"
+     " nop \n\t"
+     " nop \n\t"
+     " brcc     _Li2c_write_low                                ;;+1/+2=5/6C\n\t"
+     " nop                                                     ;; +1 = 7C \n\t"
+     " cbi %[SDADDR],%[SDAPIN]	        ;release SDA           ;; +2 = 9C \n\t"
+#if I2C_PULLUP
+     " sbi      %[SDAOUT],%[SDAPIN]     ;enable SDA pull-up \n\t"
+#endif
+     " rjmp      _Li2c_write_high                              ;; +2 = 11C \n\t"
+     "_Li2c_write_low: \n\t"
+#if I2C_PULLUP
+     " cbi      %[SDAOUT],%[SDAPIN]     ;disable pull-up \n\t"
+#endif
+     " sbi	%[SDADDR],%[SDAPIN]	;force SDA low         ;; +2 = 9C \n\t"
+     " rjmp	_Li2c_write_high                               ;;+2 = 11C \n\t"
+     "_Li2c_write_high: \n\t"
+#if I2C_DELAY_COUNTER >= 1
+     " rcall 	ass_i2c_delay_half	;delay T/2             ;;+X = 11C+X\n\t"
+#endif
+     " cbi	%[SCLDDR],%[SCLPIN]	;release SCL           ;;+2 = 13C+X\n\t"
+#if I2C_PULLUP
+     " sbi      %[SCLOUT],%[SCLPIN]	;enable SCL pull-up \n\t"
+#endif
+     " cln                              ;clear N-bit           ;;+1 = 14C+X\n\t"
+     " nop \n\t"
+     " nop \n\t"
+     " nop \n\t"
+     " sbis	%[SCLIN],%[SCLPIN]	;check for SCL high    ;;+2 = 16C+X\n\t"
+     " rcall    ass_i2c_wait_scl_high \n\t"
+     " brpl     _Ldelay_scl_high                              ;;+2 = 18C+X\n\t"
+     "_Li2c_write_return_false: \n\t"
+     " clr      r24                     ; return false because of timeout \n\t"
+     " rjmp     _Li2c_write_return \n\t"
+     "_Ldelay_scl_high: \n\t"
+#if I2C_DELAY_COUNTER >= 1
+     " rcall	ass_i2c_delay_half	;delay T/2             ;;+X= 18C+2X\n\t"
+#endif
+     " rjmp	_Li2c_write_bit \n\t"
+     "              ;; +2 = 20C +2X for one bit-loop \n\t"
+     "_Li2c_get_ack: \n\t"
+#if I2C_PULLUP
+     " cbi      %[SCLOUT],%[SCLPIN]     ;disable SCL pull-up \n\t"
+#endif
+     " sbi	%[SCLDDR],%[SCLPIN]	;force SCL low ;; +2 = 5C \n\t"
+     " nop \n\t"
+     " nop \n\t"
+     " cbi	%[SDADDR],%[SDAPIN]	;release SDA ;;+2 = 7C \n\t"
+#if I2C_PULLUP
+     " sbi      %[SDAOUT],%[SDAPIN]     ;enable SDA pull-up \n\t"
+#endif
+#if I2C_DELAY_COUNTER >= 1
+     " rcall	ass_i2c_delay_half	;delay T/2 ;; +X = 7C+X \n\t"
+#endif
+     " clr	r25                                            ;; 17C+2X \n\t"
+     " clr	r24		        ;return 0              ;; 14C + X \n\t"
+     " cbi	%[SCLDDR],%[SCLPIN]	;release SCL ;; +2 = 9C+X\n\t"
+#if I2C_PULLUP
+     " sbi      %[SCLOUT],%[SCLPIN]	;enable SCL pull-up \n\t"
+#endif
+     "_Li2c_ack_wait: \n\t"
+     " cln                              ; clear N-bit          ;; 10C + X\n\t" 
+     " nop \n\t"
+     " sbis	%[SCLIN],%[SCLPIN]	;wait SCL high         ;; 12C + X \n\t"
+     " rcall    ass_i2c_wait_scl_high \n\t"
+     " brmi     _Li2c_write_return_false                       ;; 13C + X \n\t "
+     " sbis	%[SDAIN],%[SDAPIN]      ;if SDA hi -> return 0 ;; 15C + X \n\t"
+     " ldi	r24,1                   ;return true           ;; 16C + X \n\t"
+#if I2C_DELAY_COUNTER >= 1
+     " rcall	ass_i2c_delay_half	;delay T/2             ;; 16C + 2X \n\t"
+#endif
+     "_Li2c_write_return: \n\t"
+     " nop \n\t "
+     " nop \n\t "
+#if I2C_PULLUP
+     " cbi      %[SCLOUT],%[SCLPIN]     ;disable SCL pull-up \n\t"
+#endif
+     " sbi	%[SCLDDR],%[SCLPIN]	;force SCL low so SCL=H is short\n\t"
+     " ret \n\t"
+     "              ;; + 4 = 17C + 2X for acknowldge bit"
+     ::
+      [SCLDDR] "I"  (SCL_DDR), [SCLPIN] "I" (SCL_PIN), [SCLIN] "I" (SCL_IN),
+      [SDAOUT] "I" (SDA_OUT), [SCLOUT] "I" (SCL_OUT),
+      [SDADDR] "I"  (SDA_DDR), [SDAPIN] "I" (SDA_PIN), [SDAIN] "I" (SDA_IN)); 
+  return true; // fooling the compiler
+}
+#endif
+
+uint8_t i2c_read(bool last)
+#if I2C_HARDWARE
+{
+#if I2C_TIMEOUT
+  uint32_t start = millis();
+#endif
+    
+  TWCR = (1<<TWINT) | (1<<TWEN) | (last ? 0 : (1<<TWEA));
+  while(!(TWCR & (1<<TWINT))) {
+#if I2C_TIMEOUT
+    if (millis() - start > I2C_TIMEOUT) return 0xFF;
+#endif
+  }  
+  return TWDR;
+}
+#else
+{
+  __asm__ __volatile__ 
+    (
+     " ldi	r23,0x01 \n\t"
+     "_Li2c_read_bit: \n\t"
+#if I2C_PULLUP
+     " cbi      %[SCLOUT],%[SCLPIN]     ;disable SCL pull-up \n\t"
+#endif
+     " sbi	%[SCLDDR],%[SCLPIN]	;force SCL low         ;; 2C \n\t" 
+     " cbi	%[SDADDR],%[SDAPIN]	;release SDA(prev. ACK);; 4C \n\t"
+#if I2C_PULLUP
+     " sbi      %[SDAOUT],%[SDAPIN]     ;enable SDA pull-up \n\t"
+#endif
+     " nop \n\t"
+     " nop \n\t"
+     " nop \n\t"
+#if I2C_DELAY_COUNTER >= 1
+     " rcall	ass_i2c_delay_half	;delay T/2             ;; 4C+X \n\t" 
+#endif
+     " cbi	%[SCLDDR],%[SCLPIN]	;release SCL           ;; 6C + X \n\t" 
+#if I2C_PULLUP
+     " sbi      %[SCLOUT],%[SCLPIN]	;enable SCL pull-up \n\t"
+#endif
+#if I2C_DELAY_COUNTER >= 1
+     " rcall	ass_i2c_delay_half	;delay T/2             ;; 6C + 2X \n\t" 
+#endif
+     " cln                              ; clear N-bit          ;; 7C + 2X \n\t"
+     " nop \n\t "
+     " nop \n\t "
+     " nop \n\t "
+     " sbis     %[SCLIN], %[SCLPIN]     ;check for SCL high    ;; 9C +2X \n\t" 
+     " rcall    ass_i2c_wait_scl_high \n\t"
+     " brmi     _Li2c_read_return       ;return if timeout     ;; 10C + 2X\n\t"
+     " clc		  	        ;clear carry flag      ;; 11C + 2X\n\t" 
+     " sbic	%[SDAIN],%[SDAPIN]	;if SDA is high        ;; 11C + 2X\n\t" 
+     " sec			        ;set carry flag        ;; 12C + 2X\n\t" 
+     " rol	r23		        ;store bit             ;; 13C + 2X\n\t" 
+     " brcc	_Li2c_read_bit	        ;while receiv reg not full \n\t"
+     "                         ;; 15C + 2X for one bit loop \n\t" 
+     
+     "_Li2c_put_ack: \n\t"
+#if I2C_PULLUP
+     " cbi      %[SCLOUT],%[SCLPIN]     ;disable SCL pull-up \n\t"
+#endif
+     " sbi	%[SCLDDR],%[SCLPIN]	;force SCL low         ;; 2C \n\t" 
+     " cpi	r24,0                                          ;; 3C \n\t" 
+     " breq	_Li2c_put_ack_low	;if (ack=0) ;; 5C \n\t" 
+     " cbi	%[SDADDR],%[SDAPIN]	;release SDA \n\t" 
+#if I2C_PULLUP
+     " sbi      %[SDAOUT],%[SDAPIN]     ;enable SDA pull-up \n\t"
+#endif
+     " rjmp	_Li2c_put_ack_high \n\t" 
+     "_Li2c_put_ack_low:                ;else \n\t" 
+#if I2C_PULLUP
+     " cbi      %[SDAOUT],%[SDAPIN]     ;disable pull-up \n\t"
+#endif
+     " sbi	%[SDADDR],%[SDAPIN]	;force SDA low         ;; 7C \n\t" 
+     "_Li2c_put_ack_high: \n\t" 
+     " nop \n\t "
+     " nop \n\t "
+     " nop \n\t "
+#if I2C_DELAY_COUNTER >= 1
+     " rcall	ass_i2c_delay_half	;delay T/2             ;; 7C + X \n\t" 
+#endif
+     " cbi	%[SCLDDR],%[SCLPIN]	;release SCL           ;; 9C +X \n\t" 
+#if I2C_PULLUP
+     " sbi      %[SCLOUT],%[SCLPIN]	;enable SCL pull-up \n\t"
+#endif
+     " cln                              ;clear N               ;; +1 = 10C\n\t"
+     " nop \n\t "
+     " nop \n\t "
+     " sbis	%[SCLIN],%[SCLPIN]	;wait SCL high         ;; 12C + X\n\t" 
+     " rcall    ass_i2c_wait_scl_high \n\t"
+#if I2C_DELAY_COUNTER >= 1
+     " rcall	ass_i2c_delay_half	;delay T/2             ;; 11C + 2X\n\t" 
+#endif
+     "_Li2c_read_return: \n\t"
+     " nop \n\t "
+     " nop \n\t "
+#if I2C_PULLUP
+     " cbi      %[SCLOUT],%[SCLPIN]     ;disable SCL pull-up \n\t"
+#endif
+     "sbi	%[SCLDDR],%[SCLPIN]	;force SCL low so SCL=H is short\n\t"
+     " mov	r24,r23                                        ;; 12C + 2X \n\t"
+     " clr	r25                                            ;; 13 C + 2X\n\t"
+     " ret                                                     ;; 17C + X"
+     ::
+      [SCLDDR] "I"  (SCL_DDR), [SCLPIN] "I" (SCL_PIN), [SCLIN] "I" (SCL_IN),
+      [SDAOUT] "I" (SDA_OUT), [SCLOUT] "I" (SCL_OUT),
+      [SDADDR] "I"  (SDA_DDR), [SDAPIN] "I" (SDA_PIN), [SDAIN] "I" (SDA_IN) 
+     ); 
+  return ' '; // fool the compiler!
+}
+#endif
+
+#pragma GCC diagnostic pop
+
+#endif
+#endif