If the esp32 is reset during a i2c read cycle the slave device may be in control of the SDA line.  

If the SDA line is held low, the esp32 cannot issue a START or STOP to recover the bus. 

The previous code did not correctly configure the SCL output pin, and it cycled SCL 9 times with SDA Low.  Since the slave device was in a READ cycle, it just continued outputting the bits of the current byte.  When the ACK/NAK bit space occurred, The low output value of SDA was interpreted as ACK so the slave device continued with the next byte.  It never terminated the READ cycle. 

This new code will correctly recover from an interrupted READ

add a troubleshooting hint

Fixes: https://github.com/espressif/arduino-esp32/issues/1724

* informations about sketch

* Update README.md

* ReSTART fix, Sequencing fix

pr #1665 introduce a problem with ReSTART, when solving this problem I found an interaction between the TxFifo refill, RxFifo empty and CMD[] fill.  during certain sequences a dataqueue command would be skipped, this skipping resulted in a mismatch between the contents of the TxFifo and the i2c command sequence.  The problem manifested as an ACK error. 
In addition to this required bug fix I propose:
* `Wire.begin()` be changed from a `void` to a `bool` this will allow the reset functionality of `Wire.begin()` to be reported.  Currently `Wire.begin()` attempts to reset the i2c Peripheral, but cannot report success/failure.
* `Wire.busy()` be added. this `bool` function returns the hardware status of the bus. This status can be use in multi-master environments for application level interleaving of commands, also in single master environment, it can be used to detect a 'hung' bus.  With the functional change to `Wire.begin()` this allows app level recover of a hung bus.
* `Wire.lastError()` value updated for all errors, previously when interleaving `Wire.endTransmission(false)` and `Wire.readTransmission(false)`, the 128 byte `Wire.write()` buffer was exhausted without generating and error(very exotic). I discovered this error when I created a sequence of directed reads to a EEPROM. Each directed read used 2 bytes of the 128 byte `write()` buffer, so after 64 consecutive ReSTART writes with ReSTART reads, `Wire()`  had no room to record the directed address bytes.  It generated just a NAK check without setting the EEPROMs internal register address.  The succeeding ReSTART read succeeded at incorrect address.
* Changes to the HAL layer:
** added `i2cGetStatus()` which returns the i2c peripheral status word, used to detect bus_busy currently
** added `i2cDebug()` programmatic control of debug buffer output
** changed `i2cAddQueue()` to allow data_only queue element this will allow a i2c transaction to use multiple data pointers.
** removed direct access to DumpInts(), DumpI2c() from app, use i2cDebug() to set trigger points 
 
*

* Update esp32-hal-i2c.c

* Update Wire.cpp

* ReSTART, Sequencing

pr #1665 introduce a problem with ReSTART, when solving this problem I found an interaction between the TxFifo refill, RxFifo empty and CMD[] fill.  during certain sequences a dataqueue command would be skipped, this skipping resulted in a mismatch between the contents of the TxFifo and the i2c command sequence.  The problem manifested as an ACK error. 
In addition to this required bug fix I propose:
* `Wire.begin()` be changed from a `void` to a `bool` this will allow the reset functionality of `Wire.begin()` to be reported.  Currently `Wire.begin()` attempts to reset the i2c Peripheral, but cannot report success/failure.
* `Wire.busy()` be added. this `bool` function returns the hardware status of the bus. This status can be use in multi-master environments for application level interleaving of commands, also in single master environment, it can be used to detect a 'hung' bus.  With the functional change to `Wire.begin()` this allows app level recover of a hung bus.
* `Wire.lastError()` value updated for all errors, previously when interleaving `Wire.endTransmission(false)` and `Wire.readTransmission(false)`, the 128 byte `Wire.write()` buffer was exhausted without generating and error(very exotic). I discovered this error when I created a sequence of directed reads to a EEPROM. Each directed read used 2 bytes of the 128 byte `write()` buffer, so after 64 consecutive ReSTART writes with ReSTART reads, `Wire()`  had no room to record the directed address bytes.  It generated just a NAK check without setting the EEPROMs internal register address.  The succeeding ReSTART read succeeded at incorrect address.
* Changes to the HAL layer:
** added `i2cGetStatus()` which returns the i2c peripheral status word, used to detect bus_busy currently
** added `i2cDebug()` programmatic control of debug buffer output
** changed `i2cAddQueue()` to allow data_only queue element this will allow a i2c transaction to use multiple data pointers.
** removed direct access to DumpInts(), DumpI2c() from app, use i2cDebug() to set trigger points 
 
*

* Forgot DebugFlags Return

@andriyadi found this, total brain fade on my part.

Because TCP is stream-based, an earlier read can 'take away' the "OK" response
from the device, so that a later read doesn't get the message.

* Added instructions for installation with boards manager (stolen directly from esp8266)

* changed to production link instead of dev

* Added to main README. Made mods to images as requested.

* Added links for development package

* Moved version images to README.md

* Just a little change for cleaner look

* Cleaned up README.md and boards_manager.md to make installation easier.

* Added instructions for installation with boards manager (stolen directly from esp8266)

* changed to production link instead of dev

* Added to main README. Made mods to images as requested.

* Added links for development package

* Added a define to format the spiffs in SPIFFS_Test.ino

* Uncommented the define

* Matched define names

speed up uploading data. Now there is no need to call time consuming
client.connected() method.

* Selective compilation

* Optimized component.mk

* Autoconnect WiFi now forces WiFi

When a package of size 0 arrives, "buf" is created, but never released. (Sorry, that was my mistake in the last patch)

* Add M5Stack-FIRE board

* updated m5stack-fire boards.txt

* remove pins 16 and 17

Sketch for ESP32 boards that allow them to connect to WPA/WPA2 Enterprise Networks.

If you receive a package with a data length of zero, parsePacket returns 0, but rx_buffer will exist. So if another parsePacket with no read access returns to zeros, there is still data that can be read. This example would not work: https://www.arduino.cc/en/Reference/EthernetUDPParsePacket

Also I added a check if rx_buffer exit when you try to flush it.

* Add ttgo-lora32-v1 folder to variants folder

* Add ttgo-lora32-v1 info to boards.txt

* Add defs to pins_arduino.h for I2C OLED and SPI LoRa radio pinouts as per @stickbreaker

This version no longer needs an interrupt for each byte transferred. It only needs interrupts for START, STOP, FIFO empty/Full or error conditions.  This dramatically reduces the interrupt overhead.  I think the prior version was causing an interrupt overload condition where the ISR was not able to process every interrupt as they happened.

EEPROM.h uses data types which are declared through Arduino.h but that file does not contain an #include directive for Arduino.h. This does not cause any problems when the EEPROM library is #included from a .ino file because the Arduino IDE automatically adds an #include directive for Arduino.h but this is not the case for .cpp files. If a .cpp file has an #include directive for EEPROM.h that does not follow an #include directive for Arduino.h then compilation fails:

E:\arduino\hardware\espressif\esp32\libraries\EEPROM/EEPROM.h:91:5: error: 'float_t' does not name a type

     float_t readFloat(int address);

     ^

E:\arduino\hardware\espressif\esp32\libraries\EEPROM/EEPROM.h:92:5: error: 'double_t' does not name a type

     double_t readDouble(int address);

     ^

E:\arduino\hardware\espressif\esp32\libraries\EEPROM/EEPROM.h:95:5: error: 'String' does not name a type

     String readString(int address);

     ^

E:\arduino\hardware\espressif\esp32\libraries\EEPROM/EEPROM.h:110:36: error: 'float_t' has not been declared

     size_t writeFloat(int address, float_t value);

                                    ^

E:\arduino\hardware\espressif\esp32\libraries\EEPROM/EEPROM.h:111:37: error: 'double_t' has not been declared

     size_t writeDouble(int address, double_t value);

                                     ^

E:\arduino\hardware\espressif\esp32\libraries\EEPROM/EEPROM.h:114:37: error: 'String' has not been declared

     size_t writeString(int address, String value);

* Initial support for ALKS variant

the 'eject' ERROR is and indication of an interrupt triggering without an source.  I am working to eliminate these serviceable interrupt.  This update increase stability on a HelTek Wifi Lora 32 board. with a SSD1306 OLED.  This update fixes a glaring error in the interrupt allocation code, the Interrupt mask was wrong.  I also dynamically adjust the FiFo thresholds based on Bus clockrate. The change to FiFo thresholds has reduced the number for 'eject' events.  I also change 'eject' from and ERROR to DEBUG.  An 'eject' event does not compromise i2c transmissions. It happens after a transaction has completed. 

Chuck.