Dependecies
 Arduino "Ethernet" library uses SPI
 esp32-hal-spi.h
 esp32-hal.h
 SPI.h
 SPI.h
 SD_Test.ino
 SD_time.ino
 sd_diskio.h
 SD.h
 SMMC_time.ino

---Categorized issues---
Address Mask 0x3F
 655 https://github.com/espressif/arduino-esp32/issues/655 User issue
 1419 https://github.com/espressif/arduino-esp32/issues/1419 Expired no answer
Bugfixes
 640 https://github.com/espressif/arduino-esp32/issues/640 Added `spiTransferBits'.
 https://github.com/espressif/arduino-esp32/commit/ab0ea2f6da9ca842fbb3bce90179daeb3580d3da
 1094 https://github.com/espressif/arduino-esp32/issues/1094 Fixed SPI user.ck_out_edge value.
 https://github.com/espressif/arduino-esp32/pull/1096
 1623 https://github.com/espressif/arduino-esp32/issues/1623 Add Arduino's SPI.transfer(buffer, size) function.
 https://github.com/espressif/arduino-esp32/pull/2136
	 https://github.com/arduino-libraries/Ethernet/releases/tag/2.0.0 Uses SPI.transfer().
 1814 https://github.com/espressif/arduino-esp32/issues/1814 Documentation fix
 The ESP32 has four SPI buses, however as of right now only two of them are available to use, HSPI and VSPI.
 Simply using the SPI API as illustrated in Arduino examples will use VSPI, leaving HSPI unused.
 3241 https://github.com/espressif/arduino-esp32/issues/3241 SPI.writeBytes() definition different ESP32 vs ESP8266.
 https://github.com/espressif/arduino-esp32/pull/3242
 3730 https://github.com/espressif/arduino-esp32/pull/3730 Added SPI_HAS_TRANSACTION.
 https://github.com/espressif/arduino-esp32/commit/7af4490fcc2b9f549414921d9a8ad1392303f4d8
 4558 https://github.com/espressif/arduino-esp32/issues/4558 Fixed SPI.setHwCs().
 https://github.com/espressif/arduino-esp32/pull/4559
 4935 https://github.com/espressif/arduino-esp32/issues/4935
 https://github.com/espressif/arduino-esp32/commit/a31f30529d3411a0a4a6549c75aadd6e725e7f60
 5787 https://github.com/espressif/arduino-esp32/issues/5787 Changed SPIClass::transfer() signature to match Arduino API.
 https://github.com/espressif/arduino-esp32/pull/6734
 https://github.com/arduino/ArduinoCore-API/blob/e03b65374c614130aa1b11597e07b3b5089a726d/api/HardwareSPI.h#L109-L111
 6404 https://github.com/espressif/arduino-esp32/issues/6404 SPI thread safety.
 https://github.com/espressif/arduino-esp32/pull/6425
 7465 https://github.com/espressif/arduino-esp32/issues/7465 Wrover-kit SPI Clarify documentation
Crashes
 1797 https://github.com/espressif/arduino-esp32/issues/1797 SPI crashes if user selects pins used by flash
 6601 https://github.com/espressif/arduino-esp32/issues/6601 Occassional lockup in spiWriteNL(). while(spi->dev->cmd.usr);
Custom SPI Driver
 2271 https://github.com/espressif/arduino-esp32/issues/2271 Custom SPI driver class. Interferes with Arduino SPI functions.
 4195 https://github.com/espressif/arduino-esp32/issues/4195 SPI GPIO Matrix in IDF. Custom user code.
Discussions
 https://github.com/espressif/arduino-esp32/discussions/6470 Custom SS lines
 https://github.com/espressif/arduino-esp32/discussions/6587 SPI.cpp sets _ss but never uses it
 https://github.com/espressif/arduino-esp32/discussions/6548 W5500 with SPI-ETH
Errata
 5137 https://github.com/espressif/arduino-esp32/issues/5137 ESP32 boot failure at power up due to GPIO12 invalid voltage.
 Solution is to burn eFuse.
Feature requests
 7063 https://github.com/espressif/arduino-esp32/issues/7063 Add QSPI mode. 3 parallel data streams with one clock.
Interrupt Safe?
 2000 https://github.com/espressif/arduino-esp32/issues/2000
 4295 https://github.com/espressif/arduino-esp32/issues/4295
 6404 https://github.com/espressif/arduino-esp32/issues/6404 Bugfix thread safety
Multiple SPI or alternate pins
 790 https://github.com/espressif/arduino-esp32/issues/790 VSPI & HSPI SPI buses simultaneously
 https://github.com/espressif/arduino-esp32/blob/master/libraries/SPI/examples/SPI_Multiple_Buses/SPI_Multiple_Buses.ino VSPI + HSPI example for ESP32s3
 1219 https://github.com/espressif/arduino-esp32/issues/1219 ESP32 Use 2 SPI ports
 User example code http://www.iotsharing.com/2017/05/how-to-use-arduino-esp32-to-store-data-to-sdcard.html
 2298 https://github.com/espressif/arduino-esp32/issues/2298 How to use HSPI with SPIClass
 When using the HSPI pins for interfacing SD card, the pinout says to connect MISO to GPIO12, but when it is connected we cannot upload the code since on GPIO 12 "boot fail if pulled high". So when we disconnect the MISO and upload the code, it doesn't work.
 Yes I was able to use the HSPI pins on ESP32, but uploading the code while MISO connected is still a problem for me. So when uploading the code, I disconnect the MISO jumper and when the code is uploaded, I connect it back.
 3572 https://github.com/espressif/arduino-esp32/issues/3572 Resolved
 5264 https://github.com/espressif/arduino-esp32/issues/5264 SPIClass cannot have more than one instance???
 5567 https://github.com/espressif/arduino-esp32/issues/5567 ESP32-S2 custom hardware. Unable to reproduce.
 5676 https://github.com/espressif/arduino-esp32/issues/5676 ESP32-S2 Doesn't work with SPI3.
 The final sketch snippet can be seen below, and works with SPI2 or SPI1 (FSPI & HSPI)
 It does not work with SPI3, and I'd love a solution as to why.
 Software SPI. SPIClass spi = SPIClass(HSPI);
 5897 https://github.com/espressif/arduino-esp32/issues/5897 User error. SPIClass spi = SPIClass(HSPI) cannot be local variable.
 5900 https://github.com/espressif/arduino-esp32/issues/5900 SPI HSPI with custom pins
 6252 https://github.com/espressif/arduino-esp32/issues/6252 SPIClass(HSPI) doesn't work but SPIClass(SPI) does.
 6372 https://github.com/espressif/arduino-esp32/issues/6372 SPIClass(VSPI) cannot be local variable.
 7543 https://github.com/espressif/arduino-esp32/issues/7543 ESP32-S3 Works with 1 SPI but not 2.
 7556 https://github.com/espressif/arduino-esp32/issues/7556 VSPI. Dynamic configuration of pointer to SPI no longer works due to transaction lock?
 7596 https://github.com/espressif/arduino-esp32/issues/7596 ESP32-C3 Documentation of SPI channels may be inconsistent
Misc
 149 https://github.com/espressif/arduino-esp32/issues/149 SPI slow due to transaction locking
 There are generally two ways to speed things up:
 Update all libraries to use proper multi-byte api on ESP32 (Espressif is rolling out own ILI9341 driver based on Adafruit's API)
 Disable hardware locking by adding #define CONFIG_DISABLE_HAL_LOCKS 1 to esp32-hal.h
 1427 https://github.com/espressif/arduino-esp32/issues/1427 spi_struct_t definition hidden
 struct spi_struct_t definition hidden in .c file. User defined struct in their code.
Refactoring
 6220 https://github.com/espressif/arduino-esp32/issues/6220 
 6597 https://github.com/espressif/arduino-esp32/issues/6597
 https://github.com/orgs/espressif/projects/3/views/5?pane=item&itemId=3266935
 https://github.com/orgs/espressif/projects/3/views/5?pane=item&itemId=4946329
SPI Slave Support. Needs to integrate with SPI.h as SPI can only be master or slave.
 619 https://github.com/espressif/arduino-esp32/issues/619
 Add support for SPISlave mode like the ESP8266 SPISlave arduino library
 https://github.com/esp8266/Arduino/tree/master/libraries/SPISlave
 https://gist.github.com/shaielc/e0937d68978b03b2544474b641328145
 Failed PR 1413 https://github.com/espressif/arduino-esp32/pull/1413
 IDF SPI Slave: https://github.com/espressif/esp-idf/tree/master/examples/peripherals/spi_slave
 igrr Status update: we need to investigate how much we can adhere to the official SPISlave library API if we decide to implement this one.
 696 https://github.com/espressif/arduino-esp32/issues/696
 https://github.com/espressif/esp-idf/blob/master/examples/peripherals/spi_slave/receiver/main/app_main.c
 1654 https://github.com/espressif/arduino-esp32/issues/1654
 5442 https://github.com/espressif/arduino-esp32/issues/5442
Unresolved (won't fix?)
 1889 https://github.com/espressif/arduino-esp32/issues/1889 ESP32 SPI SS doesn't match Arduino
 arduino SPI.begin() documentation states SS pin should be driven to OUTPUT and set HIGH. No action.
W5500 support
 5482 https://github.com/espressif/arduino-esp32/issues/5482 User code. Crashes on SPI. https://github.com/mkrasselt1/esp32-lan-w5500
 5913 https://github.com/espressif/arduino-esp32/issues/5913 Recommended using Arduino Ethernet lib: https://www.arduino.cc/en/Reference/Ethernet