Raspberry Pi setup:
-------------------

= I2C communication =

To use the I2C communication:
- Edit the Raspberry Pi Configuration, go the interfaces pane:
  enable the I2C interface (disable the SPI and UART interfaces).

- Edit /boot/config.txt and make sure the following parameters are set:
  # Set a fixed core frequency to avoid frequency changes depending on processor load, I2C clock is derived from this one.
  core_freq=250

  # Set Fast mode I2C (400kHz)
  dtparam=i2c_arm=on,i2x_arm_baudrate=400000


How to build:
-------------

Ensure the correct RFAL variant is set in CMakeLists.txt, e.g.:
    set(RFAL_VARIANT "st25r3916" CACHE STRING "Select the RFAL library")

Then

Go to the build directory

$ mkdir -p linux_demo/build
$ cd linux_demo/build

Choose the build type:
1. For the Reader/Writer demo:
$ cmake ..
2. For the Card Emulation-only demo:
$ cmake -DCARD_EMULATION_ONLY=ON ..

Then build:

$ make


How to run from the build folder:
---------------------------------

$ sudo ./demo/nfc_demo_<variant>
or
$ sudo ./demo/nfc_demo_<variant>_CE


Note on the Linux SPI driver:
-----------------------------
Check SPI driver version with:
$ modinfo spidev

With recent Linux kernel and SPI driver, you may encounter "Failed to get line handle for GPIO pin8 (errno 16)"

This occurs with SPI driver v5.4.51, because it reserves GPIO8 for SPI0 CS0.
This prevents the nfc_demo_<variant> to control this GPIO itself.
To overcome this, tell the SPI driver to use another GPIO to control the Chip Select signal.
To do so on the Raspberry Pi, add the following to /boot/config.txt:
dtoverlay spi0-cs,cs0_pin=6

This was not needed for SPI driver v4.19.97.

Another issue can occur with SPI driver v5.10.11-v8+: The kernel sets up SPI0 and SPI1.
You may encounter "Failed to get line handle for GPIO pin7 (errno 16)"
GPIO 7 is used by SPI1 CE1, preventing to use it by the NFC demo receiving interrupts on GPIO ST25R_INT_PIN.
To overcome this, tell the SPI driver to setup only one SPI bus.
To do so on the Raspberry Pi, add the following to /boot/config.txt:
dtoverlay spi0-1cs
or tell it to use another GPIO to control the Chip Select signal. Add the following to /boot/config.txt:
dtoverlay spi0-1cs,cs0_pin=6

A convenient way to check GPIO configuration is using the shell command $ gpio readall

$ gpio readall
 +-----+-----+---------+------+---+---Pi 3B--+---+------+---------+-----+-----+
 | BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
 +-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
 |     |     |    3.3v |      |   |  1 || 2  |   |      | 5v      |     |     |
 |   2 |   8 |   SDA.1 |   IN | 1 |  3 || 4  |   |      | 5v      |     |     |
 |   3 |   9 |   SCL.1 |   IN | 1 |  5 || 6  |   |      | 0v      |     |     |
 |   4 |   7 | GPIO. 7 |   IN | 1 |  7 || 8  | 1 | IN   | TxD     | 15  | 14  |
 |     |     |      0v |      |   |  9 || 10 | 1 | IN   | RxD     | 16  | 15  |
 |  17 |   0 | GPIO. 0 |   IN | 0 | 11 || 12 | 0 | IN   | GPIO. 1 | 1   | 18  |
 |  27 |   2 | GPIO. 2 |   IN | 0 | 13 || 14 |   |      | 0v      |     |     |
 |  22 |   3 | GPIO. 3 |   IN | 0 | 15 || 16 | 0 | IN   | GPIO. 4 | 4   | 23  |
 |     |     |    3.3v |      |   | 17 || 18 | 0 | IN   | GPIO. 5 | 5   | 24  |
 |  10 |  12 |    MOSI | ALT0 | 0 | 19 || 20 |   |      | 0v      |     |     |
 |   9 |  13 |    MISO | ALT0 | 0 | 21 || 22 | 0 | IN   | GPIO. 6 | 6   | 25  |
 |  11 |  14 |    SCLK | ALT0 | 0 | 23 || 24 | 1 | OUT  | CE0     | 10  | 8   |
 |     |     |      0v |      |   | 25 || 26 | 0 | IN   | CE1     | 11  | 7   | // Pay attention to 'CE1' set on pin 7 with direction 'IN'
 |   0 |  30 |   SDA.0 |   IN | 1 | 27 || 28 | 1 | IN   | SCL.0   | 31  | 1   |
 |   5 |  21 | GPIO.21 |   IN | 1 | 29 || 30 |   |      | 0v      |     |     |
 |   6 |  22 | GPIO.22 |   IN | 1 | 31 || 32 | 0 | IN   | GPIO.26 | 26  | 12  |
 |  13 |  23 | GPIO.23 |   IN | 0 | 33 || 34 |   |      | 0v      |     |     |
 |  19 |  24 | GPIO.24 |   IN | 0 | 35 || 36 | 0 | IN   | GPIO.27 | 27  | 16  |
 |  26 |  25 | GPIO.25 |   IN | 0 | 37 || 38 | 0 | IN   | GPIO.28 | 28  | 20  |
 |     |     |      0v |      |   | 39 || 40 | 1 | IN   | GPIO.29 | 29  | 21  |
 +-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
 | BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
 +-----+-----+---------+------+---+---Pi 3B--+---+------+---------+-----+-----+

This is a working configuration set with:
dtparam=spi=off
dtoverlay=spi0-1cs


Debugging:
----------
$ cmake -DCMAKE_BUILD_TYPE=Debug ..
$ make
sudo gdbtui ./demo/nfc_demo_<variant>
or
sudo gdbtui ./demo/nfc_demo_<variant>_CE
to set a breakpoint:
b <function>
b <filename>:<linenumber>
r to run
s to step into the code (go down into the function)
up to go one level up
n to go to next line
bt to show backtrace
CTRL-C to break
c to continue
info b to list the breakpoints
del n to delete breakpoint