STDIO over Bluetooth for Pico_W C SDK

This repositioy implements a driver to provide STDIO (printf, scanf, etc.) over Bluetooth. With it you can use a Bluetooth serial console on your phone or tablet to interact with your Pico_W project without any physical connection. Convenient if the Pico is embedded in a project.

It should be noted that the Pico SDK documentation states (section 8.61.1) that:

the API for adding additional input output devices is not yet considered stable

The code is based heavily on the "spp_counter" example from the BlueKitchen BTStack.

To enable Bluetooth access, include the following near the start of your program:

#include "stdio_bt.h"

    stdio_init_all();
    cyw43_arch_init ();
    stdio_bt_init ();
    stdio_set_driver_enabled (&stdio_bt, true);

Your CMakeLists.txt file will need to include something like:

    add_subdirectory (/path/to/bluetooth_stdio stdio_bt)
    target_compile_definitions(bbcbasic PUBLIC
      -DBT_NAME="Pico"
      -DPICO_FLASH_BANK_TOTAL_SIZE=0x2000           # = 2 * FLASH_SECTOR_SIZE
      -DPICO_FLASH_BANK_STORAGE_OFFSET=0x1FE000     # = PICO_FLASH_SIZE_BYTES - PICO_FLASH_BANK_TOTAL_SIZE
      )
    target_link_libraries(${PROJECT_NAME}
        bluetooth_stdio
        pico_cyw43_arch_none
        )

__BT_NAME__ defines the name that will be given to the Bluetooth service when you search for a connection.

Alternately, to have your software specify the name given to the Bluetooth service, start your program with:

#include "stdio_bt.h"

    stdio_init_all();
    cyw43_arch_init ();
    if ( !stdio_bt_init_name ("Your_Service_Name") )
        panic ("Failed to initialise service name\n");
    stdio_set_driver_enabled (&stdio_bt, true);

The Bluetooth code uses 128 KB of flash memory to save paired connections. The __PICO_FLASHBANK*__ defines specify the location used for this. By default this is located at the top of flash memory (as per the above example). If you are using some of the flash memory to store a filesystem, then you will have to ensure that the two do not overlap. It is not currently clear how to configure to use another storage medium (such as SD card) to store this data.

If using WiFi as well as Bluetooth, then replace __pico_cyw43_arch_none__ appropriately.

The test folder contains a simple test program. Build this in the standard fashion

cd bluetooth-stdio/test
mkdir test
cd test
cmake ..
make

Then copy the resulting __bt_test.uf2 onto a Pico W. Connect a Bluetooth serial terminal to the resulting Pico__ device. Lines typed into the terminal will be echoed back.

Note that the test program is not protected against very long (>511 characters) input lines.