dev interface (i2c dev)

Devices can be assessed directly via the i2c-dev debug interface by giving location information on the command line to mxt-app.

The i2c-dev interface is documented in the Linux kernel source, in /Documentation/i2c/dev-interface.rst

The I2C debug interface support must be enabled using the CONFIG_I2C_CHARDEV kernel configuration option. It is enabled on a system if the directory /dev/i2c-* is present.

To use i2c-dev, provide a DEVICESTRING such as

 mxt-app -d i2c-dev:1-004a    /* Access a device on Bus 1, slave address 0x4a through I2C */

Messsages for the maXTouch device are read by polling. If a kernel driver is also present on the system, reading messages on interrupt, then no messages will be received by the tool. It is advised to disable the driver from getting interrupts.

Set the T18.COMMAND (byte 1) to 2 “Force the /CHG line high (inactive)” so the kernel driver does not receive interrupts.

There is no scanning support for I2C. This is because reading from every possible maXTouch address on every I2C bus might adversely affect some unrelated hardware that does not understand Object Protocol. You must manually identify the correct adapter and address by referencing the protocol guide or hardware schematic to fill in the DEVICESTRING option with the correct bus# and slave address.

It is possible to use the –flash command with a device already in bootloader mode by specifying the bootloader address.