i2c_master_slave/i2c_master_slave_dma examples have undocumented requirements

[hannobraun]

The examples are designed to run without external hardware, but they still seem to require pull-up resistors (which makes sense). At least I think this is what makes the difference. The only board I can get them to run on is part of a non-trivial test stand, so I can't be sure.

The solution here is to verify that pull-up resistors are actually what's missing (10 kOhm on the SCL and SDA pins should work) and either document that in the examples, or figure out if the built-in pull-up resistors can be configured in software (never tried that).

[david-sawatzke]

This is probably also the case for the i2c_eeprom example.