P4-IO-Jacks — Transport via MQTT & NATS¶

The IO jacks are addressed via NATS and MQTT. Both use the four-part scheme Module → Jack → Interface → Direction:

Transport	Separator	Scheme
NATS	`.`	`ModuleSubject.Jack.Interface.Direction`
MQTT	`/`	`ModuleTopic/Jack/Interface/Direction`

Direction: r = subscribe (input byte stream) · w = publish (output byte stream)

Example – module gpio_abcdef123456, jack 0, reading UART:

NATS:  gpio_abcdef123456.0.uart.r
MQTT:  gpio_abcdef123456/0/uart/r

ModuleSubject / ModuleTopic = module ID, e.g. gpio_abcdef123456 (gpio_ + MAC identifier).
Jack = 0 … 3 (which of the four IO jacks, see P4-IO-Jacks Interfaces).
Interface = operating mode / channel:

Interface	Meaning
`port`	Digital I/O (4 bit) → PORT Mode
`i2c`	I²C transfers → I2C Read & Write
`uart`	serial payload data → UART Mode
`spi`	SPI data stream
`adc`	Analog input (IO-Jack 0 only, ADC0–ADC3)

Byte Stream Content¶

What is carried in the byte stream depends on the interface – not every interface uses Port-8:

Interface	Stream content
`port`	Port-8 encoded – 4-bit read/write (PORT Mode)
`uart`	raw UART payload data (bytes, not Port-8) → UART Mode
`i2c`	length-prefixed I²C protocol (not Port-8) → I2C Read & Write
`spi`	SPI data stream
`adc`	Analog values

Directions:
Output byte stream (publish / write): data or commands to the module.
Input byte stream (subscribe / read): data, responses & events from the module.