Head devices

The nine chips on the head's I2C bus, their addresses, what one bus cycle sends, and the LoLA quirks nao-rs keeps on the wire.

On the NAO6, LoLA (not HAL) drives the head. Its devices sit behind a USB-I2C bridge in the head, which Linux exposes as an I2C bus; udev links it as /dev/i2c-head (it is /dev/i2c-9 on our robot). nao-rs drives the same nine chips with the same bytes, one transaction per cycle.

The chips

Address (7-bit)	Address (8-bit)	Chip	Role
`0x66`	`0xCC`	TLC59116	Eye LEDs, blue
`0x64`	`0xC8`	TLC59116	Eye LEDs, green
`0x62`	`0xC4`	TLC59116	Eye LEDs, red
`0x61`	`0xC2`	TLC59116	Left ear LEDs
`0x60`	`0xC0`	TLC59116	Right ear LEDs
`0x65`	`0xCA`	TLC59116	Skull LEDs
`0x28`	`0x50`	CAP1203	The three head touch pads
`0x40`	`0x80`	INA230	Head power monitor: voltage, current, power
`0x48`	`0x90`	TMP100	Face board temperature

The LED drivers' channel mapping is on the LEDs page.

Start-up

The devices are created in the order of the table. Each LED driver starts with its register image only, without bus traffic. The touch controller, the power monitor and the temperature sensor get their register settings in 2-byte writes, one transfer each. The start-up takes about 70 ms, most of it the touch controller's calibration.

One bus cycle

One cycle is one I2C_RDWR transfer with 16 messages, or 18 when the temperature is due:

Device	Messages
6 LED drivers	One 30-byte write each: the auto-increment register byte, then all 29 registers from `MODE1` to `IREF`. Only the PWM bytes change
Touch controller	Read the sensor input status (1 byte), then write 0 to the main control register, which clears the latched status
Power monitor	Three register reads (bus voltage, power, current), then the configuration write
Temperature sensor	One read, when more than 300 ms have passed since the last one (about every 20th to 25th cycle)

A transfer takes about 6 ms on the bus (5.8 ms measured with nao-rs). The state a cycle returns is decoded from the previous transfer, as in LoLA. After a failed transfer, the next transfers are split into smaller ones for a while.

LED current

Each LED driver's output current comes from its IREF register:

Chip	Current	`IREF`
Eyes (3 chips)	5 mA	`0x30`
Ears (2 chips)	12 mA	`0xF3`
Skull	6 mA	`0x22`

LoLA quirks kept on the wire

nao-rs sends what LoLA sends, including two mistakes, because changing bytes the chips have always received is a change we'd have to test separately:

The power monitor's reset value is written in the wrong byte order, so the chip receives 0x0080 and is never reset.
Its configuration word shifts the averaging and conversion-time fields by 11, 8 and 5 bits instead of the data sheet's 9, 6 and 3. The robot receives 0x1487.

Touch pads

The touch controller reports three channels. The runtime's state lists them as front, middle and rear (touch indices 1, 2 and 3), which are the controller's channels 2, 1 and 0. A touch reads 1, no touch 0. All three at once trip the death switch. The physical order still needs one touch of each pad to confirm.

Checked live

naoctl head on the robot: eyes cycling red, green and blue (seen by eye), 24.8 V, 10.7 W, 43 to 47 °C, 5.8 ms per transfer.