Chest board link

The chest board is the only USB device nao-rs talks to for the body. It is the hub for everything below the neck. This page describes the link as recorded from the robot and as nao-rs implements it. Parts marked (inferred) are read from the traffic and not yet confirmed otherwise.

The device

Start-up

The exchange

Every exchange has three steps:

1. Bulk OUT on EP1: one frame, 20 ms timeout.
2. Vendor IN request 0x14, 5 bytes: 2a followed by the CRC of the frame just sent. The chest board acknowledges the frame.
3. Bulk IN on EP1, up to 512 bytes, 20 ms timeout: the answer frame. When nothing is ready the read times out, and vendor IN request 0x15 (2 bytes) asks for the chest board's status (inferred).

A bulk read takes about 0.7 ms.

Frames

The CRC is the standard CRC-32 (the one zlib computes). A frame holds up to 255 messages and at most 4 KB. A frame whose length table doesn't add up decodes to no messages. HAL's decoder writes past 255 entries without a bound check; nao-rs stops at 255.

Messages

Every message starts with three bytes: kind, bus, address.

Byte 2 is the board address (see Boards) or a register.

Preferences

The chest board stores a 4,635-byte preference block, read in 32-byte pieces and checked with a CRC. It holds typed key-value pairs, among them:

• the body id and body version;
• the stored serial number of every board;
• the joint zero positions;
• the foot pressure sensors' gains and offsets;
• the inertial unit's offsets.

naoctl prefs prints all of them. nao-rs reads all 76 values HAL logs, and every one is identical to HAL's.

The motor board handshake

1. nao-rs sends a 4-byte request, 00 <bus> <board> 20, to each board.
2. The board answers with 32 bytes: 16 bytes of status, then 16 bytes of configuration: its serial number (equal to its stored serial number in the preferences; the foot boards send 0), the configuration version, the hardware revision, the board type and the fields used at run time.
3. The version is checked against the accepted list. A rejected board is asked again, three times in all, and then left uninitialized.
4. An accepted board gets one command afterwards: 01 <bus> <board> 07 for joint boards, 01 <bus> <board> 08 for hand and foot boards (inferred: start).

HAL does not send a configuration table to the boards; it only reads theirs. Every board of a NAO6 updated by NAOqi 2.8.7 reports version 11 (0b). HAL 2.8.5 accepts only 10, which is why the motors of such a robot don't start under HULKs-OS. The bytes HAL takes from the configuration after the check have the same meaning in versions 10 and 11. nao-rs accepts [10] by default, like HAL; accepting 11 is the motor session's step (planned).

The chest board tools

Aldebaran's three chest board tools are ported onto the same link. They need the chest board free: stop hulk (or HAL) first.

None of the tools puts the chest board into its boot loader. They are not in the robot bundle yet; build them from the drivers repository.