Hi
This is an updated version of the proposal for adding an api for
HDMI-CEC to V4L2.
Main difference is the support of AV.link EN 50157-2-[123]. (thanks to
Daniel Glöckner)
Author: Martin Bugge <marbugge@xxxxxxxxx>
Date: Fri, 11th of March 2010
=============================
This is a proposal for adding a Consumer Electronic Control (CEC) API to
V4L2.
This document describes the changes and new ioctls needed.
Version 1.
Initial version
Version 2.
Added support for AV.link EN 50157-2-[123].
Background
==========
CEC is a protocol that provides high-level control functions between
various audiovisual products.
It is an optional supplement to the High-Definition Multimedia Interface
Specification (HDMI).
In short: CEC uses pin 13 on the HDMI connector to transmit and receive
small data-packets
(maximum 16 bytes including a 1 byte header) at low data
rates (~400 bits/s).
A CEC device may have any of 15 logical addresses (0 - 14).
(address 15 is broadcast and some addresses are reserved)
Physical layer is a one-wire bidirectional serial bus that uses the
industry-standard AV.link, see [3].
Due to this the proposed ioctls and events are meant to cover expansion
for the protocols in [3].
References
==========
[1] High-Definition Multimedia Interface Specification version 1.3a,
Supplement 1 Consumer Electronic Control (CEC).
http://www.hdmi.org/manufacturer/specification.aspx
[2]
http://www.hdmi.org/pdf/whitepaper/DesigningCECintoYourNextHDMIProduct.pdf
[3] Domestic and similar electronic equipment interconnection requirements
AV.link. EN 50157-2-[123]
Proposed solution
=================
Two new ioctls:
VIDIOC_AV_LINK_CAP (read)
VIDIOC_AV_LINK_CMD (read/write)
VIDIOC_AV_LINK_CAP:
-------------------------------
#define AV_LINK_CAP_MODE_CEC (1 << 0)
#define AV_LINK_CAP_MODE_1 (1 << 1)
#define AV_LINK_CAP_MODE_2 (1 << 2)
#define AV_LINK_CAP_MODE_3 (1 << 3)
struct vl2_av_link_cap {
__u32 capabilities;
__u32 logicaldevices;
__u32 reserved[14];
};
The capabilities field will indicate which protocols/formats this HW
supports.
* AV link mode CEC:
logicaldevices: 1 -> 14, this HW supports n logical devices
simultaneously.
* AV link mode 1:
logicaldevices: not used.
* AV link mode 2:
Same as AV link mode CEC.
* AV link mode 3:
logicaldevices: not used.
reserved: for future use.
VIDIOC_AV_LINK_CMD:
-------------------
The command ioctl is used both for configuration and to receive/transmit
data.
/* mode 1 */
struct avl_mode1_conf {
__u32 enable;
__u32 upstream_Qty;
__u32 downstream_Qty;
};
struct avl_mode1 {
__u32 head;
__u32 Qty;
__u32 tx_status;
__u32 tx_status_Qty;
};
/* mode 2, 3 and CEC */
struct avl_conf {
__u32 enable;
__u32 index;
__u32 addr;
};
struct avl {
__u32 len;
__u8 msg[16];
__u32 tx_status;
};
struct v4l2_av_link_cmd {
__u32 command;
__u32 mode;
__u32 reserved[2];
union {
struct avl_mode1_conf avlm1_conf;
struct avl_mode1 avlm1;
struct avl_conf conf;
struct avl avl;
__u32 raw[12];
};
};
/* command */
#define V4L2_AV_LINK_CMD_CONF (1)
#define V4L2_AV_LINK_CMD_TX (2)
#define V4L2_AV_LINK_CMD_RX (3)
/* mode */
#define AV_LINK_CMD_MODE_CEC (1)
#define AV_LINK_CMD_MODE_1 (2)
#define AV_LINK_CMD_MODE_2 (3)
#define AV_LINK_CMD_MODE_3 (4)
/* Tx status */
#define V4L2_AV_LINK_STAT_TX_OK (0)
#define V4L2_AV_LINK_STAT_TX_ARB_LOST (1)
#define V4L2_AV_LINK_STAT_TX_RETRY_TIMEOUT (2)
#define V4L2_AV_LINK_STAT_TX_BROADCAST_REJECT (3)
Not every tx status is applicable for all modes, see table 1.
|-----------------------------------------------------|
| Av link Mode | CEC | 1 | 2 | 3 |
|-----------------------------------------------------|
| Status | | | | |
|-----------------------------------------------------|
| TX_OK | a | n/a | a | n/a |
|-----------------------------------------------------|
| TX_ARB_LOST | a | n/a | a | a |
|-----------------------------------------------------|
| TX_RETRY_TIMEOUT | a | n/a | a | a |
|-----------------------------------------------------|
| TX_BROADCAST_REJECT | a | n/a | a | n/a |
|-----------------------------------------------------|
Table 1: tx status versus mode.
a: applicable
n/a: not applicable
Configuration command:
----------------------
* AV link mode CEC:
Must be done for each logical device address which is to be
enabled on this HW. Maximum number of logical devices
is found with the capability ioctl.
conf:
index: 0 -> number_of_logical_devices-1
enable: true/false
addr: logical address
* AV link mode 1:
In mode 1 the frame length is fixed to 21 bits (including the
start sequence).
Some of these bits (Qty 1 - 6) can be arbitrated by the receiver
to signal
supported formats/standards.
conf:
enable: true/false
upstream_Qty: QTY bits 1-6
downstream_Qty: QTY bits 1-6
|------------------------------------------------|
| Bits: | 31 - 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|------------------------------------------------|
| Qty bits | x | x | 6 | 5 | 4 | 3 | 2 | 1 |
|------------------------------------------------|
Qty bits 1-6 mapping (x: not used)
* AV link mode 2:
Same as AV link mode CEC.
* AV link mode 3: TBD. Chances are that nobody ever used this
conf:
index: 0 (not used)
enable: true/false
addr: 0 (not used)
Tx/Rx command:
--------------
* AV link mode CEC:
len: length of message in bytes (data + header).
msg: the raw message received/transmitted.
tx_status: tx status in blocking mode.
* AV link mode 1:
Frame received/transmitted:
head:
|-------------------------------------------------|
| Bits: | 31 - 4 | 3 | 2 | 1 | 0 |
|-------------------------------------------------|
| head bits: | x | DIR | /PAS | /NAS | /DES |
|-------------------------------------------------|
Qty: Quality bits 1 - 16;
|---------------------------------------|
| Bits: | 31 - 16 | 15 | 14 - 1 | 0 |
|---------------------------------------|
| Qty bits | x | 16 | 15 - 2 | 1 |
|---------------------------------------|
x: not used
In blocking mode only:
tx_status: tx status.
tx_status_Qty: which Qty bits 1 - 6 bits was arbitrated during
transmit.
* AV link mode 2:
len: length of message in bytes (data + command block).
msg: the raw message received/transmitted (without the start
sequence).
tx_status: tx status in blocking mode.
* AV link mode 3: TBD. Chances are that nobody ever used this
len: length of message in bits, maximum 96 bits.
msg: the raw message received/transmitted. (without the start
sequence).
tx_status: tx status in blocking mode.
Events
------
In the case of non-blocking mode the driver will issue the following events:
V4L2_EVENT_AV_LINK_TX
V4L2_EVENT_AV_LINK_RX
V4L2_EVENT_AV_LINK_TX
-----------------
* transmit is complete with the following status:
Add an additional struct to the struct v4l2_event
struct v4l2_event_av_link_tx {
__u32 status;
__u32 tx_status_mode1_Qty;
};
* The status field is the same as in blocking mode described above.
* tx_status_mode1_Qty apply only to mode 1.
V4L2_EVENT_AV_LINK_RX
-----------------
* received a complete message
Use the VIDIOC_AV_LINK_CMD to read the message.
Comments ?
Martin Bugge
--
Martin Bugge - Tandberg (now a part of Cisco)
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