DisplayPort Audio Registers - 3.0 English

DisplayPort 1.4 TX Subsystem Product Guide (PG299)

Document ID
PG299
Release Date
2022-05-04
Version
3.0 English

The DisplayPort Audio registers are listed here.

Table 1. DisplayPort Audio
Offset Access Type Description
0x300 R/W

TX_AUDIO_CONTROL. Enables audio stream packets in main link and provides buffer control.

[19]: Set to 1 to mute the audio over link for MST STREAM 4. NA for SST

[18]: Set to 1 to mute the audio over link for MST STREAM 3. NA for SST

[17]: Set to 1 to mute the audio over link for MST STREAM 2. NA for SST

[16]: Set to 1 to mute the audio over link for SST. in MST, set to 1 to mute the Audio on STREAM 1

[5:4]: Audio Enable for STREAM 4:5 in MST. Default is STREAM1

[3]: Audio Enable for STREAM 4 in MST. NA for SST

[2]: Audio Enable for STREAM 3 in MST. NA for SST

[1]: Audio Enable for STREAM 2 in MST. NA for SST

[0]: Audio Enable for SST. In MST, Audio Enable for STREAM 1

0x304 R/W TX_AUDIO_CHANNELS. Used to input active channel count. Transmitter collects audio samples based on this information.

[2:0] Channel Count

0x308 WO

TX_AUDIO_INFO_DATA.

The IP can receive and buffer up to four Info Frames before they are processed and sent over the DP Link. The bits in register offset 0x6A0 indicate a full/overflow status of the internal "Info Frame Buffer", which holds these four Info Frames.

[31:0] Word of each Info Frame is formatted as per CEA 861-C Info Frame. Total of eight words per each Info Frame should be written in the following order:

1st word -
  • [31:24] = HB3
  • [23:16] = HB2
  • [15:8] = HB1
  • [7:0] = HB0

2nd word - DB3,DB2,DB1,DB0

....

8th word - DB27,DB26,DB25,DB24

The data bytes DB1...DBN of CEA Info frame are mapped as DB0-DBN-1.

No protection is provided for wrong operations by software. The capability to hold multiple Info Frames is useful in scenarios in which "Info Frames" corresponding to different features (such as Audio and HDR) are to be supported.

0x328 R/W TX_AUDIO_MAUD. M value of audio stream as computed by transmitter.

[23:0] = Unsigned value computed when audio clock and link clock are synchronous.

0x32C R/W TX_AUDIO_NAUD. N value of audio stream as computed by transmitter.

[23:0] = Unsigned value computed when audio clock and link clock are synchronous.

0x330 to 0x350 WO TX_AUDIO_EXT_DATA.

[31:0] = Word formatted as per Extension packet described in protocol standard.

Extended packet is fixed to 32 Bytes length. The controller has buffer space for only one extended packet. Extension packet address space can be used to send the audio Copy management packet/ISRC packet/VSC packets. TX is capable of sending any of these packets. VSC/EXT packets should use the same address space.

A total of nine words should be written in following order:

First word -
  • [31:24] = HB3
  • [23:16] = HB2
  • [15:8] = HB1
  • [7:0] = HB0

Second word - DB3,DB2,DB1,DB0

....

9th word - DB31, DB30, DB29, DB28

See the DisplayPort Standard for HB* definition.

No protection is provided for wrong operations by software. This is a key-hole memory. So, nine writes to this address space is required.

0x6A0 RO

TX_AUDIO_INFO_FRAME_BUFFER_STATUS.

Indicates full/overflow status of the internal Info Frame buffer which can hold up to 4 Info Frames (each of size 8 bytes as mentioned in the description of 0x308 register) received through offset register 0x308, those are to be processed by the IP.

For information about “Info Frame”, see the description of TX_AUDIO_INFO_DATA at offset register 0x308.

[0] = Internal Info Frame buffer “Full” status.

  • 1 - Indicates that the Info Frame buffer is full i.e. it has 4 Info Frames which are yet to be read and processed by the IP.
  • 0 - Indicates that the internal Info Frame buffer is ready to receive at least one Info frame through the offset register 0x308.

[1] = Internal Info Frame buffer “Overflow” status.

  • 1 - Indicates an error condition resulting from offset register 0x308 being written with new “Info frame”, even though the above bit[0] indicating “Full” is “1”.
  • 0 - Indicates that there is no overflow.