Contents
Realtek Chipset Documentation
This is a placeholder for publicly available and reverse engineered chipset documentation.
(this is an experiment)
Registers
0x0440 - RRSR
0x0440 |
RRSR |
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Response Rate control bitmap, HT40 channel (RTL8188E, RTL8192C only) |
RTL8188E, RTL8192E, RTL8192C |
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0..19 |
RATE_BITMAP |
Rate bitmap used for self-generated frames (RTS/CTS/BA/ACK) |
RTL8188E, RTL8192E, RTL8192C |
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21 |
RSC_LOWSUBCHNL |
1 = HT40 for the primary channel being below the channel centre |
RTL8188E |
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21 |
RSC_LOWSUBCHNL |
1 = HT40 for the secondary channel being below the channel centre |
RTL8192C |
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22 |
RSC_UPSUBCHNL |
1 = HT40 for the primary channel being above the channel centre |
RTL8188E |
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22 |
RSC_UPSUBCHNL |
1 = HT40 for the secondary channel being above the channel centre |
RTL8192C |
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23 |
SHORT |
1 = use short preamble for CCK |
RTL8188E, RTL8192E, RTL8192C |
The RRSR register is used for configuring RTS frame and self-generated response rate control. The rate bitmap matches the normal rate indexes documented elsewhere.
Notably, this is used for ACK/Block-ACK generation and CTS responses. For correct CTS operation in 11G / 11BG mixed mode, ensure that a CCK rate is available. For correct ACK/Block-ACK responses, ensure that an OFDM rate is available. If an OFDM rate is not available, ACK/Block-ACK responses to MCS frames will be at MCS7, which is extremely sub-optimal.
Also keep in mind that using higher CCK/OFDM/MCS rates in this bitmap will cause performance issues as those higher bitrates will not be robust in a noisy or normal signal environment. Please ensure the higher bitrates are masked out. The vendor and linux drivers only allow CCK1/CCK2 (for 2GHz), OFDM6/9/12 and MCS0 as basic rates.
Note that the initial RTS rate is configured elsewhere - in the TX descriptors if configured, and the INIRTS_RATE_SEL register (0x0480).
The UP/LOW sub channel register bits control whether to generate RTS/CTS exchanges on the primary, or primary + secondary channels when in 40MHz 11n operation.
0x0458 - AGGLEN_LMT (RTL8188E, RTL8192C)
0x0458 |
AGGLEN_LMT |
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Maximum number of MPDUs in a transmitted A-MPDU |
RTL8188E, RTL8192C |
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0..3 |
AGGLMT_MCS0 |
Maximum number of MPDUs in an A-MPDU for MCS0 |
RTL8188E, RTL8192C |
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4..7 |
AGGLMT_MCS1 |
Maximum number of MPDUs in an A-MPDU for MCS1 |
RTL8188E, RTL8192C |
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8..11 |
AGGLMT_MCS2 |
Maximum number of MPDUs in an A-MPDU for MCS2 |
RTL8188E, RTL8192C |
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12..15 |
AGGLMT_MCS3 |
Maximum number of MPDUs in an A-MPDU for MCS3 |
RTL8188E, RTL8192C |
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16..19 |
AGGLMT_MCS4 |
Maximum number of MPDUs in an A-MPDU for MCS4 |
RTL8188E, RTL8192C |
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20..23 |
AGGLMT_MCS5 |
Maximum number of MPDUs in an A-MPDU for MCS5 |
RTL8188E, RTL8192C |
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24..27 |
AGGLMT_MCS6 |
Maximum number of MPDUs in an A-MPDU for MCS6 |
RTL8188E, RTL8192C |
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28..31 |
AGGLMT_MCS7 |
Maximum number of MPDUs in an A-MPDU for MCS7 |
RTL8188E, RTL8192C |
This controls how many individual MPDUs to a single destination are combined into a single A-MPDU for transmission.
This allows the driver to artificially limit how long an A-MPDU may be - for example, limiting MCS0 to 1 or 2 MPDUs, whilst allowing an MCS7 MPDU to have up to 15 subframes.
Note that this applies to each spatial stream multiple of an MCS rate - MCS0 also applies to MCS8, MCS16, MCS24, MCS1 also applies to MCS9, MCS17, MCS25, etc.
0x0458 - AGGLEN_LMT (RTL8192E, RTL8812A, RTL8821A, RTL8814A)
0x0458 |
AGGLEN_LMT |
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Maximum size in bytes of a transmitted A-MPDU |
RTL8192E, RTL8812A, RTL8821A, RTL8814A |
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0..16 |
AGGLMT |
Maximum size of an A-MPDU in HT / VHT mode |
RTL8192E, RTL8812A, RTL8821A, RTL8814A |
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31 |
Unknown |
Configured in the vendor driver as '1' |
RTL8192E, RTL8812A, RTL8821A (NOT RTL8814A) |
This changed in the 11ac chipsets to become a maximum byte size instead of a maximum frame count. The vendor driver caps the value at 0xffff (64k - 1) for RTL8192E and RTL8821A, 0x1ffff (128k - 1) for RTL8812A, and 0x3ffff (256k - 1) for RTL8814A.
TX Descriptors (RTL8192CU)
(TBD)
- Setting the DRVRATE bit allows the DATARATE and RTSRATE fields to override the INIDATA / INIRTS registers to set the initial data and RTS/CTS rate.
Firmware API (RTL8192CU)
(TBD)
Firmware API (RTL8188EU)
(TBD)
Firmware API (RTL8192EU)
(TBD)
Commands
(TBD)
Responses / Notifications
(TBD)
Rate Control
(TBD)
Firmware API (RTL8812AU / RTL8821AU)
(TBD)