+/**
+ * To calculate a txpower setting for a given desired target txpower, channel,
+ * modulation bit rate, and transmitter chain (4965 has 2 transmitters to
+ * support MIMO and transmit diversity), driver must do the following:
+ *
+ * 1) Compare desired txpower vs. (EEPROM) regulatory limit for this channel.
+ * Do not exceed regulatory limit; reduce target txpower if necessary.
+ *
+ * If setting up txpowers for MIMO rates (rate indexes 8-15, 24-31),
+ * 2 transmitters will be used simultaneously; driver must reduce the
+ * regulatory limit by 3 dB (half-power) for each transmitter, so the
+ * combined total output of the 2 transmitters is within regulatory limits.
+ *
+ *
+ * 2) Compare target txpower vs. (EEPROM) saturation txpower *reduced by
+ * backoff for this bit rate*. Do not exceed (saturation - backoff[rate]);
+ * reduce target txpower if necessary.
+ *
+ * Backoff values below are in 1/2 dB units (equivalent to steps in
+ * txpower gain tables):
+ *
+ * OFDM 6 - 36 MBit: 10 steps (5 dB)
+ * OFDM 48 MBit: 15 steps (7.5 dB)
+ * OFDM 54 MBit: 17 steps (8.5 dB)
+ * OFDM 60 MBit: 20 steps (10 dB)
+ * CCK all rates: 10 steps (5 dB)
+ *
+ * Backoff values apply to saturation txpower on a per-transmitter basis;
+ * when using MIMO (2 transmitters), each transmitter uses the same
+ * saturation level provided in EEPROM, and the same backoff values;
+ * no reduction (such as with regulatory txpower limits) is required.
+ *
+ * Saturation and Backoff values apply equally to 20 Mhz (legacy) channel
+ * widths and 40 Mhz (.11n fat) channel widths; there is no separate
+ * factory measurement for fat channels.
+ *
+ * The result of this step is the final target txpower. The rest of
+ * the steps figure out the proper settings for the device to achieve
+ * that target txpower.
+ *
+ *
+ * 3) Determine (EEPROM) calibration subband for the target channel, by
+ * comparing against first and last channels in each subband
+ * (see struct iwl4965_eeprom_calib_subband_info).
+ *
+ *
+ * 4) Linearly interpolate (EEPROM) factory calibration measurement sets,
+ * referencing the 2 factory-measured (sample) channels within the subband.
+ *
+ * Interpolation is based on difference between target channel's frequency
+ * and the sample channels' frequencies. Since channel numbers are based
+ * on frequency (5 MHz between each channel number), this is equivalent
+ * to interpolating based on channel number differences.
+ *
+ * Note that the sample channels may or may not be the channels at the
+ * edges of the subband. The target channel may be "outside" of the
+ * span of the sampled channels.
+ *
+ * Driver may choose the pair (for 2 Tx chains) of measurements (see
+ * struct iwl4965_eeprom_calib_ch_info) for which the actual measured
+ * txpower comes closest to the desired txpower. Usually, though,
+ * the middle set of measurements is closest to the regulatory limits,
+ * and is therefore a good choice for all txpower calculations (this
+ * assumes that high accuracy is needed for maximizing legal txpower,
+ * while lower txpower configurations do not need as much accuracy).
+ *
+ * Driver should interpolate both members of the chosen measurement pair,
+ * i.e. for both Tx chains (radio transmitters), unless the driver knows
+ * that only one of the chains will be used (e.g. only one tx antenna
+ * connected, but this should be unusual). The rate scaling algorithm
+ * switches antennas to find best performance, so both Tx chains will
+ * be used (although only one at a time) even for non-MIMO transmissions.
+ *
+ * Driver should interpolate factory values for temperature, gain table
+ * index, and actual power. The power amplifier detector values are
+ * not used by the driver.
+ *
+ * Sanity check: If the target channel happens to be one of the sample
+ * channels, the results should agree with the sample channel's
+ * measurements!
+ *
+ *
+ * 5) Find difference between desired txpower and (interpolated)
+ * factory-measured txpower. Using (interpolated) factory gain table index
+ * (shown elsewhere) as a starting point, adjust this index lower to
+ * increase txpower, or higher to decrease txpower, until the target
+ * txpower is reached. Each step in the gain table is 1/2 dB.
+ *
+ * For example, if factory measured txpower is 16 dBm, and target txpower
+ * is 13 dBm, add 6 steps to the factory gain index to reduce txpower
+ * by 3 dB.
+ *
+ *
+ * 6) Find difference between current device temperature and (interpolated)
+ * factory-measured temperature for sub-band. Factory values are in
+ * degrees Celsius. To calculate current temperature, see comments for
+ * "4965 temperature calculation".
+ *
+ * If current temperature is higher than factory temperature, driver must
+ * increase gain (lower gain table index), and vice versa.
+ *
+ * Temperature affects gain differently for different channels:
+ *
+ * 2.4 GHz all channels: 3.5 degrees per half-dB step
+ * 5 GHz channels 34-43: 4.5 degrees per half-dB step
+ * 5 GHz channels >= 44: 4.0 degrees per half-dB step
+ *
+ * NOTE: Temperature can increase rapidly when transmitting, especially
+ * with heavy traffic at high txpowers. Driver should update
+ * temperature calculations often under these conditions to
+ * maintain strong txpower in the face of rising temperature.
+ *
+ *
+ * 7) Find difference between current power supply voltage indicator
+ * (from "initialize alive") and factory-measured power supply voltage
+ * indicator (EEPROM).
+ *
+ * If the current voltage is higher (indicator is lower) than factory
+ * voltage, gain should be reduced (gain table index increased) by:
+ *
+ * (eeprom - current) / 7
+ *
+ * If the current voltage is lower (indicator is higher) than factory
+ * voltage, gain should be increased (gain table index decreased) by:
+ *
+ * 2 * (current - eeprom) / 7
+ *
+ * If number of index steps in either direction turns out to be > 2,
+ * something is wrong ... just use 0.
+ *
+ * NOTE: Voltage compensation is independent of band/channel.
+ *
+ * NOTE: "Initialize" uCode measures current voltage, which is assumed
+ * to be constant after this initial measurement. Voltage
+ * compensation for txpower (number of steps in gain table)
+ * may be calculated once and used until the next uCode bootload.
+ *
+ *
+ * 8) If setting up txpowers for MIMO rates (rate indexes 8-15, 24-31),
+ * adjust txpower for each transmitter chain, so txpower is balanced
+ * between the two chains. There are 5 pairs of tx_atten[group][chain]
+ * values in "initialize alive", one pair for each of 5 channel ranges:
+ *
+ * Group 0: 5 GHz channel 34-43
+ * Group 1: 5 GHz channel 44-70
+ * Group 2: 5 GHz channel 71-124
+ * Group 3: 5 GHz channel 125-200
+ * Group 4: 2.4 GHz all channels
+ *
+ * Add the tx_atten[group][chain] value to the index for the target chain.
+ * The values are signed, but are in pairs of 0 and a non-negative number,
+ * so as to reduce gain (if necessary) of the "hotter" channel. This
+ * avoids any need to double-check for regulatory compliance after
+ * this step.
+ *
+ *
+ * 9) If setting up for a CCK rate, lower the gain by adding a CCK compensation
+ * value to the index:
+ *
+ * Hardware rev B: 9 steps (4.5 dB)
+ * Hardware rev C: 5 steps (2.5 dB)
+ *
+ * Hardware rev for 4965 can be determined by reading CSR_HW_REV_WA_REG,
+ * bits [3:2], 1 = B, 2 = C.
+ *
+ * NOTE: This compensation is in addition to any saturation backoff that
+ * might have been applied in an earlier step.
+ *
+ *
+ * 10) Select the gain table, based on band (2.4 vs 5 GHz).
+ *
+ * Limit the adjusted index to stay within the table!
+ *
+ *
+ * 11) Read gain table entries for DSP and radio gain, place into appropriate
+ * location(s) in command (struct iwl4965_txpowertable_cmd).
+ */
Code Review / linux-2.6.git / blobdiff