The old gyro_lpf setting was based on the DLPF_CFG values for the MPU6050 gyro and the enumeration was inaccurate and misleading. For example, the default "OFF" setting did not disable the DLPF, but actually set it to around 250hz. The actual cutoff frequency for each setting varies by gyro hardware so the literal frequencies in the enumeration were also incorrect.
Removed gyro_lpf and replaced it with gyro_hardware_lpf (8KHz) and gyro_32khz_hardware_lpf (32KHz). The parameters were renamed to indicate that they are hardware filtering options to differentiate from the many software lowpass filtering options.
gyro_hardware_lpf - This parameter sets the filtering and sample rate options for 8KHz gyros (or 32KHz capable gyros running in 8KHz mode).
- NORMAL - default setting that is equivalent to the previous "OFF" setting. Configures 8KHz sampling with ~250Hz filter cutoff.
- EXPERIMENTAL - 8KHz sampling with a higher frequency filter cutoff (around 3000hz). Considerably more noisy and requires additional software filtering. Note that for the MPU6000 Invensense doesn't officially document the filter cutoff frequency for this selection and simply lists it as "reserved". In testing it's clear that a higher frequency filter cutoff is being selected due to the increased noise, but the actual cutoff frequency is unknown.
- 1KHZ_SAMPLING - 1KHz sample rate with and approximate 188Hz filter cutoff.
Note that the following additional 1KHz sample rate options with lower filter cutoffs have been eliminated - "98HZ", "42HZ", "20HZ", "10HZ", "5HZ". It seems unlikely that these are still needed are probably no longer viable and flight performance would be very poor.
gyro_32khz_hardware_lpf - This parameter sets the filtering options while running in 32KHz mode on capable gyros. It also exposes a new high frequency filter cutoff mode.
- NORMAL - The default and matches the current settings used for 32KHz mode. Provides a filter cutoff around 3000Hz.
- EXPERIMENTAL - Selects a filter cutoff around 8000Hz. This is a very noisy setting and will require substantial software filtering.
The default values for both 8KHz and 32KHz sample rates were chosen to match the previous defaults and users should not experience any performance differences.
Normalized the gyro initialization. Previously there was little consistency on how the initialization was performed and the settings interpreted. For example, MPU9250 used a completely different logic tree when configuring the registers.
Disconnected the literal parameter value from the gyro initialization. The gyro_lpf parameter contained a number from 0-7 that was literally applied to the configuration register during the gyro initialization. This caused some older gyro initializations to be incorrect as they used a different register layout (MPU3050 and L3G4200D). By transitioning to a logical selection the actual value applied to the hardware register is abstracted. This will better future-proof the design as new gyros may have a different register structure that may be incompatible with the old method.
Added a gyroregisters command to the CLI that is used to read the current register settings from the gyro and dump them to the CLI. This is used to verify the configuration in comparison to the datasheets for the various gyros. Testing empirically by looking at the relative noise from the gyros can give a rough estimate whether the different options are selecting correctly, but it's not very precise. The code for the gyroregisters CLI command is wrapped inside #ifdef USE_GYRO_REGISTER_DUMP blocks to allow easy disabling. It's currently enabled for all targets but we may decide to disable before release or only limit to targets with more available space (>=F4).
