xmos / lib_agc Goto Github PK

The gain value, as defined in agc_channel_state_t, doesn't correspond to a gain (in dB value) on the input signal.

For example, with channel state gain set to 6, and gain_exp set to 0 (see agc_init_channel()) a constant input signal results in the following constant output values:

G(INT_MAX * 0.1) = INT_MAX * 0.54
G(INT_MAX * 0.2) = INT_MAX * 0.73
G(INT_MAX * 0.25) = INT_MAX * 0.77
G(INT_MAX * 0.4) = INT_MAX * 0.83

This is unexpected. Shouldn't the gain value in agc_channel_state_t correspond to a dB gain on the channel input?

Recent CI runs of the develop branch show a failure when running flake8, which checks Python scripts for good style. Currently we pin flake8 at v3.8.3. Flake8 uses importlib-metadata. A known issue in importlib-metadata breaks flake8. By pinning importlib-metadata at v4.13.0, flake8 can run as normal.

In passing, this issue also covers an update of the XMOS Jenkins Shared Library to the latest available version, v0.20.0.

{uint32_t, int} subtract(uint32_t a, int a_exp, uint32_t b, int b_exp), as defined in agc.xc, returns wildly incorrect values in cases where:

• is_greater_than(a, a_exp, b, b_exp) is true
• (a_exp - b_exp) < 0

Or, conversely, when:

• is_greater_than(a, a_exp, b, b_exp) is false
• (b_exp - a_exp) < 0

The EWMA alpha value for the weighted average of the correlation factor uses a 'magic number' rather than a defined constant.

This should be defined as a hash define alongside the other EWMA alpha values used in the AGC block.

agc_init_channel() sets the agc state to the following values:

db: 20
gain exp: 3
gain: 20971522

This scrambles the output of the agc process.

This repository does not contain an application note providing an example to support a customer in becoming familiar with building and using it.

The API header files include xccompat.h and use its macros to accommodate both a C and XC interface. However, only an XC definition of each declared API function exists.

The set and get functions in agc.h do not check ch_index parameter for correctness.

If ch_index >= AGC_INPUT_CHANNELS then an out-of-bounds exception will occur.

Any fix should be documented in the setter/getter Doxygen comments as defined behaviour.

The AGC API includes XC language features, specifically the use of references..

The branch feature/c_callable contains initial enhancements to provide a C API. Pull request #120 exists to review and merge these enhancements. The changes in this PR do not include the C language definitions of the AGC functions, only their declarations.