The CC13xx/CC26xx Sub-GHz driver header file defined several constants
that were not used in the driver.

Other constants could be replaced with generic constants which were
introduced in the prior commit.

This change removes and/or replaces redundant definitions.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

The low-level configuration of the chip's radio commands was mostly
redundant. This change removes redundant configuration code.

This is also relevant as a preparation to supporting further frequency
bands and operating modes on the same SUN FSK channel page with
similar but slightly different settings (center frequencies, channel
spacing, modulation index as defined in the standard). The SUN FSK
standard defines plenty of such variations with different physical
characteristics and trade-offs. Such variations are highly relevant in
industrial applications which will be targeted by TSCH. Using the
correct settings is required for additional features (e.g. frequency
hopping) and interoperability.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

The channel-to-frequency conversion had unreachable code which is
removed in this change.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

The driver contained references to KConfig variables w/o the required
CONFIG_ prefix. This change introduces the missing prefixes.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

This change introduces standard variable names used elsewhere in the
stack for improved naming consistency and readability.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

The CC13xx/CC26xx Sub-GHz driver announces a hardware CSMA/CA capability
which it provides only partially. This change documents the gap.

The change also fixes two related issues with the current CCA
implementation:

- The given default ED threshold was above the allowed threshold
  defined in the specification.

- The CCA timeout was not calculated according to the requirements
  defined in the standard.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

This change introduces inline documentation with references to the
current version of the IEEE 802.15.4 standard.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

The driver's CCA method had various issues and would always return an
error code. This is fixed in this change.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

Switch the driver to the soft CSMA/CA algorithm as an intermediate
compromise for improved standard compliance (namely expontential
backoff) until true hardware support can be implemented by chaining
radio commands.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

The CMD_CLEAR_RX and CMD_SET_TX_POWER commands are declared and
initialized but not used anywhere. They are therefore removed to reduce
RAM/flash footprint.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

The call to radio_api->set_channel() must not switch on RX if it was
previously off.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

The length field in the header refers to the size of the MAC so it
shouldn't rely on constants describing PHY header length. While
currently both constants have the same value this will no longer be true
for enhanced PHYs and/or MAC frames as the number of FCS bytes may then
be four.

Also introduces an assertion that ensures that the given package buffer
does not exceed the TX buffer's length. An assertion is enough as the
package buffer is allocated at compile time.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

The radio API should indicate errors when the interface is started.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

PHY overrides have been checked against the latest version of TI's
SmartRF(TM) Studio. The result was regression tested (PER/performance)
against LAUNCHXL-CC1352P1 boards.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

A known issue exists that does not allow a CC13/26x2R device to
establish a link to a CC13/26x2P device unless the capacitor array is
tuned to a non-default value in the P device.

See SimpleLink(TM) cc13xx_cc26xx SDK 6.20+ Release Notes, Known Issues.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

The antenna MUX configuration should explicitly define PULL states as
giving no value will leave the GPIO register in an unspecified state.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>