future considerations: cleanup, shorten

Author: PeterKietzmann

doc/memos/rdm-draft-alamos-ieee802154-radio-hal.md

@@ -848,59 +848,47 @@ typedef enum {
 A 802.15.4 HAL implementation MUST indicate all capabilities supported by the
 device and driver implementation.
 
-# 7 Future proof considerations
-
-The Radio HAL is designed to be agnostic to the 802.15.4 MAC version on top.
-However, it is important to mention that most radio devices are optimized for a
-single version of the standard. In practice, hardware accelerations are usually
-not interchangeable between different versions of 802.15.4. As an example,
-devices that support frame retransmissions for IEEE802.15.4 2006 don't support
-Enhanced Beacons required by the TSCH layer of the 2012 standard.
-
-In order to implement future versions of the 802.15.4 standard, the radio HAL
-adapts some principles defined in the following sections
-
-## Transmission modes
-
-The HAL defines three transmission modes:
-- Direct transmission: the packet is sent immediately, without CCA or CSMA-CA
-- CCA transmission: the packet is sent using CCA
-- CSMA-CA transmission: the packet is sent using CSMA-CA
-
-The "transmit" function provides a "mode" argument to specify which
-transmission mode should be used.
-
-A HAL implementation can implement several TX modes, but MUST implement at
-least one.
-
-It is recommended that a HAL implements the TX mode that fits best the internal
-capabilities. However, implementing "Direct Transmission" mode is desired for
-certain modes of the 802.15.4 MAC (slotted operation) or versions beyond the
-capabilities of the hardware.
-
-As an example, radios that support frame retransmissions with CSMA-CA for
-IEEE802.15.4 2006 frames would benefit from a "CSMA-CA transmission" mode.
-However, a "Direct Transmission" implementation would be required to support
-TSCH (2012 standard) in those radios.
-
-## PHY definition
-
-PHY definitions are specific to a 802.15.4 version. Older standards use to
-define PHY channels with a channel number. In modern standards, channels are
-defined using a (`channel number`, `channel page` and `channel modulation`)
-tuple.
-
-The `config_phy` function receives a pointer to a `ieee802154_phy_conf_t`
-structure that describes the PHY configuration.  The proposed structure is
-compliant with the 2012 standard. In order to support the 2015 standard, a
-channel modulation member can be added at any time without breaking the Radio
-HAL API.
-
-## Functionalities specific to modern standards
-
-The Radio HAL ops can be extended to support certain functionalities present in
-newer standards, such as Listen Before Talk (supported by SubGHz radios).
-
+# 7 Future Proof Considerations
+
+The Radio HAL is designed to be agnostic to different versions of the
+IEEE802.15.4 standard.  A single radio device typically implements hardware
+acceleration for only one standard, whereas different standards are not always
+compatible. As an example, IEEE802.15.4--2006 devices do not support Enhanced
+Acknowledgement packets which are required by the TSCH layer of
+IEEE802.15.4--2012.  For compatibility, a software MAC can provide such
+functionality. The Radio HAL adapts considerations to enable different versions
+of the IEEE802.15.4 MAC on top of the abstraction layer.
+
+### Transmission Modes
+
+The Radio HAL interface defines three transmission modes to allow sending
+frames using (i) CSMA-CA, (ii) CCA, or (iii) directly without any protection.
+In that way, a MAC layer can easily send data frames benefiting from hardware
+accelerated CSMA-CA or Beacons that have to meet timing constraints and thus,
+require a direct send function.
+
+A HAL implementation can provide several transmit modes, but it MUST implement
+at least one. It is recommended that the implementation provides modes that
+exploit the internal devices capabilities. Implementing a direct mode is
+desired for software MAC layers on top.
+
+### PHY Definition
+
+PHY definitions are specific to a IEEE802.15.4 version. As an example, older
+standards define PHY channels with a `channel number`. In modern standards,
+channels are represented using a (`channel number`, `channel page`, `channel
+modulation`) tuple. The `config_phy` function is called with a pointer to a
+`ieee802154_phy_conf_t` structure which describes the PHY configuration. In
+order to support newer versions, this structure can be extended without braking
+the Radio HAL.
+
+### Future Radio Operations
+
+The Radio Operations interface `radio_ops` can be extended to support
+functionalities of newer standards. As an example, most SubGHz radios support a
+Listen Before Talk feature that can be implemented as a new and optional
+operation
+.
 # 8 Acknowledgements
 
 Thanks to Peter Kietzmann, Leandro Lanzieri and Martine Lenders for their