The block that controls the `.upload` target is unnecessarily replicated in multiple sub-board Makefiles. This was originally done because the SmartRF and the Launchpad can be programmed with the c2538-bsl script, whereas the sensortag cannot.
This commit moves the `cc2538-bsl` / `.upload` target logic to the top level cpu Makefile (`cpu/cc26xx-cc13xx/Makefile.cc26xx-cc13xx`). Board makefiles simply set the make variable `BOARD_SUPPORTS_BSL` to 1 to signal that they can be programmed by the BSL script. If `BOARD_SUPPORTS_BSL` is not equal to 1, trying to use the `.upload` target will return an error message.
For example:
```
$ make BOARD=sensortag/cc2650 cc26xx-demo.upload
using saved target 'srf06-cc26xx'
This board cannot be programmed with the ROM bootloader and therefore does not support the .upload target.
```
Bug fixes include:
- keep interrupts disabled during lpm_sleep() so that we don't
miss any interrupts we may have been expecting
- check that the pending etimer isn't already expired (and don't sleep
at all if it is)
- check that the about-to-be scheduled rtimer wakeup is neither too
far into the future nor too close into the future (or even in the
past) before actually setting the interrupt (should fix#1509); If
the time is out of bounds we use a default min or max value instead.
- Correctly handle LPM_MODE_MAX_SUPPORTED set to zero (and added a
macro for the zero value) so that sleeping can be disabled altogether
- If no etimer is set, we specify a wakeup time which is reasonably far
into the future instead of setting none at all (this will save on
power consumption whenever no etimers are set).
Also did a bit of refactoring in that some long functions were broken
into multiple functions.
When sending a command to the CC13xx/CC25xx RF core, we wait for command completion by checking the LSB of CMDSTA (correctly so). However, in doing so we also zero out the 3 CMDSTA return bytes. For some commands, those bytes contain useful information (e.g. an RSSI value) and are required by the caller.
This problem manifests itself e.g. in PROP mode `channel_clear()`, whereby the caller will always see an RSSI value of 0.
This pull therefore fixes the logic in `rf_core_send_cmd()` to check for command completion by blocking on the CMDSTA result byte without zeroing out the 3 return bytes.
Fixes#1465
