TX Power Control issues

[terrillmoore]

Per @Cyberman74

For me it seems LMiC code in radio.c selecting the PA Output pin of SX1276 is erroneous. Always Pin PA_BOOST is selected. This can cause malfunction, if board hardware does not wire this pin, because it uses the RFO_HF / RFO_LF pins only.

Code review and checking datasheet says that current code does not actually activate high-power on PA_BOOST. It always sets RegPaDac bits 2:0 to 4. Datasheet says that to activate high-power on PA_BOOST, RegPaDac bits 2:0 must be set to 7.

However, bit 7 of RegPaConfig is always set to 1, so the output port is always the PA_BOOST at +17dBm (section 5.4.3).

There are a number of constraints on duty cycle, etc., in section 5.4.3 when using +20 dBm mode.

See also #50 (just simple errors in power-setting code).

More entries are needed in the lmic_pinmap structure to specify the board configuration re LF/HF/PA_BOOST pins of the radio. This should be combined with the SPI setting changes for #37.

For additional background see mcci-catena/ibm-lmic#15 and matthijskooijman#33.

[terrillmoore]

Based on input from #300, and review of the Semtech reference code, and review of datasheets, I have a patch that addresses this for the 1272 and 1276. See 49b495d and successors.