SM6FBQ / HackRF clone - History

HackRF One: AC couple CLKIN

We've always specified that CLKIN should be DC (based on the Si5351C
documentation), but it has worked with AC input. AC coupling the buffer
input restores this undocumented feature.

HackRF One: add resistance to amplifier supplies

This may improve reliability since switching to a MOSFET with lower on
resistance.

HackRF One: chain SGPIO_CLK and GCK2 buffers

This more closely emulates the clock phase relationships on prior
hardware revisions that used the Si5351C.

Update clock trace widths.

HackRF One: change CLKIN_DETECT pin

- move CLKIN_DETECT to U23 pin 15, P4_8, CTIN_5
- move SGPIO13 to U23 pin 91, P2_5, GPIO5[5]
- rename SGPIO13 to TRIGGER_EN

This allows TIMER1/TIMER2 instead of TIMER3/TIMER0 to be used for CLKIN
detection, avoiding conflicts with PortaPack firmware.

SGPIO13 was never used for SGPIO, so it is renamed to reflect current
usage.

HackRF One: swap pins for platform detection

- move EN_1V8 to P5_0, U23 pin 37
- move !VAA_ENABLE to P6_10, U23 pin 100
- move !RX_AMP_PWR back to P2_12, U23 pin 106

Platform detection is now performed using P5_0 and P6_10 which avoids
the complication of having to detect a pull-up to VAA which may not yet
be switched on.