SX280HS / SX275HS / SX270HS notes

CHDK is a hack, use at your own risk!

Additionally, Digic 6 has significant differences from previously 
supported models, which means some features are not fully implemented
and the risk of unforeseen side effects is higher than ports for
previous Digic versions.

Firmware version information can be obtained using the VER.REQ method,
or by using ACID / STICK / exiftool or the firminfo Canon Basic script.


General camera and CHDK port information

- Default ALT button is the PLAYBACK button. VIDEO and DISP may also be used

- The half press zebra shortcut button is MENU

- The RAW shortcut (and generic shortcut) button is DISP

- To start in shooting mode, hold down the ON/OFF button

- Only simple_movie_status is implemented, so features or scripts that rely on
  direct access to the movie_status variable do not work

- Video bitrate can be adjusted (CBR, VBR). Maximum possible video bitrate is approx. 35000 kbit/s

- Video time based limits are raised to 3 hours (only makes sense on external power)

- Using CHDK started via the "firmware update" method has not been fully tested.
  Report any problems in the porting thread.

- GPS data in DNGs is supported on SX280. Full CHDK GPS support is not implemented.

- Canon has ceased providing updated AGPS data for the SX280. CHDK provides a replacement URL,
  http://epodownload.mediatek.com/EPO.DAT
  The AGPS updater in Canon menu will use the replacement URL when CHDK is running.

- Porting thread: https://chdk.setepontos.com/index.php?topic=11550

Issues

- Exposure overrides (and custom auto ISO) will not work correctly when
  - "AF frame" is set to "tracking AF" in Canon menu
  - "Servo AF" is enabled in Canon menu
  - "I-contrast" is enabled in Canon menu

- CHDK overlay drawing is slow, Canon display updates make the CHDK OSD blink
- PTP remote shoot can misbehave in certain shooting modes (sports mode, high speed burst mode, ...):
  when using continuous shooting (rs -cont or rs -quick in chdkptp), the number of actual shots
  may be larger than the requested number, the last shot from such a series may end up on card