[beluga] Add support for "Power Saver" mode

Power Saver mode is a special mode available on beluga where the Wear 3100 is shutdown and the Apollo3 MCU will take control of the display. In this mode the watch functions as a basic wristband where you can choose different watchfaces, track steps, and monitor the heartrate. It also has support for Bluetooth Low Energy, but for this to work you'll likely need to install "HeyTap"

Essentially the "Dual SoC" mode means that you can extend the battery greatly by turning the watch into a smart wristband.

On WearOS you can activate this mode by long pressing the accessory button.

Current research

I've tried to decompile all services on a beluga dump looking for traces to this "Power Saver" mode. This chapter will describe some of those findings.

MCU firmware

The MCU firmware is usually used for sensors and some minor other features. On beluga this firmware also can take over control of the LCD (and touch) allowing you to use the watch while it's essentially turned off (meaning the WearOS system is no longer turned on).

There are three separate firmware versions depending on the model: x19w6, x19w8 and x19w12. All of them follow a similar structure:

.
├── config.txt
├── cxd5603_19441_40eaf83_123LBGE.ebin1
├── cxd5603_19441_40eaf83_123LBGE.ebin2
├── cxd5603_19441_40eaf83_123LBGE.ebin3
├── cxd5603_19441_40eaf83_123LBGE.ebin4
├── font_2007241757_1.bin
├── font_2007241757_2.bin
├── font_2007241757_3.bin
├── font_2007241757_4.bin
├── mcu_OW19W3_X19W8_C.01_2105100104.bin
├── multiloader.bin
└── ui_2008111417.bin

These are located on the vendor partition: /firmware/mcufirmware/

The config.txt file contains the information on which file to use:

mcu:OW19W3_X19W8_C.01_2105100104 
gps:cxd5603:19441 
font:2007241757 
ui:2008111417

mcu_xx.bin

This files contains the actual firmware along with some AES keys (?). binwalk reveals the following:


DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
744794        0xB5D5A         LANCOM firmware loader, model: " SX932x_AVGLSB Fail!", loader version: "read",
780244        0xBE7D4         CRC32 polynomial table, little endian
818402        0xC7CE2         AES S-Box
818658        0xC7DE2         AES Inverse S-Box
863256        0xD2C18         AES S-Box
863512        0xD2D18         AES Inverse S-Box

It's currently not known how to reverse engineer the firmware, though, it does not appear to be encrypted in any form, since there are some readable strings available after extracting the first entry using binwalk.

ui_xx.bin

This contains all the bitmaps used to display something on the display, binwalk reveals:


DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
8704          0x2200          PC bitmap, Windows 3.x format,, 24 x 30 x 8
9400          0x24B8          PC bitmap, Windows 3.x format,, 24 x 30 x 8
9912          0x26B8          PC bitmap, Windows 3.x format,, 36 x 30 x 8
10404         0x28A4          PC bitmap, Windows 3.x format,, 36 x 30 x 8
10972         0x2ADC          PC bitmap, Windows 3.x format,, 36 x 30 x 8
11592         0x2D48          PC bitmap, Windows 3.x format,, 36 x 30 x 8
12292         0x3004          PC bitmap, Windows 3.x format,, 36 x 30 x 8
13068         0x330C          PC bitmap, Windows 3.x format,, 12 x 12 x 8
13292         0x33EC          PC bitmap, Windows 3.x format,, 12 x 12 x 8
13544         0x34E8          PC bitmap, Windows 3.x format,, 12 x 12 x 8
13768         0x35C8          PC bitmap, Windows 3.x format,, 192 x 160 x 8
15980         0x3E6C          PC bitmap, Windows 3.x format,, 192 x 160 x 8
18104         0x46B8          PC bitmap, Windows 3.x format,, 192 x 160 x 8
20572         0x505C          PC bitmap, Windows 3.x format,, 192 x 160 x 8
22884         0x5964          PC bitmap, Windows 3.x format,, 192 x 160 x 8
25124         0x6224          PC bitmap, Windows 3.x format,, 192 x 160 x 8
27436         0x6B2C          PC bitmap, Windows 3.x format,, 192 x 160 x 8
29748         0x7434          PC bitmap, Windows 3.x format,, 192 x 160 x 8
32060         0x7D3C          PC bitmap, Windows 3.x format,, 192 x 160 x 8
34372         0x8644          PC bitmap, Windows 3.x format,, 192 x 160 x 8
36684         0x8F4C          PC bitmap, Windows 3.x format,, 328 x 96 x 8
37980         0x945C          PC bitmap, Windows 3.x format,, 328 x 96 x 8
39032         0x9878          PC bitmap, Windows 3.x format,, 44 x 66 x 8
40396         0x9DCC          PC bitmap, Windows 3.x format,, 32 x 66 x 8
41152         0xA0C0          PC bitmap, Windows 3.x format,, 44 x 66 x 8
42216         0xA4E8          PC bitmap, Windows 3.x format,, 44 x 66 x 8
43336         0xA948          PC bitmap, Windows 3.x format,, 44 x 66 x 8
44264         0xACE8          PC bitmap, Windows 3.x format,, 44 x 66 x 8
45392         0xB150          PC bitmap, Windows 3.x format,, 44 x 66 x 8
46684         0xB65C          PC bitmap, Windows 3.x format,, 44 x 66 x 8
47568         0xB9D0          PC bitmap, Windows 3.x format,, 44 x 66 x 8
49056         0xBFA0          PC bitmap, Windows 3.x format,, 44 x 66 x 8
50352         0xC4B0          PC bitmap, Windows 3.x format,, 52 x 52 x 8
51228         0xC81C          PC bitmap, Windows 3.x format,, 120 x 120 x 8
53032         0xCF28          PC bitmap, Windows 3.x format,, 120 x 120 x 8
54648         0xD578          PC bitmap, Windows 3.x format,, 52 x 52 x 8
55480         0xD8B8          PC bitmap, Windows 3.x format,, 52 x 52 x 8
56612         0xDD24          PC bitmap, Windows 3.x format,, 52 x 52 x 8
57432         0xE058          PC bitmap, Windows 3.x format,, 52 x 52 x 8
58436         0xE444          PC bitmap, Windows 3.x format,, 180 x 207 x 8
61988         0xF224          PC bitmap, Windows 3.x format,, 254 x 300 x 8
66416         0x10370         PC bitmap, Windows 3.x format,, 254 x 300 x 8
70660         0x11404         PC bitmap, Windows 3.x format,, 144 x 188 x 8
73304         0x11E58         PC bitmap, Windows 3.x format,, 144 x 188 x 8
76020         0x128F4         PC bitmap, Windows 3.x format,, 144 x 188 x 8
78776         0x133B8         PC bitmap, Windows 3.x format,, 144 x 188 x 8
81616         0x13ED0         PC bitmap, Windows 3.x format,, 144 x 188 x 8
84564         0x14A54         PC bitmap, Windows 3.x format,, 144 x 188 x 8
87528         0x155E8         PC bitmap, Windows 3.x format,, 144 x 188 x 8
90440         0x16148         PC bitmap, Windows 3.x format,, 144 x 188 x 8
93372         0x16CBC         PC bitmap, Windows 3.x format,, 144 x 188 x 8
96280         0x17818         PC bitmap, Windows 3.x format,, 144 x 188 x 8
98840         0x18218         PC bitmap, Windows 3.x format,, 144 x 188 x 8
101484        0x18C6C         PC bitmap, Windows 3.x format,, 144 x 188 x 8
104188        0x196FC         PC bitmap, Windows 3.x format,, 144 x 188 x 8
106944        0x1A1C0         PC bitmap, Windows 3.x format,, 144 x 188 x 8
109784        0x1ACD8         PC bitmap, Windows 3.x format,, 144 x 188 x 8
112732        0x1B85C         PC bitmap, Windows 3.x format,, 144 x 188 x 8
115696        0x1C3F0         PC bitmap, Windows 3.x format,, 144 x 188 x 8
118608        0x1CF50         PC bitmap, Windows 3.x format,, 144 x 188 x 8
121540        0x1DAC4         PC bitmap, Windows 3.x format,, 144 x 188 x 8
124448        0x1E620         PC bitmap, Windows 3.x format,, 144 x 188 x 8
127008        0x1F020         PC bitmap, Windows 3.x format,, 220 x 180 x 8
129064        0x1F828         PC bitmap, Windows 3.x format,, 220 x 180 x 8
131304        0x200E8         PC bitmap, Windows 3.x format,, 220 x 180 x 8
133508        0x20984         PC bitmap, Windows 3.x format,, 220 x 180 x 8
135424        0x21100         PC bitmap, Windows 3.x format,, 220 x 180 x 8
137296        0x21850         PC bitmap, Windows 3.x format,, 220 x 180 x 8
139132        0x21F7C         PC bitmap, Windows 3.x format,, 220 x 180 x 8
140744        0x225C8         PC bitmap, Windows 3.x format,, 220 x 180 x 8
142356        0x22C14         PC bitmap, Windows 3.x format,, 220 x 180 x 8
144192        0x23340         PC bitmap, Windows 3.x format,, 220 x 180 x 8
146124        0x23ACC         PC bitmap, Windows 3.x format,, 120 x 146 x 8
148484        0x24404         PC bitmap, Windows 3.x format,, 120 x 146 x 8
150204        0x24ABC         PC bitmap, Windows 3.x format,, 120 x 146 x 8
152100        0x25224         PC bitmap, Windows 3.x format,, 120 x 146 x 8
154016        0x259A0         PC bitmap, Windows 3.x format,, 120 x 146 x 8
155872        0x260E0         PC bitmap, Windows 3.x format,, 120 x 146 x 8
157804        0x2686C         PC bitmap, Windows 3.x format,, 120 x 146 x 8
159848        0x27068         PC bitmap, Windows 3.x format,, 120 x 146 x 8
161456        0x276B0         PC bitmap, Windows 3.x format,, 120 x 146 x 8
163708        0x27F7C         PC bitmap, Windows 3.x format,, 120 x 146 x 8
165784        0x28798         PC bitmap, Windows 3.x format,, 120 x 146 x 8
168520        0x29248         PC bitmap, Windows 3.x format,, 120 x 146 x 8
170456        0x299D8         PC bitmap, Windows 3.x format,, 120 x 146 x 8
172732        0x2A2BC         PC bitmap, Windows 3.x format,, 120 x 146 x 8
175008        0x2ABA0         PC bitmap, Windows 3.x format,, 120 x 146 x 8
177136        0x2B3F0         PC bitmap, Windows 3.x format,, 120 x 146 x 8
179416        0x2BCD8         PC bitmap, Windows 3.x format,, 120 x 146 x 8
181808        0x2C630         PC bitmap, Windows 3.x format,, 120 x 146 x 8
183636        0x2CD54         PC bitmap, Windows 3.x format,, 120 x 146 x 8
186312        0x2D7C8         PC bitmap, Windows 3.x format,, 120 x 146 x 8
188692        0x2E114         PC bitmap, Windows 3.x format,, 220 x 268 x 8
196320        0x2FEE0         PC bitmap, Windows 3.x format,, 48 x 48 x 8
196904        0x30128         PC bitmap, Windows 3.x format,, 48 x 48 x 8
197680        0x30430         PC bitmap, Windows 3.x format,, 220 x 268 x 8
212808        0x33F48         PC bitmap, Windows 3.x format,, 126 x 172 x 8
217084        0x34FFC         PC bitmap, Windows 3.x format,, 126 x 172 x 8
221140        0x35FD4         PC bitmap, Windows 3.x format,, 126 x 172 x 8
223244        0x3680C         PC bitmap, Windows 3.x format,, 126 x 172 x 8
226496        0x374C0         PC bitmap, Windows 3.x format,, 126 x 172 x 8
231504        0x38850         PC bitmap, Windows 3.x format,, 126 x 172 x 8
236596        0x39C34         PC bitmap, Windows 3.x format,, 126 x 172 x 8
241900        0x3B0EC         PC bitmap, Windows 3.x format,, 126 x 172 x 8
245460        0x3BED4         PC bitmap, Windows 3.x format,, 126 x 172 x 8
250176        0x3D140         PC bitmap, Windows 3.x format,, 126 x 172 x 8
254796        0x3E34C         PC bitmap, Windows 3.x format,, 126 x 172 x 8
263732        0x40634         PC bitmap, Windows 3.x format,, 126 x 172 x 8
266344        0x41068         PC bitmap, Windows 3.x format,, 126 x 172 x 8
269676        0x41D6C         PC bitmap, Windows 3.x format,, 126 x 172 x 8
275912        0x435C8         PC bitmap, Windows 3.x format,, 126 x 172 x 8
280776        0x448C8         PC bitmap, Windows 3.x format,, 126 x 172 x 8
285324        0x45A8C         PC bitmap, Windows 3.x format,, 126 x 172 x 8
291308        0x471EC         PC bitmap, Windows 3.x format,, 126 x 172 x 8
296168        0x484E8         PC bitmap, Windows 3.x format,, 126 x 172 x 8
306344        0x4ACA8         PC bitmap, Windows 3.x format,, 126 x 172 x 8
313384        0x4C828         PC bitmap, Windows 3.x format,, 28 x 28 x 8
313956        0x4CA64         PC bitmap, Windows 3.x format,, 360 x 360 x 8
319228        0x4DEFC         PC bitmap, Windows 3.x format,, 220 x 268 x 8
324836        0x4F4E4         PC bitmap, Windows 3.x format,, 128 x 128 x 8
326592        0x4FBC0         PC bitmap, Windows 3.x format,, 128 x 128 x 8
329332        0x50674         PC bitmap, Windows 3.x format,, 128 x 128 x 8
331892        0x51074         PC bitmap, Windows 3.x format,, 128 x 128 x 8
334476        0x51A8C         PC bitmap, Windows 3.x format,, 128 x 128 x 8
336976        0x52450         PC bitmap, Windows 3.x format,, 128 x 128 x 8
339360        0x52DA0         PC bitmap, Windows 3.x format,, 128 x 128 x 8
341712        0x536D0         PC bitmap, Windows 3.x format,, 128 x 128 x 8
344008        0x53FC8         PC bitmap, Windows 3.x format,, 128 x 128 x 8
346220        0x5486C         PC bitmap, Windows 3.x format,, 128 x 128 x 8
348344        0x550B8         PC bitmap, Windows 3.x format,, 128 x 128 x 8
350336        0x55880         PC bitmap, Windows 3.x format,, 128 x 128 x 8
352248        0x55FF8         PC bitmap, Windows 3.x format,, 128 x 128 x 8
354064        0x56710         PC bitmap, Windows 3.x format,, 128 x 128 x 8
355652        0x56D44         PC bitmap, Windows 3.x format,, 128 x 128 x 8
357056        0x572C0         PC bitmap, Windows 3.x format,, 148 x 148 x 8
359092        0x57AB4         PC bitmap, Windows 3.x format,, 148 x 148 x 8
362316        0x5874C         PC bitmap, Windows 3.x format,, 148 x 148 x 8
365320        0x59308         PC bitmap, Windows 3.x format,, 148 x 148 x 8
368232        0x59E68         PC bitmap, Windows 3.x format,, 148 x 148 x 8
371180        0x5A9EC         PC bitmap, Windows 3.x format,, 148 x 148 x 8
374004        0x5B4F4         PC bitmap, Windows 3.x format,, 148 x 148 x 8
376788        0x5BFD4         PC bitmap, Windows 3.x format,, 148 x 148 x 8
379480        0x5CA58         PC bitmap, Windows 3.x format,, 148 x 148 x 8
382064        0x5D470         PC bitmap, Windows 3.x format,, 148 x 148 x 8
384564        0x5DE34         PC bitmap, Windows 3.x format,, 148 x 148 x 8
386920        0x5E768         PC bitmap, Windows 3.x format,, 148 x 148 x 8
389148        0x5F01C         PC bitmap, Windows 3.x format,, 148 x 148 x 8
391268        0x5F864         PC bitmap, Windows 3.x format,, 148 x 148 x 8
393088        0x5FF80         PC bitmap, Windows 3.x format,, 148 x 148 x 8
394684        0x605BC         PC bitmap, Windows 3.x format,, 194 x 194 x 8
397040        0x60EF0         PC bitmap, Windows 3.x format,, 194 x 194 x 8
400112        0x61AF0         PC bitmap, Windows 3.x format,, 194 x 194 x 8
403176        0x626E8         PC bitmap, Windows 3.x format,, 194 x 194 x 8
406124        0x6326C         PC bitmap, Windows 3.x format,, 194 x 194 x 8
408860        0x63D1C         PC bitmap, Windows 3.x format,, 194 x 194 x 8
411468        0x6474C         PC bitmap, Windows 3.x format,, 194 x 194 x 8
414000        0x65130         PC bitmap, Windows 3.x format,, 194 x 194 x 8
416428        0x65AAC         PC bitmap, Windows 3.x format,, 194 x 194 x 8
418768        0x663D0         PC bitmap, Windows 3.x format,, 194 x 194 x 8
420992        0x66C80         PC bitmap, Windows 3.x format,, 194 x 194 x 8
423096        0x674B8         PC bitmap, Windows 3.x format,, 194 x 194 x 8
425064        0x67C68         PC bitmap, Windows 3.x format,, 194 x 194 x 8
426900        0x68394         PC bitmap, Windows 3.x format,, 194 x 194 x 8
428604        0x68A3C         PC bitmap, Windows 3.x format,, 194 x 194 x 8
429976        0x68F98         PC bitmap, Windows 3.x format,, 44 x 14 x 8
430204        0x6907C         PC bitmap, Windows 3.x format,, 178 x 96 x 8
431336        0x694E8         PC bitmap, Windows 3.x format,, 220 x 268 x 8
438904        0x6B278         PC bitmap, Windows 3.x format,, 8 x 34 x 8
439316        0x6B414         PC bitmap, Windows 3.x format,, 10 x 34 x 8
439656        0x6B568         PC bitmap, Windows 3.x format,, 18 x 34 x 8
440208        0x6B790         PC bitmap, Windows 3.x format,, 17 x 34 x 8
440816        0x6B9F0         PC bitmap, Windows 3.x format,, 22 x 34 x 8
441424        0x6BC50         PC bitmap, Windows 3.x format,, 19 x 34 x 8
442008        0x6BE98         PC bitmap, Windows 3.x format,, 5 x 34 x 8
442316        0x6BFCC         PC bitmap, Windows 3.x format,, 11 x 34 x 8
442836        0x6C1D4         PC bitmap, Windows 3.x format,, 11 x 34 x 8
443360        0x6C3E0         PC bitmap, Windows 3.x format,, 13 x 34 x 8
443776        0x6C580         PC bitmap, Windows 3.x format,, 17 x 34 x 8
444168        0x6C708         PC bitmap, Windows 3.x format,, 7 x 34 x 8
444500        0x6C854         PC bitmap, Windows 3.x format,, 10 x 34 x 8
444780        0x6C96C         PC bitmap, Windows 3.x format,, 9 x 34 x 8
445080        0x6CA98         PC bitmap, Windows 3.x format,, 12 x 34 x 8
445516        0x6CC4C         PC bitmap, Windows 3.x format,, 16 x 34 x 8
446096        0x6CE90         PC bitmap, Windows 3.x format,, 16 x 34 x 8
446548        0x6D054         PC bitmap, Windows 3.x format,, 16 x 34 x 8
447032        0x6D238         PC bitmap, Windows 3.x format,, 16 x 34 x 8
447560        0x6D448         PC bitmap, Windows 3.x format,, 16 x 34 x 8
448068        0x6D644         PC bitmap, Windows 3.x format,, 16 x 34 x 8
448596        0x6D854         PC bitmap, Windows 3.x format,, 16 x 34 x 8
449132        0x6DA6C         PC bitmap, Windows 3.x format,, 16 x 34 x 8
449564        0x6DC1C         PC bitmap, Windows 3.x format,, 16 x 34 x 8
450156        0x6DE6C         PC bitmap, Windows 3.x format,, 16 x 34 x 8
450692        0x6E084         PC bitmap, Windows 3.x format,, 8 x 34 x 8
451016        0x6E1C8         PC bitmap, Windows 3.x format,, 7 x 34 x 8
451380        0x6E334         PC bitmap, Windows 3.x format,, 15 x 34 x 8
451780        0x6E4C4         PC bitmap, Windows 3.x format,, 17 x 34 x 8
452104        0x6E608         PC bitmap, Windows 3.x format,, 16 x 34 x 8
452508        0x6E79C         PC bitmap, Windows 3.x format,, 15 x 34 x 8
452976        0x6E970         PC bitmap, Windows 3.x format,, 26 x 34 x 8
453812        0x6ECB4         PC bitmap, Windows 3.x format,, 20 x 34 x 8
454376        0x6EEE8         PC bitmap, Windows 3.x format,, 19 x 34 x 8
454976        0x6F140         PC bitmap, Windows 3.x format,, 19 x 34 x 8
455524        0x6F364         PC bitmap, Windows 3.x format,, 19 x 34 x 8
456128        0x6F5C0         PC bitmap, Windows 3.x format,, 17 x 34 x 8
456596        0x6F794         PC bitmap, Windows 3.x format,, 16 x 34 x 8
457036        0x6F94C         PC bitmap, Windows 3.x format,, 20 x 34 x 8
457628        0x6FB9C         PC bitmap, Windows 3.x format,, 21 x 34 x 8
458264        0x6FE18         PC bitmap, Windows 3.x format,, 9 x 34 x 8
458744        0x6FFF8         PC bitmap, Windows 3.x format,, 17 x 34 x 8
459264        0x70200         PC bitmap, Windows 3.x format,, 19 x 34 x 8
459880        0x70468         PC bitmap, Windows 3.x format,, 16 x 34 x 8
460316        0x7061C         PC bitmap, Windows 3.x format,, 26 x 34 x 8
461104        0x70930         PC bitmap, Windows 3.x format,, 21 x 34 x 8
461804        0x70BEC         PC bitmap, Windows 3.x format,, 21 x 34 x 8
462428        0x70E5C         PC bitmap, Windows 3.x format,, 19 x 34 x 8
462964        0x71074         PC bitmap, Windows 3.x format,, 21 x 34 x 8
463624        0x71308         PC bitmap, Windows 3.x format,, 19 x 34 x 8
464248        0x71578         PC bitmap, Windows 3.x format,, 18 x 34 x 8
464808        0x717A8         PC bitmap, Windows 3.x format,, 18 x 34 x 8
465236        0x71954         PC bitmap, Windows 3.x format,, 19 x 34 x 8
465844        0x71BB4         PC bitmap, Windows 3.x format,, 19 x 34 x 8
466428        0x71DFC         PC bitmap, Windows 3.x format,, 26 x 34 x 8
467200        0x72100         PC bitmap, Windows 3.x format,, 19 x 34 x 8
467788        0x7234C         PC bitmap, Windows 3.x format,, 18 x 34 x 8
468316        0x7255C         PC bitmap, Windows 3.x format,, 18 x 34 x 8
468788        0x72734         PC bitmap, Windows 3.x format,, 8 x 34 x 8
469268        0x72914         PC bitmap, Windows 3.x format,, 13 x 34 x 8
469732        0x72AE4         PC bitmap, Windows 3.x format,, 8 x 34 x 8
470204        0x72CBC         PC bitmap, Windows 3.x format,, 13 x 34 x 8
470604        0x72E4C         PC bitmap, Windows 3.x format,, 14 x 34 x 8
470868        0x72F54         PC bitmap, Windows 3.x format,, 10 x 34 x 8
471168        0x73080         PC bitmap, Windows 3.x format,, 16 x 34 x 8
471664        0x73270         PC bitmap, Windows 3.x format,, 17 x 34 x 8
472240        0x734B0         PC bitmap, Windows 3.x format,, 16 x 34 x 8
472712        0x73688         PC bitmap, Windows 3.x format,, 16 x 34 x 8
473276        0x738BC         PC bitmap, Windows 3.x format,, 16 x 34 x 8
473752        0x73A98         PC bitmap, Windows 3.x format,, 11 x 34 x 8
474256        0x73C90         PC bitmap, Windows 3.x format,, 17 x 34 x 8
474856        0x73EE8         PC bitmap, Windows 3.x format,, 17 x 34 x 8
475436        0x7412C         PC bitmap, Windows 3.x format,, 8 x 34 x 8
475856        0x742D0         PC bitmap, Windows 3.x format,, 10 x 34 x 8
476368        0x744D0         PC bitmap, Windows 3.x format,, 16 x 34 x 8
476904        0x746E8         PC bitmap, Windows 3.x format,, 8 x 34 x 8
477348        0x748A4         PC bitmap, Windows 3.x format,, 26 x 34 x 8
478024        0x74B48         PC bitmap, Windows 3.x format,, 17 x 34 x 8
478548        0x74D54         PC bitmap, Windows 3.x format,, 17 x 34 x 8
479056        0x74F50         PC bitmap, Windows 3.x format,, 17 x 34 x 8
479624        0x75188         PC bitmap, Windows 3.x format,, 17 x 34 x 8
480200        0x753C8         PC bitmap, Windows 3.x format,, 11 x 34 x 8
480600        0x75558         PC bitmap, Windows 3.x format,, 15 x 34 x 8
481084        0x7573C         PC bitmap, Windows 3.x format,, 10 x 34 x 8
481536        0x75900         PC bitmap, Windows 3.x format,, 17 x 34 x 8
482072        0x75B18         PC bitmap, Windows 3.x format,, 15 x 34 x 8
482540        0x75CEC         PC bitmap, Windows 3.x format,, 22 x 34 x 8
483152        0x75F50         PC bitmap, Windows 3.x format,, 15 x 34 x 8
483644        0x7613C         PC bitmap, Windows 3.x format,, 15 x 34 x 8
484168        0x76348         PC bitmap, Windows 3.x format,, 15 x 34 x 8
484580        0x764E4         PC bitmap, Windows 3.x format,, 10 x 34 x 8
485096        0x766E8         PC bitmap, Windows 3.x format,, 8 x 34 x 8
485556        0x768B4         PC bitmap, Windows 3.x format,, 10 x 34 x 8
486072        0x76AB8         PC bitmap, Windows 3.x format,, 20 x 34 x 8
486452        0x76C34         PC bitmap, Windows 3.x format,, 23 x 34 x 8
487012        0x76E64         PC bitmap, Windows 3.x format,, 180 x 207 x 8
490500        0x77C04         PC bitmap, Windows 3.x format,, 48 x 48 x 8
491124        0x77E74         PC bitmap, Windows 3.x format,, 48 x 48 x 8
491596        0x7804C         PC bitmap, Windows 3.x format,, 48 x 48 x 8
492220        0x782BC         PC bitmap, Windows 3.x format,, 48 x 48 x 8

Here's a preview of some of the contents:

Screenshot from 2023-01-15 14-47-29

WearOS

Triggering this mode from WearOS doesn't appear to be trivial as it's tightly embedded in the system. There are four references to "Power Saver":

grep: system_dir/system/app/HeyHealth/HeyHealth.apk: binary file matches
grep: system_dir/system/framework/framework-res.apk: binary file matches
grep: system_dir/system/priv-app/HeySettings/HeySettings.apk: binary file matches
grep: system_dir/system/priv-app/HeySystemUIPartner/HeySystemUIPartner.apk: binary file matches

After extracting the apks it was shown HeySystemUIPartner is responsible for the UI shown when you long press the accessory button. The others didn't initially show anything of interest at this point as the goal is to find out how to trigger the "Power Saver" mode.

After further research it became obvious that an Intent named com.android.internal.intent.action.REQUEST_WRISTMODE is responsible for triggering the mode. However finding this was harder than it may seem at a first glance. But a comment to WristbandConfirmActivity revealed more information. This appears to be the Intent we need.

Log.d(ShutdownUINormal.TAG, "start WristbandConfirmActivity with user confirm");
Intent intent = new Intent("com.android.internal.intent.action.REQUEST_WRISTMODE");

This activity contains the logic to show a dialog and when confirmed it will initiate a shutdown using the Android PowerManager. But It passes a special reason flag with it ENTER_WRIST_BAND_MODE. So it ends up calling this:

((PowerManager) WristbandConfirmActivity.this.mContext.getSystemService("power")).shutdown(false, "ENTER_WRIST_BAND_MODE", false);

This call is located in (my) decompiled code: HeySystemUIPartner/sources/com/heytap/wearable/systemuipartner/wristband/WristBandConfirmActivity.java.

services.vdex contains the reference to ENTER_WRIST_BAND_MODE in the sources/com/android/server/power/ShutdownMcuThread.java file. Specifically this check:

boolean isEnterWristBandMode = this.mReason != null && this.mReason.equals("ENTER_WRIST_BAND_MODE");

Which ends up setting a targetMode. To turn off the entire system it's set to 2 to enable WristBandMode/"Power Saver" mode it's set to 1.

Then it calls setMcuWorkMode the implementation for this function is located in boot-framework.vdex. Depending on the workMode (which is the targetMode) it will set a message id:

0 -> 373
1 -> 375
2 -> 374

At this point it will send a message to the SensorHubManager: this.mSensorHubmanager.sendInfoSafely(msgId, new OppoData().setData(data));

Finally the SensorHubManager appears to be the point where data is actually send to the MCU via a binder interface to the deamonserver. On AsteroidOS this interface is also available as it is needed for sensors to work: https://github.com/AsteroidOS/meta-smartwatch/blob/59166cef96bc7e55dc6292826644a8d12c272ba0/meta-beluga/recipes-android/android-init/android-init/init.rc#L56

Data is sent to the deamonserver by using a transaction which is a call to an A Android API used specifically for the binder interface:

Parcel _data = Parcel.obtain();
_data.writeInterfaceToken(ISensorHubService.DESCRIPTOR);
_data.writeInt(bussnessID);
_data.writeInt(1);
data.writeToParcel(_data);
this.mSensorHubService.transact(1, _data, _reply, 0);

bussnessID is the message id mentioned previously.

Next steps

Create a simple application that can talk to the deamonserver using the binder interface. We already have some reference material to this by means of:

bluebinder: Bluetooth binder. Creates a simple bridge between the Bluetooth binder service and a virtual HCI device.
geoclue-hybris-plugin: Uses the binder interface for GPS.
sensorfw: Uses the sensor binder interface for sensor support.

AsteroidOS / meta-smartwatch