Medaka (Casio Pro Trek Smart WSD-F21HR) is a humongous watch with a secondary, sunlight readable display. The current port is good enough for daily use, but GPS doesn't work. The watch requires disassembly to flash.

This is not the Casio WSD-F20. That is a different watch, see Koi/Ayu.

Description

medaka — Casio WSD-F21HR
Status	supported
Stars
Status details
Display	good
Touch	good
Bluetooth	good
Haptics	good
Tilt to wake	good
Light sensor	missing
Always-on display	good
Dual display	partial
Microphone	unknown
Speaker	missing
Compass	good
Steps	good
Heart rate	good
USB	partial
WLAN	partial
GPS	bad
NFC	missing
Cellular	missing
Camera	missing
Crown	missing
Hands	missing

Medaka is the successor to the WSD-F20 which adds a heartrate sensor. Externally, medaka shares the main body and display with ayu, but has more aggressively designed panels and a more flexible strap, as well as a plastic back with a large heartrate sensor protrusion. It is possible to swap body panels and straps between ayu and medaka, but ayu straps will need to be slightly trimmed to fit with the thicker backplate of medaka. Medaka also has a redesigned second display, which now has segments for showing heartrate zone.

Medaka shares most of its internals with kingyo, and runs a modified kingyo kernel. At a low level, nearly everything is shared apart from the colour display panel (which is instead shared with koi/ayu), the secondary display and heartrate sensor (which are both unique). However, from a user's point of view, the two watches are nothing alike.

Second Display

The second display has 6 7-segment digits in the center, 6 7-segment digits at the bottom, a 23x5 pixel matrix at the top, two separator lines above and below the central large digits, a heartrate zone indicator curving around the left and a smattering of icons and text indicators everywhere else.

Getting USB

The body design is shared with Ayu. Follow guide for Ayu: getting USB.

Repair

The watches can be easily disassembled by removing 6 phillips screws on the back. The watch is sealed with a gasket, so water resistance is not compromised by disassembly. Replacement parts are available, but expensive.

Over time, it's common for these watches to develop horizontal cracks around the heartrate sensor. While this isn't a structural issue (the back panel is a layer of plastic over a metal internal frame) it may compromise water resistance. This seems to naturally happen because of some internal stresses in the plastic.

Miscellaneous hardware docs

Keys

The central key is the power button. The top and bottom keys are volume up and down respectively.

Manually getting to fastboot

Hold the top key while powering on the watch. Navigate the menu using the top key and select using the power button.

Sensors

Medaka has a blood oxygen sensor which isn't obviously labelled. This may need special effort to get working. It's likely the one labelled Ppg, though the two hrm sensors are also suspicious.

root@medaka:/home/ceres# test_sensors 
Hardware module ID: sensors
Hardware module Name: MultiSensor Module
Hardware module Author: Casio
Hardware module API version: 0x1
Hardware HAL API version: 0x3
Poll device version: 0x1030001
API VERSION 0.1 (legacy): 0x1
API VERSION 0.1: 0x65537
API VERSION 1.0: 0x16777217
API VERSION 1.1: 0x16842753
API VERSION 1.2: 0x16908289
API VERSION 1.3: 0x16973825
API VERSION 1.4: 0x17039361
Got 15 sensors
=== Sensor 0 ==
Name: Accelerometer
Vendor: Casio
Version: 0x1
Handle: 0x1
Type: 1
maxRange: 156.906402
resolution: 0.4788
power: 0.200000 mA
minDelay: 10000

=== Sensor 1 ==
Name: Magnetic field
Vendor: Casio
Version: 0x1
Handle: 0x2
Type: 2
maxRange: 4912.800292
resolution: 0.150000
power: 1.0 mA
minDelay: 20000

=== Sensor 2 ==
Name: Gyroscope
Vendor: Casio
Version: 0x1
Handle: 0x3
Type: 4
maxRange: 34.906585
resolution: 0.286233
power: 1.0 mA
minDelay: 10000

=== Sensor 3 ==
Name: Pressure
Vendor: Casio
Version: 0x1
Handle: 0x4
Type: 6
maxRange: 1110.0
resolution: 0.13122
power: 1.0 mA
minDelay: 40000

=== Sensor 4 ==
Name: Hrm1
Vendor: Casio
Version: 0x1
Handle: 0x5
Type: 65540
maxRange: 65535.0
resolution: 1.0
power: 3.0 mA
minDelay: 0

=== Sensor 5 ==
Name: Hrm2
Vendor: Casio
Version: 0x1
Handle: 0x6
Type: 65541
maxRange: 65535.0
resolution: 1.0
power: 3.0 mA
minDelay: 0

=== Sensor 6 ==
Name: Ppg
Vendor: Casio
Version: 0x1
Handle: 0x7
Type: 65572
maxRange: 65535.0
resolution: 1.0
power: 3.0 mA
minDelay: 20000

=== Sensor 7 ==
Name: Behavior
Vendor: Casio
Version: 0x1
Handle: 0x8
Type: 65537
maxRange: 65535.0
resolution: 1.0
power: 3.0 mA
minDelay: 0

=== Sensor 8 ==
Name: Step Counter
Vendor: Casio
Version: 0x1
Handle: 0x9
Type: 19
maxRange: 2000000000.0
resolution: 1.0
power: 0.19999 mA
minDelay: 0

=== Sensor 9 ==
Name: Step Detector
Vendor: Casio
Version: 0x1
Handle: 0xa
Type: 18
maxRange: 1.0
resolution: 1.0
power: 0.19999 mA
minDelay: 0

=== Sensor 10 ==
Name: Wrist Tilt Gesture
Vendor: Casio
Version: 0x1
Handle: 0xb
Type: 26
maxRange: 1.0
resolution: 1.0
power: 0.19999 mA
minDelay: 0

=== Sensor 11 ==
Name: Significant Motion
Vendor: Casio
Version: 0x1
Handle: 0xc
Type: 17
maxRange: 1.0
resolution: 1.0
power: 0.19999 mA
minDelay: -1

=== Sensor 12 ==
Name: Heart Rate
Vendor: Casio
Version: 0x1
Handle: 0xd
Type: 21
maxRange: 65535.0
resolution: 1.0
power: 3.0 mA
minDelay: 0

=== Sensor 13 ==
Name: Heart Rate Wake
Vendor: Casio
Version: 0x1
Handle: 0xe
Type: 21
maxRange: 65535.0
resolution: 1.0
power: 3.0 mA
minDelay: 0

=== Sensor 14 ==
Name: Simple Bha
Vendor: Casio
Version: 0x1
Handle: 0xf
Type: 65542
maxRange: 65535.0
resolution: 1.0
power: 3.0 mA
minDelay: 0