This tool is designed to patch the Data Frog SF2000 bisrv.asd firmware file to provide a more accurate battery level representation when operating on the stock 18650 Li-Ion battery.
A web-based tool to fix the Battery Meter is now available here: https://dteyn.github.io/sf2000/tools/batteryMeterFix.htm
The web-based tool is based on @VonMillhausen's Boot Logo Changer tool. Thank you Von Millhausen!
This Python script allows users to:
- Define Desired Voltage Levels: Easily set the desired voltage values for each of the five battery levels by modifying the VOLTAGE_LEVELS dictionary.
- Automatically Convert Voltages: The script will convert the user-defined voltage levels to the appropriate firmware values using a 50x multiplier.
- Perform a Sanity Check: Before patching, the script checks if the firmware matches the expected "08.03" version by comparing certain values at specific offsets.
- Patch the Firmware: The script will patch the
bisrv.asdfirmware file with the new battery values. - Recalculate CRC32: After patching, the script recalculates the CRC32 to ensure firmware integrity.
- Download the main.py file
- Place SF2000 firmware next to the main.py file. File should be named
bisrv-08_03.asd - Edit the script to modify the
VOLTAGE_LEVELSas needed - Run the script
The Data Frog SF2000 operates on a 1500mAh 18650 Li-Ion battery, which has certain characteristics that the firmware's original battery discharge curve does not account for. Specifically:
- The stock battery exhibits a pronounced drop-off in voltage when it reaches around 3.65v.
- The original firmware's battery discharge curve is designed to reach zero charge at 3.22v.
Given these characteristics, the original battery discharge curve can lead to inaccuracies in the battery meter.
The firmware represents battery levels using specific values that correspond to voltage readings provided by the SAR ADC driver. When the value is above a given threshold, the # of bars displayed changes accordingly.
There are five battery levels defined which correspond to how many bars are shown on the battery meter.
0xBF - 5 bars - green, full charge
0xB7 - 4 bars - green
0xAF - 3 bars - green
0xA9 - 2 bars - yellow
0xA1 - 1 bar - red, nearly empty
Any reading below the lowest value will display a 'low battery - charge soon' warning message which will interrupt gameplay and give the user a chance to save the game before the battery dies completely.
The values above correspond to actual voltage readings by multiplying the actual voltage by a factor of 50. For instance, a decimal value of 191 (0xBF) in the firmware corresponds to a voltage of 3.82V (191/50 = 3.82).
The firmware uses five distinct values to represent battery levels, ranging from "5 bars" (full charge) to "1 bar" (near empty). If the voltage reads less than the value corresponding to "1 bar", the device triggers a "low battery warning" on the screen.
The stock battery used in the device has a distinct characteristic: it exhibits a sudden and sharp drop-off in voltage when it reaches around 3.65V. This means that once the battery voltage approaches this threshold, the device can suddenly lose power and turn off.
Let's break down the stock values provided in the firmware:
0xBF - 191 - 3.82v
0xB7 - 183 - 3.66v
0xAF - 175 - 3.50v
0xA9 - 169 - 3.38v
0xA1 - 161 - 3.22v
From the table above, we can see that the firmware's stock values are set such that the battery level drops linearly. However, the second value (3.66V) is dangerously close to the battery's cutoff voltage of 3.65V. This means that when the device reads the battery level as being at the second value (4/5 bars), the battery is on the brink of its sharp drop-off, and the device can shut down unexpectedly soon after.
To address this problem, we adjusted the battery discharge curve in the firmware to better match the behavior of the stock battery. Instead of the linear drop, we introduced a curve that accounts for the battery's sharp drop-off at 3.65V.
By doing so, we ensure that the battery meter provides a more accurate representation of the remaining battery life, giving users a better indication of when their device might shut down and preventing unexpected power losses.
5 bars - 0xC8 - 200 - 4.0v
4 bars - 0xC2 - 194 - 3.88v
3 bars - 0xBE - 190 - 3.80v
2 bars - 0xBA - 186 - 3.72v
1 bar - 0xB7 - 183 - 3.66v
Below are the offsets for all known firmware versions as of August 28, 2023.
Thank you to @VonMillhausen for compiling this list and to @bnister for the core research & data:
0xBF 0xB7 0xAF 0xA9 0xA1
Mid-March: 0x35A8F8 0x35A900 0x35A9B0 0x35A9B8 0x35A9D4
April 20th: 0x35A954 0x35A95C 0x35AA0C 0x35AA14 0x35AA30
May 15th: 0x35C78C 0x35C794 0x35C844 0x35C84C 0x35C868
May 22nd: 0x35C790 0x35C798 0x35C848 0x35C850 0x35C86C
August 3rd: 0x3564EC 0x3564F4 0x35658C 0x356594 0x3565B0
Thank you to @bnister on the Retro Handhelds Discord server for the bulk of the research on this. Without their help, this fix would not have been possible. Also, the CRC32 calculation code was provided by @bnister as well.
Thank you to @VonMillhausen for their excellent SF2000 information repository which can be found here: https://github.com/vonmillhausen/sf2000