Syscall index: 0x0EA7
Function signature: void TestMode(int vram)
Opens an hidden OS menu, the Test Mode, where some OS functionality can be tested and a look into the OS internals can be taken.
- vram - Whether to restore the previous VRAM when exiting the Test Mode.
- MCS browser ("Valiable Manager" (sic));
- Memory viewer (but not editor) (F4 and F5 in the "Valiable Manager");
- Font and character code checking, including for "GB codes" (Chinese codes plus alternatives to some Latin ones), probably a reference to the GB 18030 codepage;
- Setup visualizer (opens a menu like the ones seen when pressing Shift+Menu in different built-in apps, but showing all possible settings);
- Function key bitmap visualizer;
- Ability to set function key label color and screen frame color;
- Fugue FAT File System and Bfile testing functions;
- Memory usage visualizer for the heap, the main process stack and the child stack;
- Disabled function to dump flash data over USB.
Some of this functionality is present and extended in Simon Lothar's Insight add-in.
How to access
Besides calling the corresponding syscall (something the Insight add-in lets one do), there's also the key combination used for entering the diagnostics mode: on the "Delete all data" screen (which doesn't delete anything), one can quickly type 5963 to open the Test Mode. So the key combination becomes as follows:
[OPTN]+[EXP]+[AC/ON], then quickly type 5963.
More key combinations can be found here.