.g3a files are software add-ins for the Casio Prizm. Files of this format contain a 0x7000-byte header (28 KiB), and a code/data section that can be up to 1 MB large in OS 1.01 and 1.02. The maximum size of the code/data section in newer OSes is unknown, but it seems to be larger. Checksums are used to check whether add-ins are valid. If a part of the header isn’t documented here, it’s most likely supposed to be filled with 00.

File format #

The overall file format is similar to those used by other Casio calculators, such as the g1a file used by the fx-9860G. mkg3a implements packing of data into G3A files and can be used as an example to better understand the format.

Identification/security bytes, checksums, name #

0x0000 #

AA AC BD AF 90 88 9A 8D D3 FF FE FF FE FF. These bytes are found in almost every Prizm file, with the exception of the ninth byte (D3), which is the file type byte. If the header is inverted (xor with FF), the first eight bytes read “USBPower”.

0x000E #

The low byte of the inverse file size (at memory location 0x0013) minus 0x41. The actual Prizm OS doesn’t care about this byte, but Manager PLUS and possibly other programs do care, so it’s important to set this byte correctly even though the add-in can be run if it’s incorrect.

0x000F #

This byte is always 0xFE.

0x0010 #

Inverse filesize (four bytes). For example, if a file size is 00 0B 8A A8 you would xor it with FF FF FF FF, thus setting all 1’s to 0’s and 0’s to 1’s, and get FF F4 75 57.

0x0014 #

The low byte of the inverse file size (at memory location 0x0013) minus 0xB8. The actual Prizm OS doesn’t care about this byte, but Manager PLUS and possibly other programs do care, so it’s important to set this byte correctly even though the add-in can be run if it’s incorrect.

0x0016 #

The word sum of 8 words (16 bytes) starting at 0x7100, inverted.

0x0020 #

A simple checksum (4 bytes long) is stored here. The checksum is calculated based on the entire file, except for this checksum and the copy of this checksum at the end of the file.

0x0024 #

These two bytes are always 01 01.

0x002E #

Size of executable code section (32-bit), minus the header size. This means that if this is equal to 000001F8, the copy of the 0x0020 checksum is at 0x000071F8.

0x0040 #

Name of add-in. This is in English, but it’s not always the same as the name at 0x006B (Picture Plot is named PictPlot at 0x0040). Probably a shorter version of the name.

0x005C #

Size of entire file (32-bit).

0x0060 #

Internal name. Only the uppercase letters A-Z and the @ character seem to be used. @ is always written before the name. There’s probably a character limit of eight characters (including the @). Examples: @CONV (Conversion), @GEOM (Geometry), @PICTPLT (Picture Plot)

Localized names, version information #

0x006B #

Name of add-in (English).

0x0083 #

Name of add-in (Spanish).

0x009B #

Name of add-in (German).

0x00B3 #

Name of add-in (French).

0x00CB #

Name of add-in (Portuguese).

0x00E3 #

Name of add-in (Chinese).

The font used for Chinese displays Latin letters differently than the other languages. When making an add-in, it’s a good idea to check that the name shows up correctly when using Chinese. Long names may take up more space than the icon does, making the names of add-ins overlap.

0x00FB #

Name of add-in, probably reserved for future languages. Set to the same value as English by default.

0x0113 #

Name of add-in, probably reserved for future languages. Set to the same value as English by default.

0x012B #

Set to 0x01 for add-ins with eActivity strips, otherwise set to 0x00.

0x0130 #

Version number string. Format: XX.XX.XXXX

0x013C #

Date/time created string. Format: YYYY.MMDD.HHMM

eActivity #

This area of the add-in header describes what the add-in will look like when viewed from an eActivity. If the add-in doesn’t support eActivites, these parts of the header should all be set to 00.

0x0170 #

eActivity name of add-in (English).

0x0194 #

eActivity name of add-in (Spanish).

0x01B8 #

eActivity name of add-in (German).

0x01DC #

eActivity name of add-in (French).

0x0200 #

eActivity name of add-in (Portuguese).

0x0224 #

eActivity name of add-in (Chinese).

0x0248 #

eActivity name of add-in, probably reserved for future languages. Set to the same value as English by default.

0x026C #

eActivity name of add-in, probably reserved for future languages. Set to the same value as English by default.

0x0290 #

eActivity strip icon. The icon is 64x24 pixels large, with each pixel represented by one nibble. This means that the icon is 0x0300 bytes long (ends at 0x058F). Values from 0 to 7 can be used to produce the 8 supported colors. If a value between 8 and F is used, the pixel is displayed as black. (0 should be used if black is desired, though.)

File name, icons, executable code, checksum #

0x0EBC #

File name (including the .g3a extension).

0x1000 #

Icon that is displayed when the add-in is unselected. The icon is 92x64 pixels large, and each pixel has 16 bits of color information (5 red bits, 6 green bits, and 5 blue bits). This means that the icon is 0x2E00 bytes long (ends at 0x3DFF).

0x4000 #

Icon that is displayed when the add-in is selected. The icon is 92x64 pixels large, and each pixel has 16 bits of color information (5 red bits, 6 green bits, and 5 blue bits). This means that the icon is 0x2E00 bytes long (ends at 0x6DFF).

0x7000 #

Executable code section. This section will be mapped to virtual memory at 0x00300000 and executed when the user launches the add-in.

0x???? #

Copy of the 0x0020 checksum. These are the last four bytes of the file. The location of these four bytes can be found by adding 0x7000 to the value at 0x002E.

This page was copied from the .g3a files page on PrizmWiki before PrizmWiki was closed.