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## Glossary

B:
  - BG - A BG is one of the four layers in the GBA tiled modes. There are ham_bg[0]-ham_bg[3], which can be assigned tilesets and maps. See BG Mode Control Functions
  - BGMode - The GBAs main switch for how the display should behave. There are tiled and bitmapped BGModes. The accepted values are 0-5. 0-2 are tiled modes, 3-5 are bitmapped modes. See BG Mode Control Functions
  - Bitmap mode - A GBA display mode that does not use Tiles , but instead allows you to access each pixel in the display separately. These modes have no Map. Bitmap BG Modes are 3-5. See BG Mode Control Functions
  - Buffer - A section of memory holding information, usually about graphics or sound. In the GBA's Mode 4, you have 2 display buffers so you can write new graphics to the one buffer while you display the other one. See Bitmap Mode Functions

C:
  - CBB - Character Base Block. One of four 16kbyte blocks of the BG Video RAM. Usually the spot where you put your tile data.

D:
  - Direct Sound - The GBA's digital sound generation circuit. Allows two channels of digital 8 bit sound

H:
  - HAM - A cool development kit :)
  - HBL (aka Horizontal blank) - This is what happens every time the display refresh of the GBA reaches the end of a horizontal line and "returns" to the left to draw the next line. The time until the next line starts drawing is the HBL time. You can use this time to update your display without causing any noticable flicker, for example. See Interrupt Service Functions

I:
  - Interrupt - A facility in the GBA that allows to temporarily stop the execution of the program, and do something else. After this has ended, return to running the main program. There are multiple Interrupts, suchas the VBL interrupt, that will execute a specific function every beginning of a frame.

K:
  - Krawall - an extremely cool sound library now included in HAM. See http://mind.riot.org for ordering details for the registered version. Also see Krawall Notes

M:
  - Map - An array of numbers and attributes that tell the GBA system (in Tiled mode) where to put which tile. A map is organized in lines, and has one index for each 8*8 tile, so if your screen is 256*256, you will have a map that has info for 32*32 locations.

O:
  - OBJ - GBA specific name for sprite
  - OAM - The memory region that stores attributes about OBJ (sprites). Basically, the position and other parameters related to OBJ are saved in this region. You should only write to this region in a VBL or HBL Interrupt.

P:
  - Palette - a number of consecutive pieces of memory in the GBA that stores color values. These values are stored in BGR format, and 5 bits wide each. This means you can mix a palette color using 32 shades of blue, green and red, resulting in a total of 32768 colors to choose from. The GBA has two palettes, onr 256 color palette for BG graphics, and one for Sprite graphics. Note you can also run in 16 color mode, meaning you can assign a tile/sprite to one of 16 available palettes.

S:
  - Sprite - General computing term for a hardware assisted movable graphics rectangle usually with transparency support. Known in the GBA as OBJ.

T:
  - Tiled mode - This is a popular graphics display BGmode on the GBA. Instead of saving a bitmap of the whole screen, the screen is "tiled" into 8*8 bug graphics chunks, which can be reused. The Map tells the GBA where to put which tile. The BGModes which work in tiled mode are 0-2.
  - Tileset - A set of 8*8 graphics blocks that needs to be linked to a ham_bg . The map for this tileset must also be linked to the ham_bg.

V:
  - VBL - Vertical blank. This is the moment when the GBA starts to render a new picture at the very top left corner. A VBL happens 59.727 times / sec.

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