Nintendo GAME BOY ADVANCE Programming Manual page 125

May 25, 2005
12.3.5 Display Synchronization DMA
This function is used to transfer f rame data from peripheral equipment, such as a camera, to a frame buffer
in BG mode 3. Since BG mode 3 has only one frame buffer, this function is designed so that the next frame
data transfer will not overwrite the current screen data that is displayed.
When transferring one (1) frame of data composed of 240 x 160 pixels with 32,768 colors (16-bit/pixel),
use the following settings:
• Word count register
Word count The number of transfers per horizontal line
(For 32-bit DMA transfer, set to 78h).
• DMA control register
DMA repeat :1
You can enable this DMA anytime. Set the DMA enable flag to 1 after making the above settings. If the
DMA enable flag is 1 when the V count value is 162, DMA transfers will be executed in the next frame.
Synchronizing with the horizontal line, DMA, which transfers the "word count" data per horizontal line, will
be executed 160 times, from line 2 to line 161.
Data is always DMA transferred to the frame buffer address located 2 horizontal lines before the line being
drawn, so currently displayed graphics will never be affected by transferred data. When the V count value
becomes 162, the DMA enable flag is reset to 0 automatically and the DMA stops.
If the DMA enable flag is cleared manually, there is a possibility of a malfunction. Always wait until the DMA
enable flag is reset to 0.
Although the DMA repeat flag is ON, this DMA will be disabled after the transfer of 1 frame's worth of data.
Therefore, it is necessary to re-enable the DMA enable flag for every frame to be transferred.
© 1999-2005 NINTENDO
DMA 3
103
AGB-06-0001-002-B13
Released: May 27, 2005