Nintendo 1504166 Programming Manual - Page 21

AGB Programming Manual AGB Memory 3.3 Game Pak Memory Wait Control Although the 32 MB Game Pak memory space is mapped to the area from 08000000h onward, the 32 MB spaces beginning from 0A000000h and 0C000000h are images of the 32 MB space that starts at 08000000h. These images enable memory to be used according to the access speed of the Game Pak memory (1-4 wait cycles). Address Register 204h WAITCNT 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 Attributes R/W Initial Value 0000h PHI Terminal Output Control 00: No Output 01: 4.19 MHz clock 10: 8.38 MHz clock 11: 16.76 MHZ clock Prefetch Buffer Flag 0: Disabled 1: Enabled Game Pak Type Flag Game Pak RAM Wait Control Wait State 0 Wait Control Wait State 1 Wait Control Wait State 2 Wait Control WAITCNT [d15] Game Pak Type Flag The System ROM uses this. WAITCNT [d14] Prefetch Buffer Flag When the Prefetch Buffer Flag is enabled and there is some free space, the Prefetch Buffer takes control of the Game Pak Bus during the time when the CPU is not using it, and reads Game Pak ROM data repeatedly. When the CPU tries to read instructions from the Game Pak and if it hits the Prefetch Buffer, the fetch is completed with no wait in respect to the CPU. If there is no hit, the fetch is done from the Game Pak ROM and there is a wait based on the set wait state. ©1999 - 2001 Nintendo of America Inc. 21 D.C.N. AGB-06-0001-002B4