cluster_to_sector.asm

ADI BF DSP的CF卡的读写源码

/************************************************************************************************/
/*	This routine converts the given cluster number (expected in R0) into a sector number and	*/
/*	stores it in R5.																			*/
/*															  Last Modified 02-26-03.  H. Desai */
/************************************************************************************************/

.GLOBAL Cluster_to_Sector;
.EXTERN Parameters;
.SECTION program;

/**Calc. Start Sector from MP3 Start Cluster**/
/**FirstSector0fCluster = ((N-2) * SectorsPerCluster) + FirstDataSector**/
Cluster_to_Sector:
R0 += -2;
P0.H = Parameters;
P0.L = Parameters;
R1 = [P0+0x14];						//Sectors per Cluster
R2 = [P0+0x4];						//Start of Data Region 
R0 = R0.L * R1.L (IS);
R0 = R0 + R2;						//First Sector of Cluster
R1 = [P0+0xC];						//# Of Hidden Sectors
R5 = R0 + R1;

RTS;