Analog Devices ADSP-BF59x Blackfin, Hardware Reference Manual, Page: 698 / 772

Programming Examples
16-76 ADSP-BF59x Blackfin Processor Hardware Reference
In general, the block size is bigger than the size of the temporary buffer.
Therefore, the boot kernel may need to divide the processing of a single
block into multiple steps. The callback routine may also need to be
invoked multiple times—every time the temporary buffer is filled up and
once for the remaining bytes. The boot kernel passes the
dFlags
parame-
ter, so that the callback routines knows whether it is called the first time,
the last time or neither. The
dUserLong
variable in the
ADI_BOOT_DATA
structure is used to store the intermediate results between function calls.
Listing 16-7. XOR Checksum
s32 xor_callback(
ADI_BOOT_DATA* pBS,
ADI_BOOT_BUFFER* pCS,
s32 dFlags)
{
s32 i;
if ((pCS!= NULL) && (pBS->pHeader!= NULL)) {
if (dFlags & CBFLAG_FIRST) {
pBS->dUserLong = 0;
}
for (i=0; i<pCS->dByteCount/sizeof(s32); i++) {
pBS->dUserLong^= ((s32 *)pCS->pSource)[i];
}
if (dFlags & CBFLAG_FINAL) {
if (pBS->dUserLong!= pBS->pHeader->dArgument) {
idle ();
}
}
}
return 0;
}
void xor_initcode (ADI_BOOT_DATA *pBS)
{