public int Arm(IdeRequest !ideRequest)
{
byte value = BUSMASTER_CONTROL_MASK_START;
if (ideRequest.Command == IdeCmdType.Read)
{
value |= BUSMASTER_CONTROL_MASK_WRITE;
}
commandPort.Write8(value); // enable BM
return(0);
} // BmArm
public void BmPrepareController(IdeRequest !ideRequest)
{
// Perform steps 1 and 2 above: set up PRD, clear
// error snd interrupt
// Init. Scatter Gather List Register
uint thePrd = FillPrdTable(ideRequest);
prdPort.Write32(thePrd);
// Clear Errors
byte status = (byte)(BUSMASTER_STATUS_MASK_INTERRUPT | BUSMASTER_STATUS_MASK_ERROR);
statusPort.Write8(status);
return;
} // BmPrepareController
private uint FillPrdTable(IdeRequest !ideRequest)
{
// given a memory address and a length generate
// a Physical Region Descriptor Table (PDRT) to be used
// in a IDE busmaster DMA transfer
//a PRDT table is an array of PRD entries, each 8 bytes in
//length. There is no count associated with this structure
// Bit 7 of the last byte of the last entry signifies the
//end of the table
// PRD (Physical Region Descriptor)
// the first 4 bytes of a PRD specify the memory address
// Bytes 5 and 6 (16 bits) specify the length.
// At most a PRD can specify a transfer of 64KB.
// The memory specified by a PRD cannot cross a 64KB boundary
// Any transfer that would cross such a boundary needs to be
// split into to separate PRDs
uint addr = (uint)((UIntPtr)ideRequest.BufferAddress + ideRequest.BufferOffset);
uint len = (uint)ideRequest.Length;
// Write a bad entry at the end
WritePrdEntry(PRD_MAX_ENTRIES - 1, 0, 0xbad1, true);
uint baseAddr = addr;
uint bytesToMap = len;
int i = 0;
while (0 != bytesToMap)
{
uint did = WritePrdChunk(i, baseAddr, bytesToMap);
baseAddr += did;
bytesToMap -= did;
i++;
}
// DEBUG CHECK
uint computedLen = 0;
bool eotFound = false;
for (i = 0; i < PRD_MAX_ENTRIES; i++)
{
uint dummy;
uint length;
bool eot;
ReadPrdEntry(i, out dummy, out length, out eot);
computedLen = computedLen + length;
if (eot)
{
eotFound = true;
break;
}
}
if (computedLen != len || !eotFound)
{
throw new ApplicationException("PRD length mismatch");
}
DumpPrd();
return((uint)prdRegion.PhysicalAddress.Value);
}
