本帖最后由 zyzyzy407 于 2011-12-11 17:16 编辑
// The following section of code is used to relocate the descriptor table.
// The frameworks uses SUDPTRH and SUDPTRL to automate the SETUP requests
// for descriptors. These registers only work with memory locations
// in the EZ-USB internal RAM. Therefore, if the descriptors are located
// in external RAM, they must be copied to in internal RAM.
// The descriptor table is relocated by the frameworks ONLY if it is found
// to be located in external memory.
pDeviceDscr = (WORD)&DeviceDscr;
pDeviceQualDscr = (WORD)&DeviceQualDscr;
pHighSpeedConfigDscr = (WORD)&HighSpeedConfigDscr;
pFullSpeedConfigDscr = (WORD)&FullSpeedConfigDscr;
pStringDscr = (WORD)&StringDscr;
// Is the descriptor table in external RAM (> 16Kbytes)? If yes,
// then relocate.
// Note that this code only checks if the descriptors START in
// external RAM. It will not work if the descriptor table spans
// internal and external RAM.
if ((WORD)&DeviceDscr & 0xC000)
{
// first, relocate the descriptors
IntDescrAddr = INTERNAL_DSCR_ADDR;
ExtDescrAddr = (WORD)&DeviceDscr;
DevDescrLen = (WORD)&UserDscr - (WORD)&DeviceDscr + 2;
for (i = 0; i < DevDescrLen; i++)
*((BYTE xdata *)IntDescrAddr+i) = *((BYTE xdata *)ExtDescrAddr+i);
// update all of the descriptor pointers
pDeviceDscr = IntDescrAddr;
offset = (WORD)&DeviceDscr - INTERNAL_DSCR_ADDR;
pDeviceQualDscr -= offset;
pConfigDscr -= offset;
pOtherConfigDscr -= offset;
pHighSpeedConfigDscr -= offset;
pFullSpeedConfigDscr -= offset;
pStringDscr -= offset;
}
这段程序没怎么看懂 就只知道大概是从片外移描述符到片内吧 麻烦具体讲讲 |
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