On 24-04-08 08:28, jeyram jadenthradevan wrote:
i am a beginner level in driver programming. please help to solve this
problem.
this is a part of the internal modem driver coding. this is for intel
chip set internal modem.
-------------------------------------------------------------------------------------------------------------------------------------------------------------
// ZT_MAX_CHUNKSIZE = 8
wc->writechunk = (int *)pci_alloc_consistent(pdev, ZT_MAX_CHUNKSIZE * 2
* 2 * 2 * 4, &wc->writedma);
if (!wc->writechunk) {
printk("wcfxo: Unable to allocate DMA-able memory\n");
if (wc->freeregion)
release_region(wc->ioaddr, 0xff);
return -ENOMEM;
}
wc->readchunk = wc->writechunk + ZT_MAX_CHUNKSIZE * 4; /* in
doublewords */
wc->readdma = wc->writedma + ZT_MAX_CHUNKSIZE * 16; /* in
bytes */
---------------------------------------------------------------------------------------------------------------------------------------------------------------
here they are creating 2 chunks for writing and reading.
but i couldn't understand this line.
wc->readdma = wc->writedma + ZT_MAX_CHUNKSIZE * 16;
why are they using ZT_MAX_CHUNKSIZE * 16 for allocating read chunk?
I gather "a chunk" is some entity consisting of 4 32-bit datums.
wc->writechunk is an int * I see from the cast and (I suppose) wc->writedma
is a char *. C pointer arrithmetic says p + i = (char *)p + i * sizeof(*p)
meaning both would end up at the same numeric value. I guess that was the
question?
Rene.
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