Motorola MCP750 Specifications download pdf (Page 203)

Supporting Direct Memory Access (DMA)

12-5

else {

* we must add another chain pair

* return an error if there are too many discontiguous

* memory areas to fit in an HSA data chain.

if (chn >= HSHD_MAXCHAIN)

return (IMERR_XFER_TOO_LONG);

* construct a new chain pair here

* always set the LWC_DATA_CHAIN flag indicating

* that there are more pairs in the list.

mcb->hdw.chain[chn].ta = pa;

mcb->hdw.chain[chn].tc = bc | LWC_DATA_CHAIN;

* point to the next chain pair

* and remember the last physical address/bc from

* this pair.

chn++;

prevpa = pa;

prevbc = bc;

}

* increment the virtual buffer pointer and decrement

* the total length indicator

va += bc;

len -= bc;

} while (len > 0);

* on the way out, turn off the LWC_DATA_CHAIN

* bit on the last pair in the list.

* we are guaranteed that there will ALWAYS be

* at least 1 chain on the list (chn >= 1)

mcb->hdw.chain[chn-1].tc &= ~LWC_DATA_CHAIN;

* return success

return (0);

}

24-Bit DMA Devices 12

If the device uses a 32-bit DMA controller, it will be able to address any area of physical

memory on the Series 6000 platform. However, if the device provides only a 24-bit DMA

controller, the user or kernel area involved in the DMA transfer will not be accessible if

the area’s physical memory address is greater than 16 MB. A statically allocated kernel

buffer may be the best solution in this case.

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Motorola MCP750 Specifications Page 203