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FS#8830 - Sansa: DMA support for sd-card data access (experimentary)
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DetailsFirst approach, to add dma read/write disk access to the sansa.
There are some restrictions on the dma functionality with this patch: - only stabile at 80MHz => cpu boost control added to the driver - only on 16byte aligned data ptr => all data are copied to/from aligned memory - no interrupt support => using polling method At 30MHz the driver is much more stable with the following PLL settings: PLL_CONTROL = 0x8a221e0c; /* 30 MHz = (48MHz/12*30) / 4 */ CLOCK_SOURCE = 0x40007777; /* source #1, #2, #3, #4: PLL (#4 active) */ Reading seems to be in general more reliable than writing of the cards. The data throughput is a little worse than in the current implementation. This is partly due to the data copying. The sporadical '2bytes inserted' problem with the USB file transfer is still there. Interestingly @30MHz with the above settings, there is another problem: sporadically '2bytes missing' and '2bytes inserted'. Perhaps the DMA transfer needs some more initialization for proper synchronization. 
sd_dma.diff
(6.9 KiB)
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This task depends upon
Is there a lot of cpu involved with the current implementation(SVN)?
How is your progress since this patch is 1 month old?
Without DMA:
Create: 27 files/s
Open: 54 files/s
Dirscan: 6269 fils/s
Delete: 56 files/s
Create Write Read (KB/sec)
512,A 276 266 925
512,U 272 268 916
4096,A 1462 1439 4499
4096,U 1478 1462 4494
1048576,A 3900 3881 9836
1048576,U 3915 4046 9138
With DMA:
Create: 25 files/s
Open: 55 files/s
Dirscan: 5784 files/s
Delete 51 files/s
Create Write Read (KB/sec)
512,A 252 252 830
512,U 265 269 803
4096,A 1324 1314 3742
4096,U 1374 1369 2664
1048576,A 4087 4079 7198
1048576,U 4031 4104 7013
This seems to show that working with DMA is slower than working without it. This is partly to be expected as the driver yields while waiting for the transfer to finish.