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authormokopatches <mokopatches@openmoko.org>2008-11-19 17:03:14 +0000
committerwarmcat <andy@warmcat.com>2008-11-19 17:03:14 +0000
commit2cae8d0e268fe753f3ae7af8c4989aa68bff40e9 (patch)
treea63c7924c34f526e5519830acfe6461dc20d5cc4 /REPORTING-BUGS
parent0792860061d14d0947973435ab644eb88dd0407a (diff)
s3c2410_udc-2440_dual_packet-workaround.patch
This is a patch that seems to make the USB hangs on the S3C2440 go away. At least a good amount of ping torture didn't make them come back so far. The issue is that, if there are several back-to-back packets, sometimes no interrupt is generated for one of them. This seems to be caused by the mysterious dual packet mode, which the USB hardware enters automatically if the endpoint size is half that of the FIFO. (On the 2440, this is the normal situation for bulk data endpoints.) There is also a timing factor in this. I think what happens is that the USB hardware automatically sends an acknowledgement if there is only one packet in the FIFO (the FIFO has space for two). If another packet arrives before the host has retrieved and acknowledged the previous one, no interrupt is generated for that second one. However, there may be an indication. There is one undocumented bit (none of the 244x manuals document it), OUT_CRS1_REG[1], that seems to be set suspiciously often when this condition occurs. There is also CLR_DATA_TOGGLE, OUT_CRS1_REG[7], which may have a function related to this. (The Samsung manual is rather terse on that, as usual.) This needs to be examined further. For now, the patch seems to do the trick. Note that this is not a clean solution by any means, because we might potentially get stuck in that interrupt for quite a while.
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