diff options
Diffstat (limited to 'sys/dev/usb/uhcivar.h')
| -rw-r--r-- | sys/dev/usb/uhcivar.h | 22 |
1 files changed, 13 insertions, 9 deletions
diff --git a/sys/dev/usb/uhcivar.h b/sys/dev/usb/uhcivar.h index 8169526..9af98b7 100644 --- a/sys/dev/usb/uhcivar.h +++ b/sys/dev/usb/uhcivar.h @@ -39,17 +39,21 @@ */ /* + * The framelist: + * * To avoid having 1024 TDs for each isochronous transfer we introduce - * a virtual frame list. Every UHCI_VFRAMELIST_COUNT entries in the real - * frame list points to a non-active TD. These, in turn, which form the - * starts of the virtual frame list. This also has the advantage that it - * simplifies linking in/out TD/QH in the schedule. - * Furthermore, initially each of the inactive TDs point to an inactive - * QH that forms the start of the interrupt traffic for that slot. - * Each of these QHs point to the same QH that is the start of control - * traffic. + * a virtual frame list. Every UHCI_VFRAMELIST_COUNT'th entry in the real + * frame list points to a non-active TD. This TD is + * UHCI_FRAMELIST_COUNT/UHCI_VFRAMELIST_COUNT times the start of the + * virtual frame list for a queue of isochroneous transfers. + * + * The last isochroneous transfer in the list points to a QH for the + * interrupt transfer in that timeslot. The QHs for interrupt transfers + * all point to the single QH for control transfers, which in turn + * points at the QH for control transfers. * - * UHCI_VFRAMELIST_COUNT should be a power of 2 and <= UHCI_FRAMELIST_COUNT. + * UHCI_VFRAMELIST_COUNT should be a power of 2 and UHCI_FRAMELIST_COUNT + * should be a multiple of UHCI_VFRAMELIST_COUNT. */ #define UHCI_VFRAMELIST_COUNT 128 |
