
164
Agere Systems Inc.
Data Sheet
May 2001
and Packet Payload Engine
Ambassador T8110 PCI-Based H.100/H.110 Switch
14
Connection Control—Standard and Virtual Channel
(continued)
14.2.3.4.5 External Buffer Data Transfer
After the descriptor table fetch, the T8110 then does the following:
n
It either dumps its internal buffer of gathered TDM data to the external buffer space (
push
, a PCI memory write
burst of internal buffer size)
n
Or fetches data from the external buffer space into its internal buffer for outgoing TDM data (
pull
, a PCI memory
read burst of internal buffer size).
n
Or skips the external buffer data transfer (based on descriptor table status, such as a pointer stall, end-of-buffer
stall, buffer locked status, which indicate that the external buffer is not currently available to the T8110).
14.2.3.4.6 Descriptor Table Update
The T8110 then updates the descriptor table (second DWORD only), with values calculated based on the descrip-
tor table fetch results. The only allowable portions writable by T8110 include the GBS status, TF, and TOR. The
transfer is a PCI memory write of 1 DWORD.
14.2.3.5 T8110 Packet Switching, Circuit Operation
Each programmed T8110 virtual channel operates independently, and tracks both its current position in the T8110
internal buffer space and the buffer full (
push
) or empty (
pull
) status, in the scratchpad portion of the virtual chan-
nel memory (refer to Section 14.2.1.3). Upon determination of a full (or empty) internal buffer, that channel places
an entry into a notify queue and sets a bit in the notify pending memory. Entries in the notify queue get translated
into the T8110-initiated external buffer transfer protocol (refer to Section 14.2.3.4.4). Upon completion of that trans-
fer protocol, the notify pending memory bit for that channel is reset.