80KSBR200 Datasheet, PDF (29/172 Pages) Integrated Device Technology – sRIO SERIAL BUFFER FLOW-CONTROL DEVICE

IDT 80KSBR200
Notes
Advanced Datasheet*
lems with the waterlevel timer if packet counts are used. It is expected that all antennas will send data at very stable rates,
so the combination of two or more sending packets with different sizes will not interfere with the overall timing if the total
quantity is adjusted to accommodate the combined larger number.
Packet Ready
This mode may be used to indicate that at least one packet is available in the queue for reading. The flag will toggle,
indicating that one or more packets is in the queue. The following is the setup.
◆ _{Queue is programmed to be a slave}
◆ _{Waterlevel is programmed to use packets}
◆ _{Watermark is set to desired level.}
◆ _{The flag masks should be programmed to send the desired interrupt or doorbell to the correct recipients}
◆ _{The flag will toggle whenever the packet count in the queue goes from zero to one. The flag will remain active}
as long as the packet count equals or exceeds one.
Space Available at the Inn
This is the reverse of the Packet Ready scenario. When feeding data into any of the ports, it may be necessary to know
that there is room to accept the packet or more data. There are a couple of ways to for the user to accomplish this:
◆ _{Use the same scenario as "Packet Ready" and but set the waterlevel to one full sized packet below the queue}
size. An interrupt pin could be used as a "space available" pin.
◆ _{There is a flag on the Space Available counter to indicate that there is space for one more full sized packet in}
the queue. This flag could be used as an interrupt to indicate when the space has fallen below the designated
quantity (one packet plus some extra to accommodate latency in shutdown). The space available counter is in
the waterlevel register.
◆ _{Use the PAF and PAE flags to generate an interrupt or doorbell. This would give a more general indication of}
the space available, while preserving the watermark for other uses.
The Flag of Impending Doom
In this scenario, the watermark may be programmed more accurately than the partial flags and could be used as an
almost full flag or an almost empty flag. The flag could be used to indicate to the user that immediate action must be taken
to avoid overflow or underflow.
4.7 Missing Packet Detection and Packet Replacement
In the wireless basestation application that uses the PPS, a missing packet can cause havoc to the overall system. To
help overcome occasional missing packets, a missing packet detection and replacement can be performed.
There are four configuration registers that are programmed by the user. The registers contain Memory Start Address,
Current Memory Address, Memory Address Increment, and Memory Stop Address. It is expected in the PPS applica-
tion that all packets bound for a single DSP will be equal sized and have equal address increments, allowing the Memory
Address Increment to be used to detect incoming missing packets. When a packet comes into the PPS, the PPS may
segment the packet into 8 segments. The SerB will detect missing packets through the use of the address field in the
packet header.
In the PPS application, it is expected that the user will be performing memory writes through sequential addresses.
Missing packets may be detected by insuring that the first packet starts on the Memory Start Address and the address
associated with every subsequent address matches the previous packet address plus the Memory Address Increment. In
other words, the Current Memory Address plus the Memory Address Increment should be the new Current Memory
Address of the next incoming packet. If a packet is missed, the address should match the Current Memory Address plus
the Memory Address Increment added twice. Upon failing that, it is assumed that more than one packet was lost, or some
serious failure occurred and the flag is set in the flag register. Upon a serious failure, the Current Memory Address in the
incoming packet should be loaded into to the Current Memory Address register, and the SerB will attempt to compare the
new Current Memory Address plus Memory Address Increment with the subsequent packet address.
Missing packet detection requires the spacing of the addresses to hold at least two packets. It is not expected that
missing packet detection will function properly with only one packet available. If two or more packets are missing, the
missing packet detection may require the spacing of the minimum and maximum addresses to allow for storage of at least
three packets between the addresses.
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March 19, 2007
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