Motorola MVME2300 Series - Manual (Page 167)

Functional Description
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Functional Description
The following sections describe the logical function of the Falcon ASIC.
The Falcon is designed to be used as a set of two chips. A pair of Falcons
works with x1 or wider DRAM memory devices to form a memory system
for the PowerPC 60x bus. A pair of Falcons that is connected to implement
a memory control function is referred to in this document as a “Falcon
pair”.
Bit Ordering Convention
All Falcon bused signals are named using big-endian bit ordering (bit 0 is
the most significant bit).
Performance
The following sections describe the Falcon pair’s data transfer
characteristics in various configurations.
Four-beat Reads/Writes
The Falcon pair is specifically designed to provide maximum performance
for cache line (four-beat) cycles to and from the PowerPC 60x bus at
66MHz. This is done by providing a two-way interleave between the 64-
bit PowerPC 60x data bus and the 128-bit (144 with check-bits) DRAM
bus. When a PowerPC 60x bus master begins a quad-aligned, four-beat
read to DRAM, the Falcon pair accesses the full 144-bit width of DRAM
at once so that when the DRAM access time is reached, not only is the first
64-bit double-word of data ready to be transferred to the PowerPC 60x bus
master, but so is the next. While the Falcon pair is presenting the first two
double-words to the PowerPC 60x bus, it cycles CAS without cycling RAS
to obtain the next two double-words. The Falcon pair transfers the next two
double-words to the PowerPC 60x bus after 0 or more idle clocks.
The Falcon pair also profits from the fact that PowerPC 60x processors can
do address pipelining. Many times while a data cycle is finishing, the
PowerPC 60x processor begins a new address cycle. The Falcon pair can
begin the next DRAM access earlier when this happens, thus shortening