Cirrus Logic EP93xx - Manual (Page 696)

22-8 DS785UM1
Copyright 2007 Cirrus Logic
AC’97 Controller
EP93xx User’s Guide
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Definition:
Receive Control Registers. The AC97RXCR registers are read/write registers
that are 32 bits. The data contained within the register controls the data slots
that are contained within the receive FIFO. The data contained within the
RSIZE bits controls the number of zeros that are to be appended to data to
make it 20 bits.
Should two channels be enabled for the same data slot, then data is taken
from, or given to, the lower channel number.
The data from the receive channel is stored in the lowest slot first. If for
example the receive FIFO is setup to store slots 3 and 4 then the first data
word out of the FIFO will be slot 3 followed by slot 4.
Bit Descriptions:
RSVD: Reserved. Unknown During Read.
TOC: Time out count value. The FIFOs have the capability of
generating a timeout interrupt when the receive FIFO is
not empty and no further data is received for a period of
time. This time period is specified by the value written
here. The value is the number of frames that must occur
without any data being received (a count of the SYNC
signal). A write of “0” to this value disables the counter,
and no timeout interrupt is generated. On reset the value
is “0”. The maximum count of 4096 will allow the timeout
period to be set to 85 msec.
FDIS: FIFO Disable
0 - The FIFO buffers are Enabled (FIFO mode).
1 - The FIFO is disabled (character mode). That is, the
FIFO becomes 1-byte-deep holding registers.
CM: Compact mode enable. If the RSIZE value is either “00” or
“11” (setting the data word size to 12- or 16-bits) then the
CM bit determines whether the two data words are
compacted into one 32-bit word, or each is sent in a
separate word. If the RSIZE value is either “01” or “10”
(setting the data word size to 18- or 20-bits) then the CM
bit has no effect. See
Table 22-3 .
0 - The data is justified into separate 32 bit words
1 - The two data words are compacted into one 32-bit
word for reading by the CPU.