Chapter 14 AC-link Controller
14-7
14.3.4 AC-link Start Up
Figure 14.3.5 shows the conceptual sequence of AC-link start-up.
The ACLC Control Enable Register’s Enable AC-link bit is used to deassert/assert the ACRESET*
signal to the link side (including AC-link). This bit defaults to ‘0’, so the CPU asserts the ACRESET*
signal when it boots up.
The AC’97 specification requires that the reset assertion period is 1
µ
s or longer. The software is
responsible for controlling the length of this period.
The AC’97 specification also requires that the primary CODEC stops the AC-link clock (BITCLK)
signal during the period from ACRESET* signal assertion to 162.8ns after ACRESET* signal
deassertion. ACLC assumes the primary CODEC meet this requirement.
Deasserting the link-side reset makes the primary CODEC start driving the BITCLK signal. When
the BITCLK signal is provided, ACLC starts the SYNC signal output, which indicates the start of the
AC-link frame, and starts the frame-length counting.
When a CODEC becomes ready to receive access to its own register, the CODEC sets the “CODEC
Ready” bit of the Tag slot. When ACLC detects that this bit has been set, the ACLC Interrupt Status
Register (ACINTSTS)’s CODEC[1:0] Ready (CODEC[1:0]RDY) bit is set. The system software is
able to recognize the readiness of the CODEC(s) by detecting this event by way of either polling or
interrupt.
In case of 5.1 channel audio connection example (Figure 14.3.2), because the secondary CODEC is
connected to the
SDIN1
signal of ACLC, the software must watch ACINTSTS.CODEC1RDY bit to
determine the CODEC’s readiness for the register access.
Figure 14.3.5 Cold Reset and CODEC Ready Recognition
SDIN
ACRESET
*
BITCLK
SYNC
ENLINK
CODECRDY
ACLC internal clock becomes active
Software sets ENLINK bit
CODEC becomes ready to accept register access
Boot up
Note: The number of BITCLK cycles relative to other signals is not to scale.
Содержание TMPR4925
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