Table of Contents
Advertisement
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 1µs 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.
ACRESET*
BITCLK
SYNC
SDIN
ENLINK
CODECRDY
Boot up
Software sets ENLINK bit
ACLC internal clock becomes active
Figure 14.3.5 Cold Reset and CODEC Ready Recognition
Chapter 14 AC-link Controller
CODEC becomes ready to accept register access
Note: The number of BITCLK cycles relative to other signals is not to scale.
14-7
Advertisement
Table of Contents
