Count
to 32
External
AHCLKR
pin input
Sync to
system
clock
8−bit
counter
Clear
Count
Prescale
/1 to
/256
McASP
clock
(A)
system
4
RCLKCHK[3−0]
RPS
Load
RCLKCHK[31−24]
RCNT
8
RMIN
RCLKCHK[15−8]
8
RCNT<RMIN?
8
RCLKCHK[23−16]
RMAX
8
Counter>RMAX?
8
OR
True
True
RCKFAIL
RSTAT.2
Set
Interrupt
mute
Functional Description
22.3.10.4.6.3
Receive Clock Failure Check and Recovery
The receive clock failure check circuit (
) works off both the internal McASP system clock and
the external high-frequency serial clock (AHCLKR). It continually counts the number of system clocks for
every 32 high rate serial clock (AHCLKR) periods, and stores the count in RCNT of the receive clock
check control register (RCLKCHK) every 32 high rate serial clock cycles.
The logic compares the count against a user-defined minimum allowable boundary (RMIN) and
automatically flags an interrupt (RCKFAIL in RSTAT) when an out-of-range condition occurs. An out-of-
range minimum condition occurs when the count is smaller than RMIN. The logic continually compares the
current count (from the running system clock counter) against the maximum allowable boundary (RMAX).
This is in case the external clock completely stops, so that the counter value is not copied to RCNT. An
out-of-range maximum condition occurs when the count is greater than RMAX. Note that the RMIN and
RMAX fields are 8-bit unsigned values, and the comparison is performed using unsigned arithmetic.
An out-of-range count may indicate either that an unstable clock was detected or that the audio source
has changed and a new sample rate is being used.
In order for the receive clock failure check circuit to operate correctly, the high-frequency serial clock
divider must be taken out of reset regardless if AHCLKR is internally generated or externally sourced.
Figure 22-32. Receive Clock Failure Detection Circuit Block Diagram
A
Refer to device data manual for the McASP system clock source. This is not the same as AUXCLK.
3814
Multichannel Audio Serial Port (McASP)
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated