CY28342
Document #: 38-07349 Rev. *A
Page 11 of 22
System Self-recovery Clock Management
This feature is designed to allow the system designer to
change frequency while the system is running and reboot the
operation of the system in case of a hang up due to the
frequency change.
When the system sends an SMBus command requesting
a frequency change through byte 4 or through bytes 13 and
14, it must have previously sent a command selecting which
time-out stamp the Watchdog must perform to byte 12, or the
system self-recovery feature will not be applicable. Conse-
quently this device will change frequency, and then the
Watchdog timer starts timing. Meanwhile, the system BIOS is
running its operation with the new frequency. If this device
receives a new SMBus command to clear the bits originally
programmed in byte 12, bits(3:0) (reprogram to 0000) before
Watchdog times out, this device will keep operating in its
normal condition with the new selected frequency. If the
Watchdog times out the first time before the new SMBus repro-
grams byte 12, bits(3:0) to (0000), then this device will send
a low system reset pulse, on SRESET# (see byte 12, bit 7),
and changes the Watchdog alarm (byte 12, bit 4) status to “1”
then restarts the Watchdog timer. If the Watchdog times out
a second time, this device will send another low pulse on
SRESET#, will relatch original hardware strapping frequency
(or second-to-last software-selected frequency, see byte 12,
bit6) selection, set Watchdog alarm bit (byte 12, bit4) to “1,”
then start the Watchdog timer again. The above-described
sequence will keep repeating until the BIOS clears the SMBus
byte 12 bits(3:0). Once the BIOS sets byte 12 bits(3:0) = 0000,
the Watchdog timer is turned off and the Watchdog alarm bit
(byte 12, bit 4) is reset to “0.”
S y s t e m r u nn i n g w i t h
o r ig in a lly s e le c t e d
f r eq ue nc y v i a
h a rd w a re s t ra p p i n g .
R e c e i v e F r eq ue nc y
C h ang e R e qu es t v i a
SM Bu s By t e 4 o r V i a D i a l -
a - f r eq ue nc y ?
S t a r t i n te r n a l w a tc h d o g ti m e r .
W a t c h D o g t i m e ou t ?
T u r n o f f w a t c h do g
t i m e r .
K e e p n e w fr e q u e n c y s e tti n g . S e t W D a l a r m
bi t ( b y t e 1 2 , b i t 4 ) t o ’’0 ’
1 )
S e nd a n o t h e r 3m S l o w pu l s e on S R E S E T
2 )
R e la t c h o r ig in a l h a r d w a r e s t r a p p in g s e l e c t io n
fo r r e t u r n t o o r i g i n a l fr e q u e n c y s e tti n g s .
3 ) S e t W D A l a r m
b i t ( b y t e 1 2 , B i t 4 ) to " 1 "
4 ) S t a r t W D ti m e r
F r eq ue nc y w i l l c h a n g e bu t S y s t e m
S e l f
R e c o v e r y no t a p p l i c ab l e ( n o t i m e s t am p
s e l e c t e d an d by t e 12 , b i t ( 3: 0) i s s t i l l =
" 0 000 "
No
No
Ye s
No
No
Ye s
SM Bu s b y t e 1 2 t i m e
ou t s t am p d i s a bl ed ?
Is S M B u s B y te 9 , ti m e o u t
s t am p en abl e d - ( b y t e 12 , b i t
( 3 :0 )
0 0 0 0 ) ?
C h an ge t o a n e w
f r eq ue nc y
Ye s
1 ) Se n d S R ES ET
pu l s e
2) S e t W D bi t
( b y t e1 2, bi t 4 ) t o ’1 ’
3 ) S t a r t W D t i m e r
Ye s
W a tc h D o g ti m e o u t?
No
Ye s
S M B u s b y te 9 ti m e o u t
s t am p d i s a bl ed , B y t e
1 2 , bi t ( 3 : 0) = ( 0 00 0) ?
Ye s
No