Intel 81342 Developer's Manual page 684

8 . 3 . 3 . 1 E C C G e n e r a t i o n
F o r w r i t e o p e r a t i o n s , t h e S M C U g e n e r a t e s t h e e r r o r c o r r e c t i o n c o d e w h i c h i s w r i t t e n
a l o n g w i t h t h e d a t a . T h i s s e c t i o n d e s c r i b e s t h e o p e r a t i o n o f t h e S R A M C o n t r o l B l o c k f o r
E C C g e n e r a t i o n o n 3 2 - b i t d a t a o f t h e 2 5 6 - b i t w i d e m e m o r y . T h e S M C U w i l l g e n e r a t e 7 -
b i t w i d e E C C o n e v e r y 3 2 - b i t d a t a . T h e a l g o r i t h m f o r a w r i t e t r a n s a c t i o n i s :
if data to write is 32-bit wide
Generate the ECC_with the G-matrix
Write the new data and ECC
else {Partial Write}
Read entire 32-bit data word from memory
Merge the new data portion with the data from memory
Generate the new ECC with the G-matrix
Write new data and ECC
F i g u r e 1 0 1
t r a n s a c t i o n .
F i g u r e 1 0 1 . E C C W r i t e F l o w
M C U
T h e G - M a t r i x i n
m a t r i x a n d t h e o u t p u t i s t h e E C C c o d e . E a c h r o w o f t h e G - M a t r i x i n d i c a t e s w h i c h d a t a
b i t s ' c o d e s o f
X O R e d t o g e t h e r t o f o r m t h e E C C c o d e . T h e r e s u l t i n g E C C b i t s a r e d r i v e n o n
S C B 0 [ 6 : 0 ]
®
I n t e l 8 1 3 4 1 a n d 8 1 3 4 2 I / O P r o c e s s o r s
D e v e l o p e r ' s M a n u a l
6 8 4
s h o w s h o w t h e d a t a l o g i c a l l y f l o w s t h r o u g h t h e E C C h a r d w a r e f o r a w r i t e
S R A M M e m o r y A r r a y
M e m o r y
E C C
D [ 2 5 5 : 2 2 4 ]
C a c u l a t e
E C C
F i g u r e 1 0 1 g e n e r a t e s t h e E C C . T h e d a t a t o b e w r i t t e n i s i n p u t t o t h e
D Q [ 3 1 : 0 ] D Q [ 6 3 : 3 2 ]
,
S C B 1 [ 6 : 0 ] S C B 2 [ 6 : 0 ]
, ,
®
I n t e l 8 1 3 4 1 a n d 8 1 3 4 2 — S R A M M e m o r y C o n t r o l l e r
2 5 6 - b i t
D a t a P a t h
D Q [ 9 5 : 6 4 ] D Q [ 2 5 5 : 2 2 4 ]
, , o r
a n d S C B 7 [ 6 : 0 ] r e s p e c t i v e l y .
,
E C C M e m o r y D [ 3 1 : 0 ]
C a c u l a t e
E C C
B 6 3 5 8 - 0 1
n e e d s t o b e
D e c e m b e r 2 0 0 7
O r d e r N u m b e r : 3 1 5 0 3 7 - 0 0 2 U S