Texas Instruments TMS320C3x - Manual (Page 175)

Circular Addressing
6-22
Figure 6–6. Logical and Physical Representation of Circular Buffer after Writing Eight Values
Start End
a) Logical representation
value6
value7
value2
value6
value2
value7
b) Physical representation
value5
value3
value4
value3
value4
value5
Start
End
To implement a circular buffer in the ’C3x, the following criteria must be satis-
fied (more than one circular buffer can be implemented on the ’C3x as long as
the size of the buffers are identical):
- Specify the size of the circular buffer (R) by storing the length of the buffer
in the block-size register (BK). The size of the buffer must be less than or
equal to 64K (16 bits).
- Align the start of the buffer to a K-bit boundary (that is, the K LSBs of the
starting address of the circular buffer must be 0) by satisfying the following
formula:
2 K > R
where:
R = length of circular buffer
K = number of 0s in the LSBs of the circular buffer starting address
Example 6–23. Examples of Formula 2 K > R
Length of Buffer BK Register Value Starting Address of Buffer
31 31 XXXXXXXXXXXXXXXXXXX00000
2
32 32 XXXXXXXXXXXXXXXXXX000000
2
1024 1024 XXXXXXXXXXXXX00000000000
2