ADSP-2126x Memory Map
5-16
ADSP-2126x SHARC Processor Hardware Reference
Restrictions on Mixing 32-Bit Words and 48-Bit Words
There are some restrictions that stem from the memory column rotations
for three-column data (48- or 40-bit words) and they relate to the way
that three-column data can mix with four-column data (32-bit words) in
memory. These restrictions apply to mixing 48- and 32-bit words, because
the DSP uses a normal word address to access both of these types of data
even though 48-bit data maps onto three columns of memory and 32-bit
data maps onto two columns of memory.
When a system has a range of three-column (48-bit) words followed by a
range of two-column (32-bit) words, there is often a gap of empty 16-bit
locations between the two address ranges. The size of the address gap var-
ies with the ending address of the range of 48-bit words. Because the
addresses within the gap alias to both 48- and 32-bit words, a 48-bit write
into the gap corrupts 32-bit locations, and a 32-bit write into the gap cor-
rupts 48-bit locations. The locations within the gap are only accessible
with short word (16-bit) accesses.
Calculating the starting address for four column data that minimizes the
gap after three column data is useful for programs that are mixing three
and four column data. Given the last address of the three column (48-bit)
data, the starting address of the 32-bit range that most efficiently uses
memory can be determined by the equation shown in
.
Listing 5-2. Starting Address
m = B + 2 [(n MOD K) – TRUNC (n MOD K) / 4)]
where:
•
K
is 21844 for RAM and 43690 for ROM
•
n
is the number of contiguous 48-bit words allocated in the inter-
nal memory block (n < 43,690 for ROM, n < 21844 for RAM)
Summary of Contents for ADSP-21261 SHARC
Page 30: ...Contents xxx ADSP 2126x SHARC Processor Hardware Reference ...
Page 40: ...Register Diagram Conventions xl ADSP 2126x SHARC Processor Hardware Reference ...
Page 58: ...Differences From Previous SHARCs 1 18 ADSP 2126x SHARC Processor Hardware Reference ...
Page 112: ...Secondary Processing Element PEy 2 54 ADSP 2126x SHARC Processor Hardware Reference ...
Page 178: ...Summary 3 66 ADSP 2126x SHARC Processor Hardware Reference ...
Page 204: ...DAG Instruction Summary 4 26 ADSP 2126x SHARC Processor Hardware Reference ...
Page 322: ...Setting Up DMA 7 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 436: ...SPORT Programming Examples 9 86 ADSP 2126x SHARC Processor Hardware Reference ...
Page 521: ...ADSP 2126x SHARC Processor Hardware Reference 11 31 Input Data Port rts IDP_ISR end ...
Page 522: ...Input Data Port Programming Example 11 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 590: ...Timer Programming Examples 14 20 ADSP 2126x SHARC Processor Hardware Reference ...
Page 796: ...I O Processor Registers A 174 ADSP 2126x SHARC Processor Hardware Reference ...
Page 800: ...B 4 ADSP 2126x SHARC Processor Core Manual ...
Page 846: ...Index I 36 ADSP 2126x SHARC Processor Hardware Reference ...