ADSP-2126x SHARC Processor Hardware Reference
5-19
Memory
using the Internal Memory Data Width (
IMDWx
) bits in the
SYSCTL
regis-
ter. If a block’s
IMDWx
bit is cleared (=0), normal word accesses to the block
access 32-bit data. If a block’s
IMDWx
bit is set (=1), normal word accesses
to the block access 48-bit data. If a program tries to write 40-bit data (for
example, a data register-to-memory transfer), the transfer truncates the
lower 8 bits from the register; only writing 32 most significant bits.
If a program tries to read 40-bit data (for example, a memory-to-data reg-
ister transfer), the transfer zero-fills the lower 8 bits of the register, only
reading the 32 most significant bits (MSBs).
The Program Memory Bus Exchange (
PX
) register is the only exception to
these transfer rules—all loads and or stores of the
PX
register are performed
as 48-bit accesses unless forced to a 64-bit access with the
LW
mnemonic. If
any 40-bit data must be stored in a memory block configured for 32-bit
words, the program uses the
PX
register to access the 40-bit data in 48-bit
words. Programs should take care not to corrupt any 32-bit data with this
type of access.
For more information, see “Restrictions on Mixing 32-Bit
Words and 48-Bit Words” on page 5-16.
The Long word (
LW
) mnemonic only effects normal word address
accesses and overrides all other factors (SIMD,
IMDWx
).
Secondary Processor Element (PEy)
When the
PEYEN
bit in the
MODE1
register is set (=1), the DSP is in Sin-
gle-Instruction, Multiple-Data (SIMD) mode. In SIMD mode, many data
access operations differ from the DSP’s default Single-Instruction, Sin-
gle-Data (SISD) mode. These differences relate to doubling the amount of
data transferred for each data access.
Accesses in SIMD mode transfer both an explicit (named) location and an
implicit (unnamed, complementary) location. The explicit transfer is a
data transfer between the explicit register and the explicit address, and the
implicit transfer is between the implicit register and the implicit address.
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 ...