DAG Operations
4-12
ADSP-2126x SHARC Processor Hardware Reference
The following example instruction accepts up to 6-bit modifiers:
F6 = F1 + F2,PM(I8,0x0B) = ASTAT; /* PM address = I8,
I8 = I8 + 0x0B */
Note that pre-modify addressing operations must not change the
memory space of the address.
Data Addressing Stalls
As explained in the previous sections, the instruction sequence stalls for
one cycle if a read-after-write hazard is detected on a DAG register. For
example, the following sequence automatically generates a one cycle stall.
I0 = R0;
DM(I0,M0) = R1;
DAG conditional addressing can generate stalls if a post-modify instruc-
tion is aborted.
R2 = R3 – R4; /* Compute setting flags */
IF EQ DM(I1,M1) = R1; /* Flag is used immediately */
DM(I1,M2) = R2; /* Updated I1 is used immediately */
Note that even if the second instruction finds its condition true, a stall is
still inserted. Furthermore, if the second instruction is annulled because
the condition was false, then a stall is inserted in the address computation
(decode) stage of the third instruction. Note that a stall is generated only
if the above sequence is executed back-to-back.
Addressing Circular Buffers
The DAGs support addressing circular buffers. This is defined as address-
ing a range of addresses which contain data that the DAG steps through
repeatedly, “wrapping around” to repeat stepping through the range of
addresses in a circular pattern. To address a circular buffer, the DAG steps
the index pointer (
I
register) through the buffer, post-modifying and
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 ...