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Instruction Grouping
In the execution set described above, six SC140 instructions are grouped together. When executed, the
following occurs:
1. The contents of the D0 and D1 registers are multiplied fractionally. The result is added to the
content of the D7 data register. The final result is then stored in the D7 data register.
2. The contents of the D3 and D4 registers are multiplied fractionally. The result is added to
the content of the D6 data register. The final result is then stored in the D6 data register.
3. The contents of the D0 and D2 registers are multiplied fractionally. The result is added to
the content of the D5 data register. The final result is then rounded and stored in the D5 data
register.
4. The contents of the D3 and D4 registers are added together. The result is rounded and stored
in the D4 data register.
5. The contents of the 16-bit memory location pointed to by the R0 register is sign extended
and moved into the D2 register.
6. The content of the N3 register is added to the content of the R0 register. The result is stored
back in the R0 register.
7. The 32 least significant bits of the D0 register are moved to the R1 register.
5.2.1 Grouping Types
The SC140 grouping includes two types of encoding:
•
Serial (non-prefix) grouping, which encodes in the two most significant bits (MSB) of instructions.
•
Prefix grouping, which encodes a one-word or two-word prefix at the start of the execution set.
The Program Dispatch Unit (PDU) in the PSEQ determines which instructions in each clock cycle should
be issued to the execution units. It does this by decoding the grouping information.
In serial grouping, the value 00 in the two most significant bits (MS) of an instruction word indicates that
this word is to be grouped with the next instruction word. An instruction with a value other than 00 in its
two MS bits is considered the last instruction in the set, and marks the execution set boundary.
In prefix grouping, if a prefix exists at the beginning of an execution set, the PDU uses it to determine the
grouping information, including the number of instruction words grouped in the execution set.
Figure 5-2 illustrates the serial and prefix methods for the SC140 grouping mechanism:
Serial grouping
Prefix grouping
5-6
00
Prefix word(s)
011
Figure 5-2. Instruction Grouping Methods
Inst. #1
Inst. #2
00
Inst. #1
Inst. #2
SC140 DSP Core Reference Manual
Inst. #3
01
Inst. #3
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