
June 1997
171
ADVANCE DATA BOOK v2.0
FLOATING-POINT INSTRUCTION SET
CL-PS7500FE
System-on-a-Chip for Internet Appliance
The length field is encoded into bits 22 and 15 as shown in
Table 19-1
.
The offset in bits [7:0] is specified in words and is added to (U/D = 1) or subtracted from (U/D = 0) a base
register (Rn), either before (P = 1) or after (P = 0) the base is used as the transfer address. The modified
base value may be written back into the base register (Wb = 1) or the old value of the base may be pre-
served (Wb = 0).
NOTE:
Post-indexed addressing modes require explicit setting of the Wb bit, unlike LDR and STR that always write-
back when post-indexed. The value of the base register, modified by the offset in a pre-indexed instruction,
is used as the address for the transfer of the first word. The second word (if more than one is transferred)
goes to or comes from an address one word (4 bytes) higher than the first transfer, and the address incre-
ments by one word for each subsequent transfer.
19.1.2
Assembler Syntax
<LDF|STF>{cond}<S|D|E|P> Fd,[Rn]
[Rn, <#expression>]{!}
[Rn],<#expression>
Pre-indexed Addressing Specification
[Rn]
offset of zero
[Rn, #<expression>]{!}
offset of <expression> bytes
{!}
Write back the base register (set the Wb bit) if ! is
present.
NOTE:
If Rn is R15, writeback should not be specified.
Post-indexed Addressing Specification
[Rn],#<expression>
offset of <expression> bytes
NOTE:
The assembler automatically sets the Wb bit in this case. R15 should not be used as the base register where
post-indexed addressing is used. The
<expression>
must be divisible by 4 and be in the range
1020 to
1020.
a
LDFP and STFP are deprecated instructions and are intended for backwards compatibility only.
These functions should be implemented by appropriate calls to a C library.
Table 19-1. Length Field
Precision
Bit
22
Bit
15
FPSR.EP
Data Format
Size
Note
Single
S
0
0
x
1 memory word
Double
D
0
1
x
2 memory word
Extended
E
1
0
x
3 memory word
Packed decimal
P
1
1
0
3 memory word
a
Expanded packed decimal
EP
1
1
1
4 memory word
a