SH3-DSP General Registers
The SH-3 DSP series microprocessor family has 16 general registers, numbered R0-R15. Each register is 32 bits. When the DSP extended features of the SH3-DSP are enabled, DSP instructions use X and Y data memory and L bus data memory addressing for eight of the 16 general-purpose registers.
DSP-type instructions can access X and Y data memory simultaneously. To specify addresses for X and Y data memory, two address pointer sets are provided. The following list shows address pointer sets for DSP-type instructions:
- R8 [Ix], R4, R5 [Ax] for X memory access
- R9 [Iy], R6, R7 [Ay] for Y memory access
The following table shows memory and access conventions.
| Access Type | Address Register | Index Register |
|---|---|---|
| X memory | R4 and R5 X address register, Ax |
R8 X index register, Ix. |
| Y memory | R6 and R7 Y address register, Ay |
R9 Y index register, Iy. |
| Single data that uses L-bus |
R2, R3, R4, and R5 single data address register As |
R8 single data index register. |
In addition, when you enable the DSP extension, the SH3-DSP uses register R2–R9 for DSP data address calculation.
The following table shows the DSP Mode Enabled general register assignments for X and Y data transfer operations.
| Registers | Description |
|---|---|
| R4, R5 [Ax] | Address register set for X data memory. |
| R8 [x] | Index register for address register set Ax. |
| R6, R7 [Ay] | Address register set for Y data memory. |
| R9 [Iy] | Index register for address register set Ay. |
The following table shows the DSP Mode Enabled general register assignments for single data transfer operations.
| Registers | Description |
|---|---|
| R2–R5 [As] | Address register set for memory. |
| R8 [Is] | Index register for address register set As. |
The assembler uses the symbols R2 through R9, although users can use other register names or aliases that indicate the purpose of the register in the DSP instruction. The following code shows how to use Ix as an alias for R8.
Ix: .REG (R8)
The following table shows other aliases.
| Alias | Register | Comment |
|---|---|---|
| Ax0 | R4 | None. |
| Ax1 | R5 | None. |
| Ix | R8 | None. |
| Ay0 | R6 | None. |
| Ay1 | R7 | None. |
| Iy | R9 | None. |
| As0 | R4 | This is optional, if another alias is required for single data transfer. |
| As1 | R5 | This is optional, if another alias is required for single data transfer. |
| As2 | R2 | None. |
| As3 | R3 | None. |
| Is | R8 | This is optional, if another alias is required for single data transfer. |
See Also
SH3-DSP Registers | SH3-DSP Status Registers | SH3-DSP Control Registers | RS, RE, and ME Control Registers | SH3-DSP System Registers | DSP Unit Registers
Last updated on Thursday, April 08, 2004
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