| Designer | Microprocessor Research and Development Center |
|---|---|
| Bits | 32-bit |
| Introduced | 1999 |
| Design | RISC |
| Encoding | Fixed |
| Branching | Condition code |
| Endianness | Little |
| Page size | 4 KiB |
| Registers | |
| General-purpose | 31 |
| Floating point | 32 |
Unicore is a computerinstruction set architecture designed by the Microprocessor Research and Development Center (MPRC) ofPeking University in thePRC. The computer built on this architecture is called theUnity-863.[1]The CPU is integrated into a fully functional SoC to make a PC-like system.[2]
The processor is very similar to theARM architecture, but uses a different instruction set.[3][better source needed]
It is supported by theLinux kernel as of version 2.6.39.[4]Support will be removed inLinux kernel version 5.9 as nobody seems to maintain it and the code is falling behind the rest of the kernel code and compiler requirements.[5]
The instructions are almost identical to the standard ARM formats, except that conditional execution has been removed, and the bits reassigned to expand all the register specifiers to 5 bits.[6][7] Likewise, the immediate format is 9 bits rotated by a 5-bit amount (rather than 8 bit rotated by 4), the load/store offset sizes are 14 bits for byte/word and 10 bits for signed byte or half-word. Conditional moves are provided by encoding the condition in the (unused by ARM) second source register field Rn for MOV and MVN instructions.
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | Description |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 0 | 0 | opcode | S | Rn | Rd | shift | 0 | Sh | 0 | Rm | ALU operation, Rd = Rnop Rmshift #shift | ||||||||||||||||||||
| 0 | 0 | 0 | opcode | S | Rn | Rd | Rs | 0 | Sh | 1 | Rm | ALU operation, Rd = Rnop Rmshift Rs | ||||||||||||||||||||
| 0 | 0 | 1 | opcode | S | Rn | Rd | shift | imm9 | ALU operation, Rd = Rnop #imm9 ROTL #shift | |||||||||||||||||||||||
| 0 | 1 | 0 | P | U | B | W | L | Rn | Rd | shift | 0 | Sh | 0 | Rm | Load/store Rd to address Rn ± Rmshift #shift | |||||||||||||||||
| 0 | 1 | 1 | P | U | B | W | L | Rn | Rd | offset14 | Load/store Rd to address Rn ± offset14 | |||||||||||||||||||||
| 1 | 0 | 0 | P | U | S | W | L | Rn | Bitmap high | 0 | 0 | H | Bitmap low | Load/store multiple registers | ||||||||||||||||||
| 1 | 0 | 1 | cond | L | offset24 | Branch (and link) if condition true | ||||||||||||||||||||||||||
| 1 | 1 | 0 | Coprocessor (FPU) instructions | |||||||||||||||||||||||||||||
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | Trap number | Software interrupt | |||||||||||||||||||||||
| 0 | 0 | 0 | 0 | 0 | 0 | A | S | Rn | Rd | Rs | 1 | 0 | 0 | 1 | Rm | Multiply, Rd = Rm * Rs (+ Rn) | ||||||||||||||||
| 0 | 0 | 0 | 1 | 0 | 0 | 0 | L | 11111 | 11111 | 00000 | 1 | 0 | 0 | 1 | Rm | Branch and exchange (BX, BLX) | ||||||||||||||||
| 0 | 1 | 0 | P | U | 0 | W | L | Rn | Rd | 00000 | 1 | S | H | 1 | Rm | Load/store Rd to address Rn ± Rm (16-bit) | ||||||||||||||||
| 0 | 1 | 0 | P | U | 1 | W | L | Rn | Rd | imm_hi | 1 | S | H | 1 | imm_lo | Load/store Rd to address Rn ± #imm10 (16-bit) | ||||||||||||||||
The meaning of various flag bits (such as S=1 enables setting the condition codes) is identical to the ARM instruction set. The load/store multiple instruction can only access half of the register set, depending on the H bit. If H=0, the 16 bits indicate R0–R15; if H=1, R16–R31.
Another interesting example is unicore32, which actually shares more code with arch/arm than the proposed arch/aarch64 does. I think the unicore32 code base would benefit from being merged back into arch/arm as a third instruction set, but the additional maintenance cost for everyone working on ARM makes that unrealistic.
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