Unicore

For the grid computing technology, see UNICORE.
Unicore
DesignerMicroprocessor Research and Development Center
Bits32-bit
Introduced1999
DesignRISC
EncodingFixed
BranchingCondition code
EndiannessLittle
Page size4 KiB
Registers
General-purpose31
Floating point32

Unicore is a computer instruction set architecture designed by the Microprocessor Research and Development Center (MPRC) of Peking University in the PRC. The computer built on this architecture is called the Unity-863.[1] The CPU is integrated into a fully functional SoC to make a PC-like system.[2]

The processor is very similar to the ARM architecture, but uses a different instruction set.[3][better source needed]

It is supported by the Linux kernel as of version 2.6.39.[4] Support will be removed in Linux 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]

Instruction set

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.

Unicore32 instruction set overview[8]
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 = Rn op Rm shift #shift
0 0 0 opcode S Rn Rd Rs 0 Sh 1 Rm ALU operation, Rd = Rn op Rm shift Rs
0 0 1 opcode S Rn Rd shift imm9 ALU operation, Rd = Rn op #imm9 ROTL #shift
0 1 0 P U B W L Rn Rd shift 0 Sh 0 Rm Load/store Rd to address Rn ± Rm shift #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.

References

  1. ^ "Introduction to MPRC". Microprocessor Research and Develop Center, Peking University.
  2. ^ Xu Cheng; Xiaoyin Wang; Junlin Lu; Jiangfang Yi; Dong Tong; Xuetao Guan; Feng Liu; Xianhua Liu; Chun Yang; Yi Feng (March 2010), "Research Progress of UniCore CPUs and PKUnity SoCs" (PDF), Journal of Computer Science and Technology (JCST), 25 (2): 200–213, doi:10.1007/s11390-010-9317-1, S2CID 7083916, retrieved 2012-07-11
  3. ^ Bergmann, Arnd (2012-07-09). "Re: [PATCH 00/36] AArch64 Linux kernel port". linux-kernel (Mailing list). Retrieved 2012-07-11. 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.
  4. ^ "Merge window closed - 2.6.39-rc1 out". Linus Torvalds.
  5. ^ "remove unicore32 support". Mike Rapoport.
  6. ^ Hsu-Hung Chiang; Huang-Jia Cheng; Yuan-Shin Hwan (2012-02-25), "Doubling the Number of Registers on ARM Processors" (PDF), 16th Workshop on Interaction between Compilers and Computer Architectures (INTERACT), pp. 1–8, doi:10.1109/INTERACT.2012.6339620, ISBN 978-1-4673-2613-1, S2CID 6832041
  7. ^ Unicore processor simulator source code. Instruction formats are in decode.c, disassembly in interpret.c, and emulation in instEx.c.
  8. ^ QEMU Unicore32 emulator source code


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