Unicore

Last updated
Unicore
DesignerMicroprocessor Research and Development Center
Bits32-bit
Introduced1999
Design RISC
Encoding Fixed
Branching Condition code
Endianness Little
Page size4 KiB
Registers
General purpose 31
Floating point 32

Unicore is the name of 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
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26
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24
23
22
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18
17
16
15
14
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1
0
Description
000opcodeSRnRdshift0Sh0RmALU operation, Rd = Rn op Rm shift #shift
000opcodeSRnRdRs0Sh1RmALU operation, Rd = Rn op Rm shift Rs
001opcodeSRnRdshiftimm9ALU operation, Rd = Rn op #imm9 ROTL #shift
010PUBWLRnRdshift0Sh0RmLoad/store Rd to address Rn ± Rm shift #shift
011PUBWLRnRdoffset14Load/store Rd to address Rn ± offset14
100PUSWLRnBitmap high00HBitmap lowLoad/store multiple registers
101condLoffset24Branch (and link) if condition true
110Coprocessor (FPU) instructions
11111111Trap numberSoftware interrupt
000000ASRnRdRs1001RmMultiply, Rd = Rm * Rs (+ Rn)
0001000L1111111111000001001RmBranch and exchange (BX, BLX)
010PU0WLRnRd000001SH1RmLoad/store Rd to address Rn ± Rm (16-bit)
010PU1WLRnRdimm_hi1SH1imm_loLoad/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.

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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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