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Difference in the current consumption for different register place for few instructions

HimanshuDoshi19

Hello to all,

While working on different assembly instructions, I have come across a very different problem of the register's place. For example: 

SBC r11,r7,r11 : 3.0217mAmps

but 

SBC r11,r7,r7 : 2.7477mAmps

Similarly, for ORN and MVN also.

For all these (SBC, ORN, MVN) instructions.If

SBC Rd,Rn,Rd

or

ORN Rd, Rn, Rd

or

MVN Rd, Rd,

then the current consumption is comparatively high. This was seen only for these three instructions. Does anyone know about such behavior, present for these instructions?

I am working on ARM Cortex-M4.

Thanking you,

Regards,

Himanshu

Parents
  • 0 Arm Employee Badge in reply to HimanshuDoshi19

    Potentially that is down to the netlist level. Since the processor is delivered in Verilog RTL source, and chip vendors do the synthesis of RTL source to netlist, the use of adders and subtraction blocks and potentially part of the data paths could be very different in different implementations.

    Another potential factor is the instruction code being used. Is it both 16-bit in the comparison? or is one version using a 16-bit instruction and the other used a 32-bit instruction? When 32-bit instruction is used, more power could be used due to higher memory bandwidth for the program flash.

    regards,

    Joseph

Reply
  • 0 Arm Employee Badge in reply to HimanshuDoshi19

    Potentially that is down to the netlist level. Since the processor is delivered in Verilog RTL source, and chip vendors do the synthesis of RTL source to netlist, the use of adders and subtraction blocks and potentially part of the data paths could be very different in different implementations.

    Another potential factor is the instruction code being used. Is it both 16-bit in the comparison? or is one version using a 16-bit instruction and the other used a 32-bit instruction? When 32-bit instruction is used, more power could be used due to higher memory bandwidth for the program flash.

    regards,

    Joseph

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