CCS/MSP430F6736A: [CCS] MPY command take too long cycle time for customer source code.

Ernest Cho

Part Number: MSP430F6736A

Tool/software: Code Composer Studio

Hello Champs,

One of my customer is asking me their MPY command in the ISR takes long time comparing IAR compiler.
So I tried to reproduce it, but I can't reproduced it. I asked them to support source code but they can't due to the security issue.

1. They just sent me the C++ code with disassembled code and map file. I am attaching it.
This source code is executed at DMA ISR and DMA is triggered when 3ch SD24 is converted.
Their source code is C++ based and file extension is .cpp.
Compiler option is set as use the MPY(F5). This means they did as below :
- MSP430 Compiler - Optimization - "--use_hw_mpy=F5"
- MSP430 Compiler - Advanced Options - Advanced Optimization - "--disable_interrupts_around_hw_mpy=On" <- they need because several interrupt use mpy
- MSP430 Linker - Advanced Options - Symbol Management - "--use_hw_mpy=F5"

Their result shows over 1000 cycles for excuting 3 C/C++ commands below. I don't remember it exactly, but it takes 32, 32, 1600 something accordingly.

*(int32_t *)(&MPYS32L) = adc_buf[BSP_METROLOGY_AFE_VOLTAGE_A_CHANNEL];
*(int32_t *)(&OP2L) = *(int32_t *)(&MPYS32L);
afe_data->V_RMS_Src += *(int64_t *)(&RES0);

With the same source code, but when they tried on IAR showed around 365 cycles in total of 3 commands.

2. I just tried to reproduced it using CCSv8 with simple periodic timer and inserted code inside the ISR.
But it just take 17(in case of local variable) or 36(in case of global variable) cycles.

Q) : How can they modify the source code for reducing cycles? Could you suggest some modification?
I agree they use pointer structure take some more assembly operation, but huge difference between CCS and IAR.

cf) : They have some issue using IAR, IAR can't use over 4KB RAM for F6736 which have 8KB RAM. So they got in trouble to use both CCS and IAR.

625           *(int32_t *)(&MPYS32L) = adc_buf[BSP_METROLOGY_AFE_VOLTAGE_A_CHANNEL];
01203e:   41A2 04D4           MOV.W   @SP,&MPY_32__Multiplier__32_Bit_Mode_MPYS32L
012042:   4192 0002 04D6      MOV.W   0x0002(SP),&MPY_32__Multiplier__32_Bit_Mode_MPYS32H
626           *(int32_t *)(&OP2L) = *(int32_t *)(&MPYS32L);
012048:   4292 04D4 04E0      MOV.W   &MPY_32__Multiplier__32_Bit_Mode_MPYS32L,&MPY_32__Multiplier__32_Bit_Mode_OP2L
01204e:   4292 04D6 04E2      MOV.W   &MPY_32__Multiplier__32_Bit_Mode_MPYS32H,&MPY_32__Multiplier__32_Bit_Mode_OP2H
627           afe_data->V_RMS_Src += *(int64_t *)(&RES0);
012054:   013F 002C           MOVA    0x002c(SP),R15
012058:   0F71 0044           MOVA    R15,0x0044(SP)
01205c:   00AF 001F           ADDA    #0x0001f,R15
012060:   0F71 0048           MOVA    R15,0x0048(SP)
012064:   4F58 0003           MOV.B   0x0003(R15),R8
012068:   4309                CLR.W   R9
01206a:   430A                CLR.W   R10
01206c:   430B                CLR.W   R11
01206e:   403C 0018           MOV.W   #0x0018,R12
012072:   13B1 DF8A           CALLA   #__mspabi_sllll
012076:   4C81 0034           MOV.W   R12,0x0034(SP)
01207a:   4D81 0036           MOV.W   R13,0x0036(SP)
01207e:   4E81 0038           MOV.W   R14,0x0038(SP)
012082:   4F81 003A           MOV.W   R15,0x003a(SP)
012086:   013F 0048           MOVA    0x0048(SP),R15
01208a:   4F58 0001           MOV.B   0x0001(R15),R8
01208e:   4309                CLR.W   R9
012090:   430A                CLR.W   R10
012092:   430B                CLR.W   R11
012094:   423C                MOV.W   #8,R12
012096:   13B1 DF8A           CALLA   #__mspabi_sllll
01209a:   013B 0048           MOVA    0x0048(SP),R11
01209e:   4B64                MOV.B   @R11,R4
0120a0:   4305                CLR.W   R5
0120a2:   4306                CLR.W   R6
0120a4:   4307                CLR.W   R7
0120a6:   DC04                BIS.W   R12,R4
0120a8:   DD05                BIS.W   R13,R5
0120aa:   DE06                BIS.W   R14,R6
0120ac:   DF07                BIS.W   R15,R7
0120ae:   0BCF                MOVA    R11,R15
0120b0:   4F5F 0002           MOV.B   0x0002(R15),R15
0120b4:   DF05                BIS.W   R15,R5
0120b6:   D306                BIS.W   #0,R6
0120b8:   D307                BIS.W   #0,R7
0120ba:   D304                BIS.W   #0,R4
0120bc:   D114 0034           BIS.W   0x0034(SP),R4
0120c0:   D115 0036           BIS.W   0x0036(SP),R5
0120c4:   D116 0038           BIS.W   0x0038(SP),R6
0120c8:   D117 003A           BIS.W   0x003a(SP),R7
0120cc:   0BCF                MOVA    R11,R15
0120ce:   4F5F 0004           MOV.B   0x0004(R15),R15
0120d2:   DF06                BIS.W   R15,R6
0120d4:   D305                BIS.W   #0,R5
0120d6:   D307                BIS.W   #0,R7
0120d8:   D304                BIS.W   #0,R4
0120da:   0BCF                MOVA    R11,R15
0120dc:   4F58 0005           MOV.B   0x0005(R15),R8
0120e0:   4309                CLR.W   R9
0120e2:   430A                CLR.W   R10
0120e4:   430B                CLR.W   R11
0120e6:   403C 0028           MOV.W   #0x0028,R12
0120ea:   13B1 DF8A           CALLA   #__mspabi_sllll
0120ee:   DC04                BIS.W   R12,R4
0120f0:   DD05                BIS.W   R13,R5
0120f2:   DE06                BIS.W   R14,R6
0120f4:   DF07                BIS.W   R15,R7
0120f6:   013F 0048           MOVA    0x0048(SP),R15
0120fa:   4F5F 0006           MOV.B   0x0006(R15),R15
0120fe:   DF07                BIS.W   R15,R7
012100:   D305                BIS.W   #0,R5
012102:   D306                BIS.W   #0,R6
012104:   D304                BIS.W   #0,R4
012106:   013F 0048           MOVA    0x0048(SP),R15
01210a:   4F58 0007           MOV.B   0x0007(R15),R8
01210e:   4309                CLR.W   R9
012110:   430A                CLR.W   R10
012112:   430B                CLR.W   R11
012114:   403C 0038           MOV.W   #0x0038,R12
012118:   13B1 DF8A           CALLA   #__mspabi_sllll
01211c:   DC04                BIS.W   R12,R4
01211e:   DD05                BIS.W   R13,R5
012120:   DE06                BIS.W   R14,R6
012122:   DF07                BIS.W   R15,R7
012124:   5214 04E4           ADD.W   &MPY_32__Multiplier__32_Bit_Mode_RES0,R4
012128:   6215 04E6           ADDC.W  &MPY_32__Multiplier__32_Bit_Mode_RES1,R5
01212c:   6216 04E8           ADDC.W  &MPY_32__Multiplier__32_Bit_Mode_RES2,R6
012130:   6217 04EA           ADDC.W  &MPY_32__Multiplier__32_Bit_Mode_RES3,R7
012134:   013F 0044           MOVA    0x0044(SP),R15
012138:   00AF 001F           ADDA    #0x0001f,R15
01213c:   44CF 0000           MOV.B   R4,0x0000(R15)
012140:   1084                SWPB    R4
012142:   44CF 0001           MOV.B   R4,0x0001(R15)
012146:   45CF 0002           MOV.B   R5,0x0002(R15)
01214a:   1085                SWPB    R5
01214c:   45CF 0003           MOV.B   R5,0x0003(R15)
012150:   46CF 0004           MOV.B   R6,0x0004(R15)
012154:   1086                SWPB    R6
012156:   46CF 0005           MOV.B   R6,0x0005(R15)
01215a:   47CF 0006           MOV.B   R7,0x0006(R15)
01215e:   1087                SWPB    R7
012160:   47CF 0007           MOV.B   R7,0x0007(R15)

EVM430-F6736.map.txt

Best Regards,

Ernest Cho

over 6 years ago

0 George Mock over 6 years ago

TI__Guru**** 243870 points

Even though I have to guess at a few things, I think I have a reasonable idea of what is happening. To directly address this issue, we must have a test case. Though I am confident we can limit what is in this test case to a point to where your customer is willing to submit it.

This statement ...

Ernest Cho said:
afe_data->V_RMS_Src += *(int64_t *)(&RES0);

... generates a large number of instructions. Thus, it must be the case that the type of V_RMS_Src is a complicated user defined class. This class includes a large function for the operator += . That being the case, there is no way we can reproduce this issue by guessing at the source code. A test case from the customer must be submitted, or nothing more can be done.

The key question appears to be: Why does this statement use out-of-line calls to the multiply function in the compiler RTS instead of using the HW multiply instruction? Once we have a test case, I am confident we can answer. It is a good guess that some change in the source code or build options would help. Or, perhaps a change in the compiler is needed.

Ernest Cho said:
I asked them to support source code but they can't due to the security issue.

I understand. But I think they will be pleasantly surprised at how little we need in the test case. For one thing, we do not need the entire project. For the one source file which contains the problem C++ statements, please submit a test case as described in the article How to Submit a Compiler Test Case. Note how you can use the option --preproc_only so comments are not in the file.

If even that is too much, consider this variation. Prior to preprocessing the source file, surround parts of the code which are unrelated like this ...

#if 0
/* unrelated code here */
#endif

Then perform the preprocessing step. The unrelated lines do not appear in the resulting preprocessed file. Make sure the problem assembly code is still generated.

Another step which may help ... Obfuscate the code. Performance an internet search on the term c++ code obfuscator, and use one of those tools.

Note the article says to attach the test case to a forum post. But you are welcome to send it to me by private message within the forum, or by email. No matter how you send it, be sure to include the compiler version and all the build options.

Thanks and regards,

-George

0 George Mock over 6 years ago in reply to George Mock

TI__Guru**** 243870 points

Please submit the requested test case.

Thanks and regards,

-George

0 George Mock over 6 years ago in reply to George Mock

TI__Guru**** 243870 points

Since it has been a while, I presume you have resolved your problem. I'd appreciate hearing how you resolved it.

Thanks and regards,

-George

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CCS/MSP430F6736A: [CCS] MPY command take too long cycle time for customer source code.