I have a thought that would make many processes much more effective and, being only one voice, I would like to know if there is a demand before I propose it to Keil. This is the result of me having to change a switch statement to a series of IFs to make an ISR process fast enough. I realize, and thus do not complain, that Keil caould not implemet an ANSI-C switch more efficient than the way it is done. 'n' below will be either 2 or 3 (if Keil decide to implement, they can choose) a Proposal: if #pragma QUICKSWITCH then a) no case value can be more than 255 b) all case values must be multiples of n c) the switch will be implemented as a jump table Erik
Eric, just a thought to avoid the ccase: the above code should result in code without calling the cccase. Thats my trick to work around your proposal. ??? I have no problem with the call to ccase, I want it, it is a debug catcher for 'impossible' conditions. What I want is a JUMP TABLE instead of the cumbersome code for the 'flexible' switch statement. Erik
sorry, ccase you refer to is the Keil switch subroutine? I have a similarily named flycatcher. Are you, in effect, saying that the jump table is implemented if there is no default: in the code, that is a BUG!. Erik
I took out the default: and ?C?CCASE is still called. Erik
getting late, I now see the 'return', I included it to the below and ?C?CCase is still called. what is different from what you show?
367 //////////////////////////////////////////////////////////// 368 // 369 // ISR 14: void ISR_T3 (void) 370 // 371 372 void ISR_T3 (void) interrupt 14 using 1 373 { 374 1 SB1_TMR3CN_TR = 0; 375 1 SB1_TMR3CN_TF = 0; 376 1 switch (GC4holdState) 377 1 { 378 2 case G4HS_IDLE: // 0x00 should never happem 379 2 catchT3(0x01); 380 2 // break; 381 2 return; 382 2 383 2 case G4HS_RCDN: // 0x01 receive complted now processing 384 2 SBG_P0_D485 = 1; 385 2 SG_SFRPAGE = 0; 386 2 SB0_SCON0_TB8 = 1; 387 2 S0_SBUF0 = RSP_BUSY; 388 2 // break; 389 2 return; 390 2 391 2 case G4HS_RCCM: // 0x02 processing of receive complted 392 2 SBG_P0_D485 = 1; 393 2 SG_SFRPAGE = 0; 394 2 SB0_SCON0_TB8 = 1; 395 2 S0_SBUF0 = RSP_CMPL; 396 2 GC4holdState = G4HS_RCHO; 397 2 // break; 398 2 return; 399 2 400 2 case G4HS_RCER: // 0x03 receive complted, error detected, record ignored 401 2 SBG_P0_D485 = 1; 402 2 SG_SFRPAGE = 0; 403 2 SB0_SCON0_TB8 = 1; 404 2 S0_SBUF0 = RSP_ERR; 405 2 GC4holdState = G4HS_RCHO; 406 2 // break; 407 2 return; 408 2 409 2 case G4HS_RCHO: // 0x04 receive response completed hold off switch to receive 410 2 SBG_P0_D485 = 0; // now back to receive 411 2 GC4holdState = G4HS_IDLE; // no response cycle in progress 412 2 GCI4xferSt = I4_IDLE; // new interrupt sequence 413 2 // break; 414 2 return; 415 2 416 2 // default: 417 2 // catchT3(0xff); 418 2 // break; 419 2 420 2 } 421 1 } ; FUNCTION ISR_T3 (BEGIN) 0000 C0E0 PUSH ACC 0002 C083 PUSH DPH 0004 C082 PUSH DPL 0006 C0D0 PUSH PSW 0008 75D008 MOV PSW,#08H ; SOURCE LINE # 372 ; SOURCE LINE # 374 000B C2CA CLR SB1_TMR3CN_TR ; SOURCE LINE # 375 000D C2CF CLR SB1_TMR3CN_TF ; SOURCE LINE # 376 000F E500 E MOV A,GC4holdState 0011 120000 E LCALL ?C?CCASE
I took out the default: and ?C?CCASE is still called. even on OT(8)? here that works Thomas
NO, NO WAY I have NO INTENTION of screwing up my debugging capabilities by optimizing beyond object = source. Erik
I have to agree with Erik on this one. Jump tables and their assocaited jmp @a+dptr are a fundamental instruction in the 51 for achieving efficiency, particularly within interrupts where the desire is to keep processing time to a minimum. However, I don't see why a pragma would even be necessary. Let's assume the pragma is implemented, but the code violates the required case values (i.e. byte size, increments of 2 or 3). In this case, the compiler's going to have to validate the case values to ensure compliance with the pragma anyway, so why not simply have the compiler check for "jump table possible" case values and render a direct jump table if found ???
I have to agree with Erik on this one. thanks However, I don't see why a pragma would even be necessary The advantage of a #pragma as I see it would be that you effectively told the compiler "tell me if you can not do this". If an 'automatic' were implemented, you would never know (except through investigating the assembler) if you had achieved the goal. Of course, a possibility would be a #pragma TELL_IF_SWITCH_CAN_NOT_BE_JUMP_TABLE which would satisfy both approaches. Anyhow, I STILL can not see why this has anything to do with optimization. as I see it, the compiler should do the best it can without disrupting the flow, and leave 'worthless' statements (inserted to provide a breakpoint opportunity) in the code. Then, if desired, optimization (which may/should disrupt the flow and skip dead code) can be implemented. Using jump tables has NOTHING to do with optimization (except to make the result of optimizing look better) Erik
The advantage of a #pragma as I see it would be that you effectively told the compiler "tell me if you can not do this". If an 'automatic' were implemented, you would never know (except through investigating the assembler) if you had achieved the goal. Good point. And I agree, the compiler should take every opportunity, regardless of OT level, to leverage direct jump tables if possible...IMO ;)