ECE/CE 3720: Embedded System Design

Transcription

1 Produce-Consumer Examples Slide 1 ECE/CE 3720: Embedded System Design Chris J. Myers Slide 3 Source/producer Keyboard input Program with data Sink/consumer Program that interprets Printer output Lecture 7: FIFOs Program sends message Program receives message Microphone and ADC Program that saves sound data Program that has sound data DAC and speaker Introduction to FIFOs Two-Pointer FIFO FIFO circular queue is useful for a buffered I/O interface. This order-preserving data structure temporarily saves data created by producer before processed by consumer. Slide 2 Decouples the producer from the consumer. Use statically allocated global memory, so they can be shared by threads, but must be accessed carefully. Slide 4 (See Figures 4.15 and 4.16) (See Figure 4.13) 1 2

2 Slide 5 Basic Idea of FIFO GetPt rmb 2 Ptr to oldest data, next to be removed PutPt rmb 2 Ptr to free memory, place to put next * Reg A contains byte to store into the FIFO PutFifo ldx PutPt Reg X points to free place staa,x Store data into FIFO inx Update pointer * Reg A returned with byte from FIFO GetFifo ldx GetPt Reg X points to oldest data ldaa,x Read data from FIFO inx Update pointer stx GetPt Slide 7 Initialization of a Two-Pointer FIFO in Assembly FifoSize equ 10 Size of Fifo PutPt rmb 2 Pointer where to put next */ GetPt rmb 2 Pointer where to get next * FIFO is empty if PutPt=GetPt * FIFO is full if PutPt+1=GetPt (with wrap) Fifo rmb FifoSize The fifo data InitFifo ldx #Fifo tpa sei entering critical section stx GetPt Empty when PutPt=GetPt tap end critical section Initialization of a Two-Pointer FIFO in C PutFifo for a Two-Pointer FIFO in C Slide 6 #define FifoSize 10 /* Size of Fifo */ char *PutPt; /* Ptr of where to put next */ char *GetPt; /* Ptr of where to get next /* FIFO is empty if PutPt=GetPt */ /* FIFO is full if PutPt+1=GetPt (with wrap) */ char Fifo[FifoSize]; /* The fifo data */ void InitFifo(void) { char SaveSP; asm(" tpa\n staa %SaveSP\n sei"); /* critical */ PutPt=GetPt=&Fifo[0]; /* Empty when PutPt=GetPt */ Slide 8 int PutFifo (char data) { char *Ppt; char SaveSP; asm(" tpa\n staa %SaveSP\n sei"); /* critical */ Ppt=PutPt; /* Copy of put pointer */ *(Ppt++)=data; /* Put data into fifo */ if (Ppt == &Fifo[FifoSize]) Ppt = &Fifo[0]; if (Ppt == GetPt ) { return(0); /* Failed, fifo was full */ PutPt=Ppt; return(-1); /* Successful */ 3 4

3 Slide 9 PutFifo for a Two-Pointer FIFO in Assembly * Input RegA contains 8 bit data to put * Output RegA is -1 if successful, 0 otherwise PutFifo psha tpa tab pshb save old CCR sei critical section ldx PutPt Temporary put pointer staa 0,x Try to put data into fifo inx cpx #Fifo+FifoSize Slide 11 GetFifo for a Two-Pointer FIFO in C int GetFifo (char *datapt) { char SaveSP; if (PutPt == GetPt ) { return(0); /* Empty if PutPt=GetPt */ *datapt=*(getpt++); if (GetPt == &Fifo[FifoSize]) GetPt = &Fifo[0]; return(-1); PutFifo for a Two-Pointer FIFO in Assembly GetFifo for a Two-Pointer FIFO in Assembly Slide 10 bne PutNoWrap skip if no wrap needed ldx #Fifo Wrap PutNoWrap clra assume it will fail cpx GetPt Full if now the same beq PutDone coma RegA=-1 means OK PutDone tab end critical section Slide 12 * Input RegX points to place for 8 bit data * Output RegA is -1 if successful, 0 if Fifo empty GetFifo tpa psha save old CCR sei critical section clra assume it will fail ldy GetPt cpx PutPt Empty if initially same beq GetDone coma RegA=-1 means OK ldab 0,y Data from FIFO stab 0,x Return by reference iny 5 6

4 Initialization of a Two-Ptr/Cnt FIFO in Assembly Slide 13 GetFifo for a Two-Pointer FIFO in Assembly cpy #Fifo+FifoSize bne GetNoWrap skip if no wrap needed ldy #Fifo Wrap GetNoWrap sty GetPt GetDone tab end critical section Slide 15 FifoSize equ 10 Size of Fifo PutPt rmb 2 Pointer of where to put next GetPt rmb 2 Pointer of where to get next Size rmb 1 Fifo rmb FifoSize fifo data InitFifo tpa sei critical section ldx #Fifo stx GetPt Empty when Size == 0 clr Size tap end critical section Initialization of a Two-Pointer/Counter FIFO in C PutFifo for a Two-Pointer/Counter FIFO in C Slide 14 #define FifoSize 10 /* Size of Fifo */ char *PutPt; /* Ptr of where to put next */ char *GetPt; /* Ptr of where to get next */ unsigned char Size; /* # of elements in FIFO */ /* FIFO is empty if Size=0 */ /* FIFO is full if Size=FifoSize */ char Fifo[FifoSize]; /* fifo data */ void InitFifo(void) { char SaveSP; PutPt=GetPt=&Fifo[0]; /* Empty when Size==0 */ Size=0; Slide 16 int PutFifo (char data) { char SaveSP; if (Size == FifoSize ) { return(0); /* Failed, fifo was full */ Size++; *(PutPt++)=data; /* put data into fifo */ if (PutPt == &Fifo[FifoSize]) PutPt = &Fifo[0]; return(-1); /* Successful */ 7 8

5 PutFifo for a Two-Ptr/Cnt FIFO in Assembly GetFifo for a Two-Pointer/Counter FIFO in C Slide 17 * Input RegA contains 8 bit data to put * Output RegA is -1 if successful, 0 otherwise PutFifo psha tpa tab pshb save old CCR sei critical section ldab Size cmpb #FifoSize Full if Size==FifoSize bne PutNotFull clra bra PutDone Slide 19 int GetFifo (char *datapt) { char SaveSP; if (Size == 0 ){ return(0); /* Empty if Size=0 */ *datapt=*(getpt++); Size--; if (GetPt == &Fifo[FifoSize]) GetPt = &Fifo[0]; return(-1); Slide 18 PutFifo for a Two-Ptr/Cnt FIFO in Assembly PutNotFull incb stab Size Size++ ldx PutPt staa 0,x Put data into fifo inx cpx #Fifo+FifoSize bne PutNoWrap skip if no wrap needed ldx #Fifo Wrap PutNoWrap ldaa #-1 success means OK PutDone tab end critical section Slide 20 GetFifo for a Two-Ptr/Cnt FIFO in Assembly * Input RegX points to place for 8 bit data * Output RegA is -1 if successful, 0 if Fifo empty GetFifo tpa psha save old CCR sei critical section clra assume it will fail tst Size beq GetDone dec Size ldy GetPt coma RegA=-1 means OK ldab 0,y Data from FIFO stab 0,x Return by reference 9 10

6 Initialization of a Index FIFO in Assembly Slide 21 GetFifo for a Two-Ptr/Cnt FIFO in Assembly iny cpy #Fifo+FifoSize bne GetNoWrap skip if no wrapping needed ldy #Fifo Wrap GetNoWrap sty GetPt GetDone tab end critical section Slide 23 FifoSize equ 10 Number of 8 bit data in Fifo PutI rmb 1 Index of where to put next GetI rmb 1 Index of where to get next Size rmb 1 * FIFO is empty if Size=0 * FIFO is full if Size=FifoSize Fifo rmb FifoSize fifo data InitFifo tpa sei entering critical section clr PutI clr GetI clr Size Empty when Size == 0 tap end critical section Initialization of a Index FIFO in C PutFifo for a Index FIFO in C Slide 22 #define FifoSize 10 /* Size of Fifo */ unsigned char PutI; /* Index where to put next */ unsigned char GetI; /* Index where to get next */ unsigned char Size; /* # of elements in FIFO */ /* FIFO is empty if Size=0 */ /* FIFO is full if Size=FifoSize */ char Fifo[FifoSize]; /* fifo data */ void InitFifo(void) {char SaveSP; PutI=GetI=Size=0; /* Empty when Size==0 */ Slide 24 int PutFifo (char data) { char SaveSP; if (Size == FifoSize ) return(0); /* Failed, fifo was full */ Size++; Fifo[PutI++]=data; /* put data into fifo */ if (PutI == FifoSize) PutI = 0; /* Wrap */ return(-1); /* Successful */ 11 12

7 Slide 25 PutFifo for a Index FIFO in Assembly * Input RegA contains 8 bit data to put * Output RegA is -1 if successful, 0 otherwise PutFifo psha tpa tab pshb save old CCR sei entering critical section ldab Size cmpb #FifoSize Full if Size==FifoSize beq PutNotFull clra bra PutDone PutNotFull incb stab Size Size++ ldx #Fifo Slide 27 GetFifo for a Index FIFO in C int GetFifo (char *datapt) { char SaveSP; if (Size == 0 ) return(0); /* Empty if Size=0 */ *datapt=fifo[geti++]; Size--; if (GetI == FifoSize) GetI = 0; return(-1); Slide 26 PutFifo for a Index FIFO in Assembly ldab PutI abx staa 0,x Put data into fifo incb cmpb #FifoSize bne PutNoWrap skip if no wrap needed clrb Wrap PutNoWrap clra sucess coma RegA=-1 means OK stab PutI PutDone tab end critical section Slide 28 GetFifo for a Index FIFO in Assembly * Input RegX points to place for 8 bit data * Output RegA is -1 if successful, 0 if Fifo empty GetFifo tpa psha save old CCR sei entering critical section clra assume it will fail tst Size beq GetDone ldy #Fifo ldab GetI aby coma RegA=-1 means OK ldab 0,y Data from FIFO 13 14

8 GetFifo for a Index FIFO in Assembly Slide 29 stab 0,x Return by reference ldab GetI incb cmpb #FifoSize bne GetNoWrap skip if no wrap needed clrb Wrap GetNoWrap stab GetI GetDone tab end critical section FIFO Dynamics Rates of production/consumption vary dynamically. t p is time b/w PutFifo calls, r p is arrival rate (r p = 1 t p ). t g is time b/w GetFifo calls, r g is service rate (r g = 1 t g ). Slide 30 If min t p max t g, FIFO is not necessary. If arrival rate can temporarily increase or service rate temporarily descrease, then a FIFO is necessary. If average production rate exceeds average consumption rate (i.e., r p > r g ), then FIFO will overflow. A full error is serious because if ignored data is lost. An empty error is usually not serious. 15