Why can't I get Serout to work

SailerMan · 2006-10-07 13:58

I have my encoders working and now I want to get the counts to my "Propeller".· If I send 2400 Baud from my Stamp2 for instance·the propeller gets the data·perfectly, but when I send them from my SX/B program I can't get it to work.

I know it has something to do with the interrupts, but I'm not really versed on how to calculate the Clock cycles it consumes.

How would I calculate a baud rate that will actually send 2400?

DEVICE          SX28, OSCHS2, TURBO, STACKX, OPTIONX, BOR42
FREQ            50_000_000
ID  "ENCODER"
EncPort         VAR     RA                      ' encoder port
TRIS_Enc        VAR     TRIS_A
MaxVal          CON     255
 
'encCheck VAR Byte
EncodersOld     VAR     byte                  
EncodersNew     VAR     byte                   
Encoder_A_Count VAR     byte  
Encoder_B_Count VAR     byte   
tmpB1           VAR     byte
tmpB2           VAR     Byte
tmpB3           VAR     Byte
' =========================================================================
INTERRUPT 
' =========================================================================
' Runs every 64 uS @ 4 MHz (no prescaler)
ISR_Start:
 EncodersNew = EncPort
 TmpB1 = EncodersOld XOR EncodersNew ' compare old with new
                                     ' to work out which channels have changed
 TmpB2 = TmpB1 << 1   ' make single bit that shows change on A or B phase
 TmpB1 = TmpB1 OR TmpB2
 EncodersOld = EncodersOld << 1  ' make direction bits by comparing old A with new B
 EncodersOld = EncodersOld XOR EncodersNew ' xor old A with new B
 IF TmpB1.3 = 1 THEN
     IF EncodersOld.3 = 1 THEN 
   INC Encoder_A_Count                          
     ELSE
   DEC Encoder_A_Count 
 Encoder_A_Count Min 0                           
      ENDIF
  ENDIF
' ========================================================================= 
 IF tmpB1.1 = 1 THEN                  
      IF EncodersOld.1 = 1 THEN 
     INC Encoder_B_Count                          
      ELSE
   DEC Encoder_B_Count 
 Encoder_B_Count Min 0                           
      ENDIF
   ENDIF
 EncodersOld=EncodersNew
'ISR_Exit:
  RETURNINT                                  
' =========================================================================
  PROGRAM Start NOSTARTUP
' =========================================================================
 
Start:
                              
 
  EncodersNew = EncPort
  EncodersOld = EncodersNew
  Encoder_A_Count = 0 
  Encoder_B_Count = 0 
   
  OPTION = $88                                  ' interrupt, no prescaler
Main:
Do
  Serout RC.7,T2400,Encoder_A_Count
 
LOOP

Thanks,
Eric

Sparks-R-Fun · 2006-10-07 21:17

Eric,

It seems that what you are trying to attempt may be rather tricky. If your ISR was designed such that each and every time it was called it took exactly the same number of clock cycles to complete, then the solution might be as easy as adjusting the effective frequency passed to the compiler. The compiler would then make adjustments to the serout routine so that the internal timing would work out correctly. Unfortunately, your ISR seems to be capable of taking variable length paths based upon encoder information and that can not be completely predicted and taken into account.

Some Considerations
1) Given that 2400 baud is such a slow baud rate, have you confirmed that it is indeed the ISR that is causing your problem? If you disable interrupts, is data transmitted correctly?

2) Have you considered using a synchronous serial transfer like the one provided by the 'shiftout' command? Granted, it will require the use of one or two additional pins, but the advantage of a synchronous transfer is that the clock rate can vary a great deal without affecting the data being sent.

Those are just some thoughts I had.

Bean · 2006-10-07 22:11

Eric,
An easy "cheat", is to just increase the baud rate until it starts working, then keep increasing it until it stops working again. Then use the average of those two values.

For instance if it starts working at T2800 then stop working again at T3200, just use T3000 for the baud rate.

Bean.

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Low power SD Data Logger www.sddatalogger.com
SX-Video Display Modules www.sxvm.com

Don't mistake experience for intelligence. And vis-vera.
·

SailerMan · 2006-10-09 11:38

AH!!! Well, I got the propeller to receive 9600 baud by using 7200 Baud on the propeller.

One thing I can't do is find what Baud I need to send to the SX28, I tried 7200 but It does not work... this trial and Error is not going well.

Let's say I am sending from the SX28 N9600... Under normal conditions how do I calculate the Pulse width of each bit in microsecs. I figure once I know that·I can measure and compare it on my USB Scope.

I need to figure out a fool proof method of being able to send a serial command to the SX28 and it respond correctly every time. I'm going to use one for My Encoders and a couple of other Tasks.

·

Bean · 2006-10-09 12:48

Eric,
Since the interrupt is making the SX send bits SLOWER, you need specify a higher baud rate.
To send on the SX try using 12800 baud (or there-abouts) that should send at about 9600 baud.

The pulse width is simple 1/baud seconds. So 9600 baud would be 1/9600 = 104.16uSec per bit.

At 50MHz your interrupt is occuring every 5.12uSec, so there will be about 20 interrupts per bit (that is a GOOD thing). The more interrupts per bit, the more consistance they will be with the "fudge-factor".

What is going to hurt your timing is that your interrupt does NOT take the same·number of cycles each time.

Bean.

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Post Edited (Bean (Hitt Consulting)) : 10/9/2006 12:57:21 PM GMT

pjv · 2006-10-09 15:42

Hi Eric;

If you were to write this encoder and UART code in assembler, then it is relatively easy to have multiple timed tasks not interfering with each other. Using a simple task scheduler, the encoder and communication routines can be written to be totally indendent of each other.

The downside is that it is quite a bit more work as compared to using SX/B, but the upside is that it works without fail, and is easier to debug with the SX-Key.

Eventhough it is more work, I don't want to suggest that it is a daunting task.... just more work than SX/B.

If you think this might be an eventual approach for you, I'd be happy to give you some pointers and help you through it.

Cheers,

Peter (pjv)

SailerMan · 2006-10-09 16:18

Well Since I don't have any experience in Assembler I'd have to learn a whole new language.

It's funny... I can write programs to make a 3D Lunar Lander (Remake) but I can't make a microcontroller to a simple serial transfer.

I guess I should have learned ASM!!!

Anyhow... Bean... If I put delays in my code above for instance...

IF TmpB1.3 = 1 THEN
     IF EncodersOld.3 = 1 THEN 
        INC Encoder_A_Count                          
     ELSE
        DEC Encoder_A_Count 
     ENDIF
ELSE   
   ASM 
     NOP
     NOP
     NOP
     NOP
   END ASM
EndIF
' ========================================================================= 
 IF tmpB1.1 = 1 THEN                  
      IF EncodersOld.1 = 1 THEN 
         INC Encoder_B_Count                          
      ELSE
         DEC Encoder_B_Count 
      ENDIF
 ELSE   
   ASM 
     NOP
     NOP
     NOP
     NOP
   END ASM
ENDIF
If not Tmpb1.1<>1 and Tmpb1.3<>1
 '----------------------------------  Delay twice as long
   ASM 
     NOP
     NOP
     NOP
     NOP
     NOP
     NOP
     NOP
     NOP
   END ASM
End if

Will this help even out the timing issues??

Peter (pjv)

I would appreciate any help you can offer.· (THANKS!!! )

Best Regards,

Eric

Rsadeika · 2006-10-09 16:40

Eric,

I found working with interrupts within SX/B to be a major headache. You may want to goto the help file and re-read all the commands that will be affected by using·an interrupt. I believe that serin/out is one that gets affected by·using an interrupt. Now, somewhere in my reading it states that you can overcome this by turning the interrupt on and off, boy doesn't that sound like easy coding.

If you really are serious with your project, I would take up the offer that Peter (pjv) just made you. But keep in mind that his tutaledge will be in asm, and not in SX/B.

Ray

pjv · 2006-10-09 18:29

Hi Eric;

SX/B compiles to assembler (this is very useful for understanding and debugging), so I took your code and compiled and analyzed it.

The following numbers have some approximations due to rounding.

The encoder code in the interrupt routine consumes 72, 76 or 80 clock cycles, depending on what branches it follows.

At 2400 baud, the serial routine should output a bit every 416.6 uSec. Considering the interrupt is triggered every 256 clocks, which is 5.12 uSec, therefore the interrupt routine is executed 416.6 / 5.12 = 81.4 (use 81) times per transmitted bit. This means the interrupt activity eats up 81 times 72, 76 or 80 clocks, and that is works out to 5832, 6156 or 6480 clocks, which translates to 117, 123 or 130 uSec.

That implies the effective time for serial comms bits must be adjusted by those amounts to become 417 minus (117, 123 or 130) resulting in 300, 294 or 287 uSec. And these times would translate to (baud=1/time) 3333 baud, 3401 baud or 3484 baud, again depending on the path taken through the interrupt routine.

The extremes represent a variance of about 2 percent from the middle, and that should be well within the acceptance band of the serial receiver. So I suggest you try perhaps the middle one of those numbers and tell us what happens.

Cheers,

Peter (pjv)

SailerMan · 2006-10-09 19:57

Wow Peter now that is something I can use. How the heck did you figure out how many clock cycles it took?

Would adding NOP statements like I listed above help even out the Interupt time?

Now if I am Recieving a serial Stream from my propeller that is 2400 Baud would I still used the same Baud rate of (3401) on the SX28?

Can I use the same logic on 9600 Baud? I came up with an effective rate of 13557.

Thanks for staying with me. [noparse]:)[/noparse]

pjv · 2006-10-09 20:59

Hi Eric;

You have several questions here, so let me try:

1. Simply draw a little flow chart of the assembly equivalent of the SX/B ISR code, and count the respective number of machine cycles for each native (NOT compound) instructions. Also allow 3 each for getting into and out of the interrupt. There are actually 6 possible paths through your ISR routine, but several of them happen to have the same count.

2. I did not analyze your no-op approach, so I can't really comment. It would depend what paths they ended up in. It might be that it's not (easily) possible.

3. I have not analyzed the assembler equivalent of the SX/B serial receive code, so again it's hard for me to say for sure, but I have a suspicion that it may be so.

4. I believe so. You might be better to use the average of the two extremes which I calculated to be 13,333 and 13889, so I would use 13,611. Try it and see if it works.

Glad to be able to help.

You know, it would be great if SX/B could run in a non-blocking mode and let more than one thread run at a time; I wonder.......

Cheers,

Peter (pjv)

SailerMan · 2006-10-10 12:05

Works Like a charm!! thanks again.

OK next question.
Are there any problems with the Serin Command?

I·added some code..

Main:

Do

Serin RC.7,N13611,Command,500,Pass

Pause 25

Serout RC.7,N13611,"!"  '----- (222)

SerOut RC.7,N13611,Encoder_A_Count

Loop

PASS:

Serout RC.7,N13611,Command

Goto Main

The above is just a snipet...

What I do is send a Character from my "Propeller"

If the SX recieves that character it outputs the Encoder count.

What is happening is the SERin is Timing out and the SX outputs the Command variable which happens to be what I am sending to it. My question is ... how can Serin time out and the Command Variable contain serial data from the host??

Bean · 2006-10-10 13:09

When the SERIN times-out, it does not affect the value of "command". So it will still contain whatever it had before the SERIN command.

Bean.

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Low power SD Data Logger www.sddatalogger.com
SX-Video Display Modules www.sxvm.com

Don't mistake experience for intelligence. And vis-vera.
·

SailerMan · 2006-10-10 14:22

I would think that "Command" Would be Zero but instead it is equal to the byte I send via the Propeller... I better recheck my code and setup before I ask too many more questions. [noparse]:)[/noparse]

Why can't I get Serout to work

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