syntax and some other simple questions about spin

Comments

• bambino Posts: 789

  2007-04-06 18:16 edited 2007-04-06 18:16

  Rontopia,
  
  I don't have much time, but I'll answer as much as I can.
  #1 Outa is used to set the direction of a pin(or Pins). If you wish to know the state of a pin you must read it, to do that we must use the INA command. Some registers are read and write as you describe. These are not. The OUTA is writtable, where as the INA is only readable!
  
  #2 Yes, dira[noparse][[/noparse]x] := 1 and dira[noparse][[/noparse]x]~~ do the same function, and it may sound a bit redundant, but this is a nice feature to have when typing long programs(less Key strokes), and may be easier code to read for some programmers.
  
  #3 No, the ! operator is not a joke. If we explicitly set a bit to a one or a zero then we use dir[noparse][[/noparse]x] := 1 or dir[noparse][[/noparse]x] := 0. To do so with the not operator would mean we would have to know what the previous state of the pin was in order to get the out put we wanted. The not operator is handy when we don't really care what state the pin is, we just want it to change to the other state with minimal code. To do what the not operator does without useing it would require more code than just the one line.
  
  #4 is similiar to question one. the := operand is used to set(or write to) a variable or bit. The == operator is used to compare(or read) the value to its right with the value on its left. It does not set anything.
  
  I do not have a way of looking at the labs on this old win98 beast I'm useing, but I hope this helps!
  
  Cheers
  
  Sorry, missed one!
  
  [noparse]/noparse is used with arrays
  
  () is used with parameters
  
  Post Edited (bambino) : 4/6/2007 6:21:14 PM GMT
• Mike Green Posts: 23,101

  2007-04-06 18:22 edited 2007-04-06 18:22

  1) As is true of many microcontroller's I/O circuitry, there's a clear hardware existance for both a direction and an output register. In the case of the Propeller, the driver associated with each I/O pin can be set to output or input mode. If output mode, the actual state of the output is set by another signal provided by the output "register". If input mode, the actual state of the I/O pin is made available. The direction and output "register" for any given I/O pin is provided by some logic associated with each cog that ensures that the I/O pin has a determinable state based on all the cogs' actual registers, particularly if they are in conflict.
  
  If you will notice, there are 3 states involved for an I/O pin: driven to logic high, driven to logic low, and high impedance (input). That requires at least 2 bits, one from the direction register and one from the output register.
  
  2) The "~~" and "~" operators do the same thing effectively as using ":= 1" and ":= 0". They have some advantages when using them in expressions like "cog~ - 1" which has the value of "cog-1", but has the side effect of zeroing cog afterwards. You can't do that with the assignment operator.
  
  3) The "!" operator is a bit-wise not operator. If you say "outa[noparse][[/noparse]7] := !outa[noparse][[/noparse]7]" you are toggling or complementing that particular bit (setting it to its opposite state). You say "If I know that outa[noparse][[/noparse]pin] is set to 1". How do you know that? You could write this

  if outa[noparse][[/noparse]7] == 1
     outa[noparse][[/noparse]7] := 0
  

  
  
  but it wouldn't be the same as "outa[noparse][[/noparse]7] := !outa[noparse][[/noparse]7]" because the "if" statement doesn't account for the case where outa[noparse][[/noparse]7] is set to 0.
  
  4) ":=" is the assignment operator. It changes the value of the variable on the left side to the value of the expression on the right side. "==" is the equality operator. It has the value TRUE if the left expression is equal to the right expression and the value FALSE otherwise. They're completely different.
  
  5) Parentheses are used in parameter lists (like ButtonTime(pin)) and to group expressions within other expressions. The square brackets are used for array subscripts and things that behave like array subscripts (like bit numbers or bit group numbers ... like outa[noparse][[/noparse]7] or outa[noparse][[/noparse]4..7]).
  
  6) The colon in a method declaration separates the function prototype from the name of the return value. The default return value name is "result" and is present for all methods whether used or not. The colon allows you to substitute a more meaningful name, that's all. The vertical bar ("pipe") separates the function prototype or return name from a list of local variables all of which are longs.
• Rontopia Posts: 139

  2007-04-06 19:09 edited 2007-04-06 19:09

  thanks guys, you rock
  ok.. i think i get it.. let me ask this..

  ---

  PUB Blink (pin, rate, reps)
  ······ dira[noparse][[/noparse]pin]~~
  ······ outa[noparse][[/noparse]pin]~
  ··
  ······ repeat reps * 2
  ········ waitcnt(rate /2 + cnt)
  ········ !outa[noparse][[/noparse]pin]

  ---

  if I dont care what the begining state of outa is, do i have to set it with the ouat[noparse][[/noparse]pin]~ statment? in other words I could say

  ---

  PUB Blink (pin, rate, reps)
  ······ dira[noparse][[/noparse]pin]~~
  
  ······ repeat reps * 2
  ········ waitcnt(rate /2 + cnt)
  ········ !outa[noparse][[/noparse]pin]

  ---

  the !outa[noparse][[/noparse]pin] statment would just toggle the pin reguardless of its begining state? i do understand that this is not really a good idea, but all im trying to do here is understand the nature of the syntax and the registors
  

  Mike Green said...
  6) The colon in a method declaration separates the function prototype from the name of the return value. The default return value name is "result" and is present for all methods whether used or not. The colon allows you to substitute a more meaningful name, that's all. The vertical bar ("pipe") separates the function prototype or return name from a list of local variables all of which are longs.

  
  does colon = pipe here? maybe·I dont know what the proper name is? in unix we always called | a pipe operator.
  
  also, in the statment PUB Blink (pin, rate, reps), your saying that this will return a value which is called result even if I dont ask for it? if im understanding this right this means that Blink will = result? futthermore, if I wanted a result to be named something else and I want to manage that name/value, I would say something like PUB Blink someValue | (pin, rate, rate) ?
  
  
  I cant thank you guys enough for taking the time.
  
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  Muahdib
  
  
  IC layout designer
  Austin Texas
  
  Post Edited (Rontopia) : 4/6/2007 7:14:48 PM GMT
• Mike Green Posts: 23,101

  2007-04-06 19:16 edited 2007-04-06 19:16

  If you don't care about the initial state of OUTA, you can ignore it.
  
  Colon is the name for ":".
  
  If you do something with the value returned by blink, you'll notice that it's zero unless set to something else within blink. The Spin interpreter always initializes the value of result to zero.
• Rontopia Posts: 139

  2007-04-07 23:56 edited 2007-04-07 23:56

  thanks.. I thnk i got now
  
  if not I'll be back
  
  ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
  Muahdib
  
  
  IC layout designer
  Austin Texas