Bitwise, Shifting, return value and call prob

[Nobody/Anonymous]

Dear Mr Hugh Considine,
I really enjoy your great cow Basic work, and actually I'm having some problem that I really dont know who to address to. I hope u would take some of ur busy valuable time out n help me to sort this out, cuz actually my work is due by 16/03 :( so that u can save a life :).
Anyway thanx alot Hugh for creating this compiler great work, this is d question I would like to ask:
This is d C code that I would like to translate into GCBASIC, (This one is used for controlling I2C
bit i2c_tx(unsigned char d)
{
char x;
static bit b;
  for(x=8; x; x--) {
    if(d&0x80) SDA = 1;
    else SDA = 0;
    SCL = 1;
    d <<= 1;
    SCL = 0;
  }
  SDA = 1;
  SCL = 1;
  i2c_dly();
  b = SDA_IN;          // possible ACK bit
  SCL = 0;
  return b;
}
And this is how I converted:
Sub i2c_tx(d as byte)
dim x as word;
dim b bit;
  for x = 8 to 0[step -1]
    if d&0x80 then set SDA ON
    set SDA OFF
    Set SCL ON
    Rotate d Left
    set SCL OFF
    loop
  set SDA ON
  set SCL ON
  wait 2 us
  b = SDA_IN;          // possible ACK bit
  set SCL OFF
  return b
End Sub
There's a few of them I dont noe how to convert like: AND the byte together, shifting i used rotate is it correct?,  return d value and call this subroutine function out i use: Goto i2c_tx(0xBD) with the variable inside d bracket
Pls let me noe what do u think
Thanx alot :) Have a great day... n Thanx for ur great work. Really save me alot of time n effort :)

[Hugh Considine]

Here's how I translated it:
Function i2c_tx(data)
   
    for x = 8 to 0
        if data.7 = 1 Then
            SDA = 1
        else
            SDA = 0
        End If
        SCL = 1
        Set STATUS.C Off
        Rotate data Left
        SCL = 0
    Next
    SDA = 1
    SCL = 1
    wait 2 us
    i2c_tx = SDA_IN ' possible ACK bit
    SCL = 0
   
End Function

There isn't any need to declare the variables, as GCBASIC declares byte variables automatically. It's also quicker to use byte variables than bit variables, even though doing so wastes a small amount of RAM.

GCBASIC will step backwards if both the start and end value are constants, and the end value is less than the start value. Otherwise, use step but note that it has no brackets.

The And is used to check bit 7. Anding with 0x80 clears all bits except bit 7. C treats anything non-zero as true, so the result of the if depends on bit 7.

You missed the else in the if - this is needed to stop the data pin getting turned on and then off again straight away.

Rotate is correct, but in GCBASIC you need to clear status bit C to stop it from getting rotated into the end of the variable.

Next matches the end of a For loop, not Loop. Next and Loop are the odd ones, everything else is End ... (End Sub, End If, End Repeat, etc).

Return in GCBASIC currently doesn't actually allow for returning values, it's used to return from Gosub. I'm planning on changing this at some stage in the future. To return a value, set the variable with the same name as the function.

To call the sub, you don't need Goto. Just the name of the sub, and then any parameters. The parameters can be in brackets, but they're not needed. Separate multiple parameters with commas.

Also, it's not usually good to use single letter variable names. There are a many bits in the PIC which have single letter names (C and Z come to mind, there are others), and GCBASIC will get confused if there is a variable with the same name. I've changed to d to data, but I've not changed x as I can't think of any bits in the PIC with this name. However, if GCBASIC complains you'll need to change it to something a bit longer.

There are also some software I2C routines already written for GCBASIC, they're in one of the posts in https://sourceforge.net/forum/forum.php?forum_id=629990