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Function with xfer name of Stream

 
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xtremeroboz



Joined: 15 Mar 2019
Posts: 1

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Function with xfer name of Stream
PostPosted: Fri Mar 15, 2019 1:49 am     Reply with quote

Hi Everyone

I try to create a function with xfer, this is part of my code:

Code:

#use spi (MASTER, CLK=SPI_CLOCK, DI=SPI_DATA, LOAD=SPI_LOAD, LOAD_ACTIVE=1, MODE=2, BITS=8, STREAM=SHIFT_REG_A, MSB_FIRST)
#use spi (MASTER, CLK=SPI_CLOCK, DI=SPI_DATA, LOAD=SPI_LOAD, LOAD_ACTIVE=1, MODE=1, BITS=8, STREAM=SHIFT_REG_B, MSB_FIRST)
#use spi (MASTER, CLK=SPI_CLOCK, DI=SPI_DATA, LOAD=SPI_LOAD, LOAD_ACTIVE=1, MODE=0, BITS=8, STREAM=SHIFT_REG_C, MSB_FIRST)

//This is My Function
unsigned int ReadShiftRegister(char NUM_SHIFT_REGISTER)
{
unsigned int VAL_SHIFT_REGISTER;
   
VAL_SHIFT_REGISTER = spi_xfer(NUM_SHIFT_REGISTER, 0x00);

return VAL_SHIFT_REGISTER;
}


I have trouble with variable NUM_SHIFT_REGISTER

*** Error 130 "shifts.c" Line 315(51,55): Stream must be a constant in the valid range ::


Thanks for your help
Ttelmah



Joined: 11 Mar 2010
Posts: 14303

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PostPosted: Fri Mar 15, 2019 3:20 am     Reply with quote

The point is that stream names _have to be constants_.
If you want to use a variable, you have to code this yourself.
Understand that when a stream name is used for a function like SPI_XFER,
the code to physically access the named stream is substituted.

So if you want to use a variable to access three different streams, you
would have to just use a variable, and a switch statement to call the
three different output routines. So:
Code:

//This is My Function
unsigned int ReadShiftRegister(char NUM_SHIFT_REGISTER)
{
   unsigned int VAL_SHIFT_REGISTER;
   switch (NUM_SHIFT_REGISTER) {
   case 0:
       VAL_SHIFT_REGISTER = spi_xfer(SHIFT_REG_A_REGISTER, 0x00);
       break;
   case 1:
       VAL_SHIFT_REGISTER = spi_xfer(SHIFT_REG_B_REGISTER, 0x00);
       break;
   case 2:
       VAL_SHIFT_REGISTER = spi_xfer(SHIFT_REG_B_REGISTER, 0x00);
       break;
   }
   return VAL_SHIFT_REGISTER;
}


As a general 'style comment', in C, it is standard to reserve 'ALL CAPITALS'
for things that are #defined, or otherwise fixed (so typedefs for example).
So better to call a variable that accesses a shift register number
'Val_Shift_Register'.
As a standard, it helps when debugging code, to quickly be able to
distinguish things that are variables from things that are not.
Just a useful 'tip' to help code legibility.
dluu13



Joined: 28 Sep 2018
Posts: 166
Location: Toronto, ON

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PostPosted: Fri Mar 15, 2019 8:05 am     Reply with quote

Ttelmah wrote:
As a general 'style comment', in C, it is standard to reserve 'ALL CAPITALS'
for things that are #defined, or otherwise fixed (so typedefs for example).


This is important, especially when #case is used. I had a bunch of stream names stop working suddenly when I added #case. Apparently the compiler capitalized the stream names.
Ttelmah



Joined: 11 Mar 2010
Posts: 14303

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PostPosted: Fri Mar 15, 2019 8:53 am     Reply with quote

Yes, the one for streams is very important. CCS defaults internally to
capitalising all stream names, and if you implement #case, and use a
stream name that is not capitalised, it won't work...
temtronic



Joined: 01 Jul 2010
Posts: 6658
Location: Greensville,Ontario

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PostPosted: Fri Mar 15, 2019 1:12 pm     Reply with quote

BTDT,, got stumped for quite awhile..... Sad
Jay
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