How to retrieve global variable values from VAR block inside DAT block.
Nicopowers
Posts: 12
Greetings Parallax Forum,
I am trying to constantly use a new and updated global variable inside the DAT block; however, when I try to reference that global variable, I get an error that says "Expected a constant, unary operator, or "("" below, I have the code that gives me the error:
As you can see, I am trying to use the global variable "Frequenz" that I initialize in PUB main, and then passing that value to "Delay" to then be used inside my loop that resides inside the DAT block. I have experience programming in SPIN Language, but I am not familiar with the Assembly environment. Is there a way to possibly read the data from the global variable via. it's memory address? Is there a semantic/syntactical solution to this? Any help will be much appreciated, thank you so much!
I am trying to constantly use a new and updated global variable inside the DAT block; however, when I try to reference that global variable, I get an error that says "Expected a constant, unary operator, or "("" below, I have the code that gives me the error:
CON
_CLKMODE = xtal1 + pll16x ' System clock --> 80 MHz
_XINFREQ = 5_000_000
MY_LED_PIN = 17 'this variable is used for the designation of the PIN to be toggled
VAR
long Divider, Frequenz
OBJ
pst : "Parallax Serial Terminal"
PUB main
Frequenz := 4000000
cognew(@blink, 0) 'Start a Cog with our assembly routine, no stack
'is required since PASM requires we explicitly
'assign and use memory locations within the Cog/Hub
' Divider = 0
' repeat 10
' Divider ++
DAT
'Step 1 of 3: --> This is the Assembly Code
org 0
blink mov dira, Pin 'Set our Pin to an output
'rdlong Delay, #0 'Prime the Delay variable with memory location 0
' shr Delay, #2 'important --> Divide by value indicated after "#"
'this is where the Propeller stores the CLKFREQ variable
'which is the number of clock ticks per second
mov Time, cnt 'Prime our timer with the current value of the system counter
add Time, #9 'Add a minimum delay (more on this below)
:loop waitcnt Time, Delay 'Start waiting
xor outa, Pin 'Toggle our output pin with "xor"
jmp #:loop 'Jump back to the beginning of our loop
' Step 2 of 3: --> Initialization of Symbolic Data
Pin long |< MY_LED_PIN 'Encode MY_LED_PIN to a bit mask --> Other alternative Pin long $0000_0010 Answer: Use I/O pin 4($10 or %1_0000)
'Pin long $0000_0000 '--> not used
Delay long Frequenz 'clock cycles to delay
Delay res 1 'Step 3 of 3: --> Reserved symbolic memory
Time res 1
fit
As you can see, I am trying to use the global variable "Frequenz" that I initialize in PUB main, and then passing that value to "Delay" to then be used inside my loop that resides inside the DAT block. I have experience programming in SPIN Language, but I am not familiar with the Assembly environment. Is there a way to possibly read the data from the global variable via. it's memory address? Is there a semantic/syntactical solution to this? Any help will be much appreciated, thank you so much!
Comments
There are a couple ways to do this.
You could make "Frequenz" a constant:
The then use this constant to define delay.
You could also just define Delay as 4000000.
Of before launching the cog, you could define Delay.
To do this, you'd need to define Delay as a long.
If you're going to hard code the value of Delay you might as well do it this way:
Yes, you can pass the address of the Frequenz variable as a parameter on cog start: Then in the Assembly code loop, you read the current value of the variable with:
... rdlong Delay,par ...par holds the address you passed in cognew's second argument. Be aware that this must be a long aligned address.Andy
If there are multiple instances of this object, there is no real solution to your problem.
If there's only a single instance then there's no reason to use the var declarations, move them to dat and it's all suddenly simple.