PASM variables using RES

Comments

• Rayman Posts: 15,390

  2009-05-13 19:14 edited 2009-05-13 19:14

  Good question. I would guess that it wouldn't be random, but the actual value of HUB ram that follows the cog code...
  
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• ericball Posts: 774

  2009-05-13 19:17 edited 2009-05-13 19:17

  Rayman said...
  Good question. I would guess that it wouldn't be random, but the actual value of HUB ram that follows the cog code...
  
  

  Your guess would be correct.· RES variables must be considered uninitialized.· If you want it to be zero on load you must declare it as LONG 0.
  
  
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• Phil Pilgrim (PhiPi) Posts: 23,514

  2009-05-13 20:05 edited 2009-05-13 20:05

  Assuming you follow the rules and put your RES variables last, they will be initialized to whatever is in hub RAM after the last BYTE, WORD, or LONG in your DAT section. In other words, RES variables take up no space of their own in hub RAM but overlap with whatever follows the defined stuff. When the cog loads, that overlapping data gets loaded with it, up to the 496-long limit.
  
  -Phil
• JonnyMac Posts: 9,386

  2009-05-13 20:05 edited 2009-05-13 20:05

  Thanks for the feedback; I used mov phase, #0 in the setup section of the code -- everything is fine.
• MagIO2 Posts: 2,243

  2009-05-13 21:57 edited 2009-05-13 21:57

  If you have to move a value to the a variable which is defined by RES there is no difference in memory usage. Then you could also use long to define it, because the mov itself also needs 32 bits. So, I prefer the definition via LONG because you can initialize it with any value. If you initialize a RES with a mov, then you can only assign values in a range from $000 to $1FF.
• Phil Pilgrim (PhiPi) Posts: 23,514

  2009-05-13 22:01 edited 2009-05-13 22:01

  MagIO2 said...
  If you have to move a value to the a variable which is defined by RES there is no difference in memory usage.

  That depends on how many times you have to do it. If but once at the beginning, you're right. But if it's a loop counter, for example, that has to be reinitialized each time at the beginning of the loop, a RES will save hub space.
  
  -Phil