In SX Microcontrollers, SX/B Compiler and SX-Key Tool, bean wrote:

[quote="transistortoaster"]
You used __PARAM1 in your ISR at NextTile: and PrimeTileDots:. Exactly why did you use that register? If a function is called in the main code and it gets interrupted, isn't there a problem? I know you made a subroutine to wait for the non-active video phase of the screen display, but is it necessary considering 1) that the worse case scenario is a few pixels that get updated 1/60 seconds later and 2) there are no writes to the shared memory in the ISR?
Frank,
 

  By default (unless you specify NOPRESERVE or NOCODE) SX/B saves all the __PARAMx variables at the start of the interrupt and restores them at the RETURNINT. Otherwise you would be VERY limited as to what SX/B commands you could use in an interrupt. Since many of the SX/B commands use the __PARAMx variables.

 

  All of the __PARAMx variables are really handy in assembly code because they are guarenteed (sp?) to be in the global memory area. So you can adjust FSR and still have access to them.

 

  Actually I would like to get the clock frequency down to 16x colorburst, or 57.272727MHz. The spec sheet says the SX48 cannot run above 50MHz at 3.3volts. I would like to make the color video circuit low power, so I want to run the SX at the slowest clock and lowest voltage I possibly can.

 

  I'm right now writing a Bresenham line code so I can draw lines on the screen. Fun fun fun...

 

Bean.

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