Question about hubexec code alignment

Comments

• RossH Posts: 5,345

  2022-12-17 10:32

  @"Christof Eb." said:

  Is it true, that it is not necessary to have code long-alinged for hubexec? Codes can start at any byte?

  This is true. But the timing is affected.
• Christof Eb. Posts: 1,103

  2022-12-17 11:16 edited 2022-12-17 11:55

  Thank you very much!
• TonyB_ Posts: 2,125

  2022-12-17 11:46

  @RossH said:

  @"Christof Eb." said:

  Is it true, that it is not necessary to have code long-alinged for hubexec? Codes can start at any byte?

  This is true. But the timing is affected.

  Misalignment has small effect on timing, minimal really. FIFO reloading and hub word or long accesses take one more cycle but instructions take same time as cog / LUT exec if they don't involve hub RAM.
• evanh Posts: 15,187

  2022-12-17 13:13

  CALLD is one instruction to be very careful with how it gets used. It relies on those registers for remembering the return address at a later place in time and code. They can be used in neat ways, eg: the interrupt ISRs are called via a wired version of that instruction.

  But write that register in the interim and you've got an imminent crash on your hands. The "switch back from assembler code" will rely on a prior setup of PTRA which cannot be altered by the remainder of the assembly code itself.
• Rayman Posts: 13,860

  2022-12-18 16:41

  @TonyB_ said:

  Misalignment has small effect on timing, minimal really. FIFO reloading and hub word or long accesses take one more cycle but instructions take same time as cog / LUT exec if they don't involve hub RAM.

  I must have forgotten about that…
  Guess that means FlexProp hubexec code could be slightly slower for loops and jumps if not long aligned. It probably is long aligned though, I’m assuming…