[stusmith1977]

Reminds me fondly of the time I was writing assembler for the ARM2/3... it had such a nice instruction set that made hand-writing assembler pleasant.

It had a "barrel shifter" that gave you free shifts of powers of two, so you could calculate screen byte offsets quickly:

  // offset = x + y * 320
  ADD R0, R1, R2, LSL #8
  ADD R0, R0, R2, LSL #5
  // = 2 cycles

It also had bulk loads and stores that made reading/writing RAM cheaper. The trick there was to spill as many registers as you possibly could, so that you could transfer as many words as possible per bulk load/store.

  LDMIA R10!, {R0-R9}
  STMIA R11!, {R0-R9}
  // Transfers 40 bytes from memory pointed to by R10 to memory pointed to by R11,
  // And updates both pointers to the new addresses,
  // And only takes (3+10)*2 = 26 cycles to do the lot.

Happy days...

[Sheepshow]

Here's how that would look in the instruction set we use here ($100M commercial product)

    ; ARM spells it
    ADD R0, R1, R2, LSL #8
    
    ; We spell it
    CLX R0           ; 1 cycles
    ADX R1           ; 1 
    ADX R2           ; 1
    LDX N, 8         ; 3
    RSX              ; N (const 8 in this case)

Try optimizing THAT!

[dmm]

If you ever feel like reliving a bit of your past the Game Boy Advance uses the ARMv3 instruction set. With an easily available flash cart you have a cool little portable system to develop on.

[eropple]

Nit: the GBA uses an ARM7TDMI that IIRC implements ARMv4T, which isn't a strict superset of ARMv3 (I think that's the first ARM that dropped the old crazy addressing). Still very fun to mess with.

[dmm]

Sorry about that! The ARM naming scheme confuses the hell out of me. I always mix up the processor generations and instruction sets.

[mattbee]

ARM was my start with assembler too. But you appear to a have forgotten there are 5 more registers you can use for that blit ;-)

[stusmith1977]

I can't remember how tight I made it... but I would think you need a couple spare: one for the number of iterations, and another for the screen stride. But yes, spilling registers like SP and LR is a useful trick if you need it.