[peterfirefly]

If you want to fill values into memory, use PUSH xx instructions. Just move the SP to right position and starting pushing. It's faster than LDIR.

[Dwedit]

Just make sure you don't mind the interrupts also writing to that memory...

[becurious]

It’s a Spectrum. You’re going to do a HALT to sync with the start of the frame and then cycle count to prevent tearing. You can disable interrupts if you know how long you have to render your frame before the beam catches you (or let it pass then start rendering).