thejpster
commented
3 months ago Although on the RP2040, it's not quite fast enough to keep up and the display flickers. The hot loop looks like this:
// Write eight pixels (32-bits) to interpolator Lane 0
str r3, [r6, #0]
// Write eight pixels (32-bits) to interpolator Lane 1
str r3, [r6, #4]
// Read palette address from Lane 0
ldr r4, [r0, #0]
// Read palette address from Lane 1
ldr r5, [r0, #4]
// Load 16-bit palette entry for left pixel
ldrh r4, [r4, #0]
// Load 16-bit palette entry for right pixel
ldrh r5, [r5, #0]
// Mix two pixels together
lsls r5, r5, #16
adds r4, r5, r4
// Write 32-bit pixel pair to scanline buffer
str r4, [r1, #0]
The interpolator was pulling out the wrong palette values - but now it's fixed.