Zack Buhman
9610c428bd
This draws a nice macaw texture in a square-shaped triangle strip. The square is then rotated around the y-axis. I dealt with myriad bugs while experimenting with this, all of them entirely my fault: - macaw texture colors were incorrect because GIMP was exporting raw RGB data in gamma-corrected sRGB space, whereas the Dreamcast is in linear color space. - macaw texture colors were incorrect because I truncated color values to the least significant rather than most significant bits. - macaw rotation around the Y axis caused the macaw texture to distort, stretch and recurse in interesting and unexpected ways. This was caused by sending Z values in the wrong coordinate space (Z) contrast to what is expected by the Dreamcast (1/z). Reordering z-coordinate operations so that the reciprocal is computed last resolved this. - macaw rotation around the Y axis caused the macaw texture to warp unexpectedly, but only on real hardware. This was caused by unnecessarily negating Z coordinate values. Behavior for each of the Z-coordinate issues differed between Flycast and real Dreamcast hardware. I also did several tests related to SH4 cache behavior, particularly related to the "copy-back" mode. I verified copy-back behavior on a real dreamcast, and experimented with the operand cache write-back instruction, "ocbwb". In particular, when the `scene` buffer is access from cacheable memory, e.g: the P1 area, and CCR__CB is enabled, DMA from physical memory to the TA FIFO polygon converter will fail because the scene data has not yet been written to physical memory yet. `ocbwb` can be used to "write back" scene from the SH4 operand cache to physical memory--only the latter is visible from the CH2-DMA perspective.
31 lines
780 B
C++
31 lines
780 B
C++
#include "type.h"
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#include "sh7091.h"
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#include "sh7091_bits.h"
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#include "cache.h"
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extern volatile reg32 sh7091_ic_a[256][(1 << 5) / 4] __asm("sh7091_ic_a");
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extern volatile reg32 sh7091_oc_a[512][(1 << 5) / 4] __asm("sh7091_oc_a");
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void cache_init()
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{
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for (int i = 0; i < 256; i++) {
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sh7091_ic_a[i][0] = 0;
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}
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for (int i = 0; i < 512; i++) {
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sh7091_oc_a[i][0] = 0;
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}
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sh7091.CCN.CCR = CCR__ICI // instruction cache invalidate
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| CCR__ICE // instruction cache enable
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| CCR__OCI // operand cache invalidate
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| CCR__OCE // operand cache enable
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// | CCR__CB // enable copy-back mode for the P1 area
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;
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sh7091.CCN.MMUCR = 0;
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asm volatile ("nop;nop;nop;nop;nop;nop;nop;nop;");
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}
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