vdp1: add color bank example

Makefile

@@ -30,6 +30,8 @@ vdp2/nbg0.elf: vdp2/nbg0.o res/butterfly.data.o res/butterfly.data.pal.o
 vdp1/polygon.elf: vdp1/polygon.o
 vdp1/normal_sprite.elf: vdp1/normal_sprite.o res/mai00.data.o res/mai.data.pal.o
 
+vdp1/normal_sprite_color_bank.elf: vdp1/normal_sprite_color_bank.o res/mai00.data.o res/mai.data.pal.o
+
 res/mai.data: res/mai00.data res/mai01.data res/mai02.data res/mai03.data res/mai04.data res/mai05.data res/mai06.data res/mai07.data res/mai08.data res/mai09.data res/mai10.data res/mai11.data res/mai12.data res/mai13.data res/mai14.data res/mai15.data
 	cat $(sort $^) > $@
 

vdp1/normal_sprite_color_bank.cpp

@@ -0,0 +1,155 @@
+#include <stdint.h>
+#include "vdp2.h"
+#include "vdp1.h"
+
+extern void * _mai_data_pal_start __asm("_binary_res_mai_data_pal_start");
+extern void * _mai_data_pal_size __asm("_binary_res_mai_data_pal_size");
+
+extern void * _mai00_data_start __asm("_binary_res_mai00_data_start");
+extern void * _mai00_data_size __asm("_binary_res_mai00_data_size");
+
+inline constexpr uint16_t rgb15(const uint8_t * rgb24)
+{
+  return ((rgb24[2] >> 3) << 10) // blue
+       | ((rgb24[1] >> 3) << 5)  // green
+       | ((rgb24[0] >> 3) << 0); // red
+}
+
+void color_palette(uint32_t color_bank)
+{
+  const uint32_t buf_size = reinterpret_cast<uint32_t>(&_mai_data_pal_size);
+  if (buf_size != (0x20 * 3 / 2)) while (1); // halt if buf_size is incorrect
+
+  const uint8_t * buf = reinterpret_cast<uint8_t*>(&_mai_data_pal_start);
+
+  uint16_t * table = &vdp2.cram.u16[256 * color_bank];
+
+  uint32_t buf_ix = 0;
+  for (uint32_t i = 0; i < (buf_size / 3); i++) {
+    // there is a typo in "5.2 Color Lookup Tables" "If RGB code, MSB = 0"
+    // should be "MSB = 1". The "MSB = 0" claim is correctly contradicted later.
+
+    table[i] = rgb15(&buf[buf_ix]);
+    // _mai_data_pal is rgb24, 3 bytes per color
+    buf_ix += 3;
+  }
+}
+
+uint32_t character_pattern_table(const uint32_t top)
+{
+  const uint32_t buf_size = reinterpret_cast<uint32_t>(&_mai00_data_size);
+  const uint16_t * buf = reinterpret_cast<uint16_t*>(&_mai00_data_start);
+
+  // Unlike vdp2 cell format, vdp1 sprites appear to be much more dimensionally
+  // flexible. The data is interpreted as a row-major packed array, where the
+  // row/horizontal stride is equal to the sprite width (as configured in the
+  // draw command). This is identical to how the input palette index data is
+  // structured, so there is no transformation to do here, only a plain memory
+  // copy.
+
+  // Multiply `buf_size` by one because this converts (indexed color) 8 bit pixels
+  // to 8 bit pixels. Round up to the nearest 0x20 (for an 8000 pixel/8000 byte
+  // image, this rounding is a no-op).
+  const uint32_t table_size = ((buf_size * 1) + 0x20 - 1) & (-0x20);
+  const uint32_t table_address = top - table_size;
+  uint16_t * table = &vdp1.vram.u16[(table_address / 2)];
+
+  // `table_size` is in bytes; divide by two to get uint16_t indicies.
+  uint32_t buf_ix = 0;
+  for (uint32_t table_ix = 0; table_ix < (table_size / 2); table_ix++) {
+    uint32_t tmp = buf[buf_ix];
+
+    table[table_ix] = (((tmp >> 8) & 0xff) << 8)
+                    | (((tmp >> 0) & 0xff) << 0);
+
+    buf_ix += 1;
+  }
+
+  return table_address;
+}
+
+void main()
+{
+  uint32_t color_address, character_address;
+  uint32_t top = (sizeof (union vdp1_vram));
+  uint32_t color_bank = 5; // completely random and arbitrary value
+  color_palette(color_bank);
+  // For color bank color, COLR is concatenated bitwise with pixel data. See
+  // Figure 6.17 in the VDP1 manual.
+  color_address = color_bank << 8;
+  top = character_address = character_pattern_table(top);
+
+  // DISP: Please make sure to change this bit from 0 to 1 during V blank.
+  vdp2.reg.TVMD = ( TVMD__DISP | TVMD__LSMD__NON_INTERLACE
+                  | TVMD__VRESO__240 | TVMD__HRESO__NORMAL_320);
+
+  // VDP2 User's Manual:
+  // "When sprite data is in an RGB format, sprite register 0 is selected"
+  // "When the value of a priority number is 0h, it is read as transparent"
+  //
+  // From a VDP2 perspective: in VDP1 16-color lookup table mode, VDP1 is still
+  // sending RGB data to VDP2. This sprite color data as configured in
+  // `color_lookup_table` from a VDP2 priority perspective uses sprite register 0.
+  //
+  // The power-on value of PRISA is zero. Set the priority for sprite register 0
+  // to some number greater than zero, so that the color data is not interpreted
+  // as "transparent".
+  vdp2.reg.PRISA = PRISA__S0PRIN(1); // Sprite register 0 PRIority Number
+
+  /* TVM settings must be performed from the second H-blank IN interrupt after the
+  V-blank IN interrupt to the H-blank IN interrupt immediately after the V-blank
+  OUT interrupt. */
+  // "normal" display resolution, 16 bits per pixel, 512x256 framebuffer
+  vdp1.reg.TVMR = TVMR__TVM__NORMAL;
+
+  // swap framebuffers every 1 cycle; non-interlace
+  vdp1.reg.FBCR = 0;
+
+  // during a framebuffer erase cycle, write the color "black" to each pixel
+  constexpr uint16_t black = 0x0000;
+  vdp1.reg.EWDR = black;
+
+  // the EWLR/EWRR macros use somewhat nontrivial math for the X coordinates
+  // erase upper-left coordinate
+  vdp1.reg.EWLR = EWLR__16BPP_X1(0) | EWLR__Y1(0);
+
+  // erase lower-right coordinate
+  vdp1.reg.EWRR = EWRR__16BPP_X3(319) | EWRR__Y3(239);
+
+  vdp1.vram.cmd[0].CTRL = CTRL__JP__JUMP_NEXT | CTRL__COMM__SYSTEM_CLIP_COORDINATES;
+  vdp1.vram.cmd[0].LINK = 0;
+  vdp1.vram.cmd[0].XC = 319;
+  vdp1.vram.cmd[0].YC = 239;
+
+  vdp1.vram.cmd[1].CTRL = CTRL__JP__JUMP_NEXT | CTRL__COMM__LOCAL_COORDINATE;
+  vdp1.vram.cmd[1].LINK = 0;
+  vdp1.vram.cmd[1].XA = 0;
+  vdp1.vram.cmd[1].YA = 0;
+
+  vdp1.vram.cmd[2].CTRL = CTRL__JP__JUMP_NEXT | CTRL__COMM__NORMAL_SPRITE;
+  vdp1.vram.cmd[2].LINK = 0;
+  // The "end code" is 0xf, which is being used in the mai sprite palette. If
+  // both transparency and end codes are enabled, it seems there are only 14
+  // usable colors in the 4-bit color mode.
+  vdp1.vram.cmd[2].PMOD = PMOD__ECD | PMOD__COLOR_MODE__COLOR_BANK_256;
+  // It appears Kronos does not correctly calculate the color address in the
+  // VDP1 debugger. Kronos will report FFFC when the actual color table address
+  // in this example is 7FFE0.
+  vdp1.vram.cmd[2].COLR = color_address; // non-palettized (rgb15) color data
+  vdp1.vram.cmd[2].SRCA = character_address >> 3;
+  vdp1.vram.cmd[2].SIZE = SIZE__X(72) | SIZE__Y(100);
+  vdp1.vram.cmd[2].XA = 100;
+  vdp1.vram.cmd[2].YA = 100;
+
+  vdp1.vram.cmd[3].CTRL = CTRL__END;
+
+  // start drawing (execute the command list) on every frame
+  vdp1.reg.PTMR = PTMR__PTM__FRAME_CHANGE;
+}
+
+extern "C"
+void start(void)
+{
+  main();
+  while (1) {}
+}