From 4301bbd4b789c26ca663c3424704826960e6e4cf Mon Sep 17 00:00:00 2001
From: Zack Buhman <zack@buhman.org>
Date: Fri, 8 Aug 2025 15:21:24 -0500
Subject: [PATCH] vdp2: incomplete rbg0 example

---
 Makefile           |   4 +-
 vdp2/rbg0_font.cpp | 106 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 109 insertions(+), 1 deletion(-)
 create mode 100644 vdp2/rbg0_font.cpp

diff --git a/Makefile b/Makefile
index 8654775..7a49a55 100644
--- a/Makefile
+++ b/Makefile
@@ -55,7 +55,9 @@ vdp2/nbg0.elf: vdp2/nbg0.o res/butterfly.data.o res/butterfly.data.pal.o
 
 vdp2/nbg0_16color.elf: vdp2/nbg0_16color.o res/kirby.data.o res/kirby.data.pal.o
 
-vdp2/nbg0_font.elf: vdp2/nbg0_font.o font/hp_100lx_4bit.data.o
+vdp2/nbg0_font.elf: vdp2/nbg0_font.o saturn/start.o font/hp_100lx_4bit.data.o
+
+vdp2/rbg0_font.elf: vdp2/rbg0_font.o saturn/start.o font/hp_100lx_4bit.data.o
 
 vdp2/color_calculation_ratio.elf: vdp2/color_calculation_ratio.o res/mai00.data.o res/mai.data.pal.o res/haohmaru.data.o res/haohmaru.data.pal.o res/forest.data.pal.o res/forest.pattern.o res/forest.tile.o
 
diff --git a/vdp2/rbg0_font.cpp b/vdp2/rbg0_font.cpp
new file mode 100644
index 0000000..d542f71
--- /dev/null
+++ b/vdp2/rbg0_font.cpp
@@ -0,0 +1,106 @@
+#include <stdint.h>
+
+#include "vdp2.h"
+#include "../common/vdp2_func.hpp"
+
+#include "font/hp_100lx_4bit.data.h"
+
+void cell_data()
+{
+  const uint32_t * start = reinterpret_cast<uint32_t *>(&_binary_font_hp_100lx_4bit_data_start);
+  const int size = reinterpret_cast<uint32_t>(&_binary_font_hp_100lx_4bit_data_size);
+
+  // the start of VRAM-A0
+  for (int i = 0; i < (size / 4); i++) {
+    vdp2.vram.u32[i] = start[i];
+  }
+}
+
+void palette_data()
+{
+  vdp2.cram.u16[0] = 0x0000;
+  vdp2.cram.u16[1] = 0xffff;
+}
+
+void main()
+{
+  v_blank_in();
+
+  // 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);
+
+  /* set the color mode to 5bits per channel, 1024 colors */
+  vdp2.reg.RAMCTL = RAMCTL__CRMD__RGB_5BIT_1024
+                  | RAMCTL__VRAMD
+                  | RAMCTL__VRBMD
+                  | RAMCTL__RDBSA0__CHARACTER_PATTERN_TABLE // VRAM-A0 0x000000
+                  | RAMCTL__RDBSA1__PATTERN_NAME_TABLE;     // VRAM-A1 0x020000
+
+  vdp2.reg.VRSIZE = 0;
+
+  /* enable display of NBG0 */
+  vdp2.reg.BGON = BGON__R0ON | BGON__R0TPON;
+
+  /* set character format for NBG0 to palettized 16 color
+     set enable "cell format" for NBG0
+     set character size for NBG0 to 1x1 cell */
+  vdp2.reg.CHCTLB = CHCTLB__R0CHCN__16_COLOR
+                  | CHCTLB__R0BMEN__CELL_FORMAT
+                  | CHCTLB__R0CHSZ__1x1_CELL;
+
+  /* plane size */
+  vdp2.reg.PLSZ = PLSZ__RAPLSZ__1x1
+                | PLSZ__RBPLSZ__1x1;
+
+  /* map plane offset
+     1-word: value of bit 6-0 * 0x2000
+     2-word: value of bit 5-0 * 0x4000
+  */
+  // plane_a_offset is at the start of VRAM-A1
+  constexpr int plane_a = 8;
+  constexpr int plane_a_offset = plane_a * 0x4000;
+
+  constexpr int page_size = 64 * 64 * 2; // N0PNB__1WORD (16-bit)
+  constexpr int plane_size = page_size * 1;
+
+  /* cycle pattern table not used for RBG0 ? */
+  vdp2.reg.CYCA0 = 0x0F44F99F;
+  vdp2.reg.CYCA1 = 0x0F44F99F;
+  vdp2.reg.CYCB0 = 0x0F44F99F;
+  vdp2.reg.CYCB1 = 0x0F44F99F;
+
+  vdp2.reg.MPOFR = MPOFR__RAMP(0); // bits 8~6
+  vdp2.reg.MPABRA = MPABRA__RAMPB(plane_a) | MPABRA__RAMPA(plane_a); // bits 5~0
+  vdp2.reg.MPCDRA = MPCDRA__RAMPD(plane_a) | MPCDRA__RAMPC(plane_a); // bits 5~0
+
+  vdp2.reg.PNCR = PNCR__R0PNB__2WORD;
+
+  vdp2.reg.RPMD = RPMD__ROTATION_PARAMETER_A;
+
+  vdp2.reg.RPRCTL = 0;
+
+  vdp2.reg.KTCTL = 0;
+
+  vdp2.reg.KTAOF = 0;
+
+  vdp2.reg.RPTA = 0;
+
+  /* */
+
+  palette_data();
+  cell_data();
+
+  for (int i = 0; i < 64 * 64; i++) {
+    vdp2.vram.u32[(plane_a_offset / 4) + i] = ' ' - 0x20;
+  }
+
+  const char * test = "If sound level changes progressively, volume on 3 bit makes audi";
+  int ix = 0;
+  while (*test) {
+    uint8_t c = *test++;
+    vdp2.vram.u32[(plane_a_offset / 4) + ix++] = c - 0x20;
+  }
+
+  while (1);
+}