nullbios: implement fix_clear and lsp_1st BIOS calls

Author: dciabrin

nullbios/biosstart.S

@@ -115,9 +115,9 @@ _unused_jmptable_slots:
         jmp	bios_noop.l
         .endr
 bios_fix_clear:
-        jmp     not_implemented.l
+        jmp     impl_fix_clear.l
 bios_lsp_1st:
-        jmp     not_implemented.l
+        jmp     impl_lsp_1st.l
 bios_mess_out:
         jmp     not_implemented.l
 bios_controller_setup:

nullbios/gfx.c

@@ -0,0 +1,99 @@
+/*
+ * controllers management for BIOS
+ * Copyright (c) 2025 Damien Ciabrini
+ * This file is part of ngdevkit
+ *
+ * ngdevkit is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * ngdevkit is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with ngdevkit.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <ngdevkit/bios-backup-ram.h>
+#include <ngdevkit/registers.h>
+#include "utils.h"
+
+// Note: when gcc determines that a variable holds a constant rvalues,
+// it skips register assignment and generate instructions with
+// immediate addressing mode instead, which can be suboptimal.
+//
+// In the functions below, we use asm block to assign variables for
+// which gcc must not perform constant optimizations. This yields
+// better performance:
+//   - peephole generates faster loops that use the "dbra" opcode
+//   - the memory writes in the loop have a smaller code size
+
+// BIOS public API
+
+#define OPAQUE_TILE      0x20
+#define TRANSPARENT_TILE 0xff
+
+void impl_fix_clear() {
+    s16 loop;
+    u16 tile;
+
+    volatile u16 *vram;
+    // VRAM access: beginning of tile map, 1 byte per write (next tile down)
+    *REG_VRAMADDR = ADDR_FIXMAP;
+    *REG_VRAMMOD = 1;
+    SET_CONST_ADDR(vram, REG_VRAMRW);
+
+    // left column
+    SET_CONST_W(loop, 32-1);
+    SET_CONST_W(tile, OPAQUE_TILE);
+    do { *vram = tile; } while(--loop != -1);
+    // full center tilemap
+    SET_CONST_W(loop, 32*38-1);
+    SET_CONST_W(tile, TRANSPARENT_TILE);
+    do { *vram = tile; } while(--loop != -1);
+    // right column
+    SET_CONST_W(loop, 32-1);
+    SET_CONST_W(tile, OPAQUE_TILE);
+    do { *vram = tile; } while(--loop != -1);
+}
+
+
+#define SCB2_VAL(zx, zy) (((zx)<<8) | (zy))
+#define SCB3_VAL(y, sticky, size) ((((y))<<7) | ((sticky)<<6) | (size))
+#define SCB4_VAL(x) ((x)<<7)
+
+void impl_lsp_1st() {
+    s16 loop;
+    u16 val;
+
+    volatile u16 *vram;
+    // VRAM access: sprite attributes, 1 byte per write (to next sprite)
+    *REG_VRAMADDR = ADDR_SCB2;
+    *REG_VRAMMOD = 1;
+    SET_CONST_ADDR(vram, REG_VRAMRW);
+
+    // current VRAM pointer: SCB2
+    // reset shrink coefficient: max x (0xf) | max y (0xff)
+    SET_CONST_W(loop, 512-1);
+    SET_CONST_W(val, SCB2_VAL(0xf, 0xff));
+    do { *vram = val; } while(--loop != -1);
+    // current VRAM pointer: SCB3
+    // reset vertical position: topmost (0)
+    SET_CONST_W(loop, 512-1);
+    SET_CONST_W(val, SCB3_VAL(0, 0, 0));
+    do { *vram = val; } while(--loop != -1);
+    // current VRAM pointer: SCB4
+    // reset horizontal position: leftmost (0)
+    SET_CONST_W(loop, 512-1);
+    SET_CONST_W(val, SCB4_VAL(380));
+    do { *vram = val; } while(--loop != -1);
+    // special case: configure all tiles of 1st sprite to be transparent
+    *REG_VRAMADDR = ADDR_SCB1;
+    *REG_VRAMMOD = 2;
+    SET_CONST_W(loop, 32-1);
+    SET_CONST_W(val, TRANSPARENT_TILE);
+    do { *vram = val; } while(--loop != -1);
+}

nullbios/utils.h

@@ -44,4 +44,10 @@
              : "d" ((y))     \
              : "cc")
 
+#define SET_CONST_W(var, cst) \
+__asm__ ("move.w %1, %0" : "=r" (var) : "i" (cst) :);
+
+#define SET_CONST_ADDR(var, cst) \
+__asm__ ("movea.l %1, %0" : "=r" (var) : "i" (cst) :);
+
 #endif /* __NULLBIOS_UTILS_H__ */