asm: new example

asm/asm.s

@@ -0,0 +1,73 @@
+        .section .text.start
+
+        /* vdp2 */
+
+        /* set TV Mode (see the definition of tvmd_* below) */
+        mov.l tvmd,r1
+        mov.w tvmd_v,r2
+        mov.w tvmd_r,r3
+        or r3,r2
+        mov.w r2,@r1
+
+        /* turn off all screens (make BACK visible) */
+        mov.l bgon,r1
+        mov #0,r2
+        mov.w r2,@r1
+
+        /* set the Back Screen color mode to "single color" */
+        /* set the high bits of the Back Screen Table Address to zero */
+        mov.l bktau,r1
+        mov.w bktau_v,r2
+        mov.w r2,@r1
+
+        /* set the low bits of Back Screen Table Address */
+        /* (relative to the beginning of VDP2 VRAM) */
+        mov.l bktal,r1
+        mov.w bktal_v,r2
+        mov.w r2,@r1
+
+        /* write "red" to VDP2 VRAM */
+        mov.l vram,r1
+        mov #31,r2
+        mov.w r2,@r1
+
+loop_forever:
+        bra loop_forever
+        nop
+
+        /* constants */
+
+        CACHE_THROUGH = 0x20000000
+        VDP2_BASE = 0x05E00000
+
+        VRAM = 0x000000
+
+        TVMD = 0x180000
+        TVMD__DISP = (1 << 15)
+        TVMD__BDCLMD = (1 << 8)
+        TVMD__LSMD__NON_INTERLACE = (0b00 << 6)
+        TVMD__VRESO__240 = (0b01 << 4)
+        TVMD__HRESO__NORMAL_320 = (0b000 << 0)
+
+        BGON = 0x180020
+
+
+        BKTAU = 0x1800AC
+        BKTAU__BKCLMD_SINGLE_COLOR = (0 << 15)
+
+        BKTAL = 0x1800AE
+
+        .align 4
+vram:           .long (CACHE_THROUGH | (VDP2_BASE + VRAM))
+
+tvmd:           .long (CACHE_THROUGH | (VDP2_BASE + TVMD))
+tvmd_v:         .word (TVMD__DISP | TVMD__BDCLMD | TVMD__LSMD__NON_INTERLACE)
+tvmd_r:         .word (TVMD__VRESO__240 | TVMD__HRESO__NORMAL_320)
+
+bktal:          .long (CACHE_THROUGH | (VDP2_BASE + BKTAL))
+bktal_v:        .long 32768
+
+bgon:           .long (CACHE_THROUGH | (VDP2_BASE + BGON))
+
+bktau:          .long (CACHE_THROUGH | (VDP2_BASE + BKTAU))
+bktau_v:        .word (BKTAU__BKCLMD_SINGLE_COLOR)