Add Propeller firmware and assembly example for bitmap mode

Author: fjmilens3

Spin/cody_line.spin

@@ -181,6 +181,10 @@ if_z            mov     buffer_ptr, buffer2_ptr
 ' line is fetched. Finally the character is blitted to the scanline buffer
 ' using the current colors. (Adjustments are made for soft-scrolling when
 ' scrolling is enabled.)
+' 
+' In bitmap mode the layout is slightly different. Data is read as in
+' character mode, but the screen memory is arranged as a sequence of 1000
+' multicolor "characters" instead. The actual character memory is unused.
 '
 render_chars            
                 ' Set up the output pointer taking into account the left "margin" for sprites
@@ -210,18 +214,22 @@ if_nz           mov     adjustv, scrollv
                 nop
 
 :load_offset    mov     screen_memory_offset, 0_0
-
-                ' Calculate the locations in screen and color memory using the offset above
-                mov     curr_screen_ptr, scrmem_ptr
-                add     curr_screen_ptr, screen_memory_offset
 
+                ' Calculate the locations in color and screen memory using the offset above
                 mov     curr_colors_ptr, colmem_ptr
                 add     curr_colors_ptr, screen_memory_offset
-                                        
+                
+                test    controlreg, #%00010000 wz
+if_z            mov     curr_screen_adv, #1
+if_nz           mov     curr_screen_adv, #8
+if_nz           shl     screen_memory_offset, #3
+                
+                mov     curr_screen_ptr, scrmem_ptr
+                add     curr_screen_ptr, screen_memory_offset
+                
                 mov     chars_remaining, #40
 
-:char_loop      
-                rdbyte  color_data, curr_colors_ptr
+:char_loop      rdbyte  color_data, curr_colors_ptr
 
                 shl     color_data, #1
                 add     color_data, lookup_ptr
@@ -231,19 +239,18 @@ if_nz           mov     adjustv, scrollv
 
                 add     curr_colors_ptr, #1
 
-                rdbyte  source_ptr, curr_screen_ptr
-                shl     source_ptr, #3
-                add     source_ptr, chrset_ptr
+                test    controlreg, #%00010000              wz
+if_nz           mov     source_ptr, curr_screen_ptr
+if_z            rdbyte  source_ptr, curr_screen_ptr
+if_z            shl     source_ptr, #3
+if_z            add     source_ptr, chrset_ptr
                 add     source_ptr, char_offset_y
-                
-                rdbyte  pixel_data, source_ptr
-                
                 add     dest_ptr, #3
+                rdbyte  pixel_data, source_ptr
 
                 mov     pixels_remaining, #4
 
-:pixel_loop     
-                mov     temp, pixel_data
+:pixel_loop     mov     temp, pixel_data
                 and     temp, #%11
 
                 shl     temp, #3
@@ -258,7 +265,7 @@ if_nz           mov     adjustv, scrollv
                 djnz    pixels_remaining, #:pixel_loop
 
                 add     dest_ptr, #5
-                add     curr_screen_ptr, #1
+                add     curr_screen_ptr, curr_screen_adv
 
                 djnz    chars_remaining, #:char_loop                        
 
@@ -598,6 +605,7 @@ temp                    long    $0
 curr_chrset_ptr         long    0
 curr_screen_ptr         long    0
 curr_colors_ptr         long    0
+curr_screen_adv         long    0
 
 TOGGLE_EMPTY            long    $0
 TOGGLE_FRAME            long    $1

Spin/cody_video.spin

@@ -65,7 +65,7 @@
 ' Bit 1 - If set, enables vertical scrolling (and reduces screen height by one row)
 ' Bit 2 - If set, enables horizontal scrolling (and reduces screen width by two cols)
 ' Bit 3 - If set, enables row effects.
-' Bit 4 - Unused.
+' Bit 4 - If set, enables bitmap mode.
 ' Bit 5 - Unused.
 ' Bit 6 - Unused.
 ' Bit 7 - Unused.

Tass/Makefile

@@ -1,4 +1,4 @@
-all: codybasic.bin codybros.bin codycart.bin codyprog.bin codysid.bin
+all: codybasic.bin codybros.bin codycart.bin codyprog.bin codysid.bin codybitmap.bin
 
 %.bin: %.asm
 	64tass --mw65c02 --nostart -o $@ $<