Add a frame skip setting

src/main.S

@@ -22,6 +22,8 @@
 .globl framebuffer
 .globl fps_emulate
 .globl fps_display
+.globl skip_native
+.globl skip_emulate
 .globl frame_count
 
 .globl _start
@@ -33,6 +35,8 @@ framebuffer: .word FRAMEBUFFER1
 fps_native: .byte 0
 fps_emulate: .byte 0
 fps_display: .byte 0
+skip_native: .byte 0
+skip_emulate: .byte 0
 frame_count: .byte 0
 
 .section .boot
@@ -262,6 +266,21 @@ pi_wait2:
     nop
 
 check_frame:
+    // Ignore V-blanks to match the frames being skipped
+    la k1, skipped_set
+    lbu k0, (k1)
+    srl k0, k0, 2
+    la k1, skip_native
+    lbu k1, (k1)
+    sub k0, k0, k1
+    blez k0, skip_reset
+    li k0, 0
+    addi k0, k1, 1
+skip_reset:
+    la k1, skip_native
+    bnez k0, input_update
+    sb k0, (k1)
+
     // Continue if the next frame is ready; otherwise just update input
     la k0, frame_count
     lbu k1, (k0)

src/menu.S

@@ -21,6 +21,7 @@
 
 .globl layer_set
 .globl precision_set
+.globl skipped_set
 .globl audio_set
 
 .globl update_menu
@@ -31,6 +32,7 @@
 counter_set: .byte 0 << 2
 layer_set: .byte 0 << 2
 precision_set: .byte 2 << 2
+skipped_set: .byte 0 << 2
 audio_set: .byte 1 << 2
 left_str: .string "<"
 right_str: .string ">"
@@ -40,6 +42,7 @@ title_str: .string "SODIUM64 SETTINGS"
 counter_str: .string "FPS COUNTER"
 layer_str: .string "SUB LAYER ORDER"
 precision_str: .string "FRAME PRECISION"
+skipped_str: .string "FRAMES SKIPPED"
 audio_str: .string "AUDIO OUTPUT"
 
 .align 4
@@ -53,16 +56,21 @@ medium_str: .string " MEDIUM "
 high_str: .string "   HIGH "
 higher_str: .string " HIGHER "
 max_str: .string "    MAX "
+zero_str: .string "      0 "
+one_str: .string "      1 "
+two_str: .string "      2 "
+three_str: .string "      3 "
 
 .align 4
-menu_items: .word counter_str, layer_str, precision_str, audio_str, 0
-menu_opts: .word toggle_opts, layer_opts, precision_opts, toggle_opts
-menu_sets: .word counter_set, layer_set, precision_set, audio_set
+menu_items: .word counter_str, layer_str, precision_str, skipped_str, audio_str, 0
+menu_opts: .word toggle_opts, layer_opts, precision_opts, skipped_opts, toggle_opts
+menu_sets: .word counter_set, layer_set, precision_set, skipped_set, audio_set
 
 .align 4
 toggle_opts: .word off_str, on_str, 0
 layer_opts: .word back_str, front_str, 0
 precision_opts: .word lower_str, low_str, medium_str, high_str, higher_str, max_str, 0
+skipped_opts: .word zero_str, one_str, two_str, three_str, 0
 
 .text
 .set noreorder

src/ppu.S

@@ -420,15 +420,34 @@ end_fill:
 
 .align 5
 rsp_frame:
-    // Alternate indices for queued frame values each frame
+    // Make a final frame section and get alternating queue indices
     lbu t5, queue_id // Next
+    lhu a0, cur_line
+    move t4, ra
+    jal make_section
     xori t6, t5, 4 // Current
+
+    // Skip rendering frames based on the setting
+    lbu t0, skipped_set
+    srl t0, t0, 2
+    lbu t1, skip_emulate
+    bge t1, t0, skip_reset
+    li t0, 0
+    addi t0, t1, 1
+
+skip_reset:
+    // Update the skip counter and the section pointer if not skipped
+    la t1, skip_emulate
+    bnez t0, ignore_frame
+    sb t0, (t1)
     sb t6, queue_id
+    lw t0, sect_queues(t6)
+    sw t0, section_ptr
 
     // Set initial values for palette conversion
     lbu t0, brightness
-    lw t4, pal_queues(t5)
-    addi t4, t4, 0x7F8
+    lw v1, pal_queues(t5)
+    addi v1, v1, 0x7F8
     li t6, 0x1FE
 
 update_dpal:
@@ -459,11 +478,11 @@ update_dpal:
     // Set a color in the palette queue and loop until finished
     sll t3, t2, 16
     or t2, t2, t3
-    sw t2, 0(t4)
-    sw t2, 4(t4)
+    sw t2, 0(v1)
+    sw t2, 4(v1)
     addi t6, t6, -2
     bnez t6, update_dpal
-    addi t4, t4, -8
+    addi v1, v1, -8
 
     // Copy OAM to the queue for the next frame
     la t0, oam
@@ -499,20 +518,12 @@ vram_loop:
     bne t0, t1, vram_loop
     addi t0, t0, 0x20
 
-    // Make a final frame section and reset the pointer
-    lhu a0, cur_line
-    move t4, ra
-    jal make_section
-    xori t6, t5, 4
-    lw t0, sect_queues(t6)
-    sw t0, section_ptr
-
 rsp_wait:
     // Wait until the RSP is finished rendering
     lw t0, 0xA4040010 // SP_STATUS
     andi t0, t0, 0x1 // Halt
     beqz t0, rsp_wait
-    nop
+    xori t6, t5, 0x4
 
     // Update the software-rendered UI
     lw a0, DMEM(FRAMEBUFFER)(t6)
@@ -527,7 +538,10 @@ menu_return:
     lbu t1, fps_emulate
     addi t0, t0, 1
     sb t0, frame_count
+    lbu t2, skipped_set
     addi t1, t1, 1
+    srl t2, t2, 2
+    add t1, t1, t2
     sb t1, fps_emulate
     li t0, 0x80 // Set VI mask
     sw t0, 0xA430000C // MI_MASK
@@ -572,6 +586,13 @@ frame_wait:
     jr t4
     sw t0, 0x0010(t1) // SP_STATUS
 
+ignore_frame:
+    // Reset the section pointer and reuse it for the next frame
+    lw t0, sect_queues(t5)
+    sw t0, section_ptr
+    jr t4
+    nop
+
 .align 5
 vram_trans8: // t0: address, t6: return - t1: output
     // Perform 8-bit translation on a VRAM address