fox32os: Implement multitasking and add a jump table for applications

fox32os.def

@@ -0,0 +1,15 @@
+; fox32os routine definitions
+
+; system jump table
+get_os_version:   jmp [0x00000810]
+
+; FXF jump table
+parse_fxf_binary: jmp [0x00000820]
+
+; task jump table
+new_task:         jmp [0x00000830]
+yield_task:       jmp [0x00000834]
+end_current_task: jmp [0x00000838]
+
+; memory jump table
+allocate_memory:  jmp [0x00000840]

kernel/fxf/fxf.asm

@@ -4,13 +4,13 @@
 ; inputs:
 ; r0: pointer to memory buffer containing an FXF binary
 ; outputs:
-; none
-execute_fxf_binary:
+; r0: relocation address
+parse_fxf_binary:
     ; TODO: check the magic bytes and header version
 
     call fxf_reloc
 
-    jmp r0
+    ret
 
     #include "fxf/reloc.asm"
 

kernel/main.asm

@@ -9,6 +9,27 @@ const FOX32OS_VERSION_PATCH: 0
 const BACKGROUND_COLOR: 0xFF674764
 const TEXT_COLOR:       0xFFFFFFFF
 
+    jmp entry
+
+jump_table:
+    ; system jump table
+    org.pad 0x00000810
+    data.32 get_os_version
+
+    ; FXF jump table
+    org.pad 0x00000820
+    data.32 parse_fxf_binary
+
+    ; task jump table
+    org.pad 0x00000830
+    data.32 new_task
+    data.32 yield_task
+    data.32 end_current_task
+
+    ; memory jump table
+    org.pad 0x00000840
+    data.32 allocate_memory
+
     ; initialization code
 entry:
     ; clear the background
@@ -48,16 +69,23 @@ draw_startup_text:
     cmp r0, 0
     ifz jmp startup_error
 
-    ; read the startup file into memory starting at the bottom of the kernel
+    ; read the startup file into memory starting at 0x03000000
     mov r0, startup_file_struct
-    mov r1, kernel_bottom
+    mov r1, 0x03000000
     call ryfs_read_whole_file
 
-    ; relocate and execute it!!!
-    mov r0, kernel_bottom
-    call execute_fxf_binary
+    ; relocate and execute it as a new task
+    mov r0, 0x03000000
+    call parse_fxf_binary
+    mov r1, r0
+    mov r0, 0
+    mov r2, rsp
+    call new_task
 
-    rjmp 0
+    ; when the startup file yields for the first time, we'll end up back here
+    ; jump back to it without adding this "task" (not really a task) into the queue
+    ; this does not return
+    call end_current_task
 
 startup_error:
     mov r0, BACKGROUND_COLOR
@@ -74,8 +102,15 @@ startup_error:
     call draw_format_str_to_background
     rjmp 0
 
+get_os_version:
+    mov r0, FOX32OS_VERSION_MAJOR
+    mov r1, FOX32OS_VERSION_MINOR
+    mov r2, FOX32OS_VERSION_PATCH
+    ret
+
     #include "allocator.asm"
     #include "fxf/fxf.asm"
+    #include "task.asm"
 
 startup_str: data.str "fox32 - OS version %u.%u.%u" data.8 0
 startup_error_str: data.str "fox32 - OS version %u.%u.%u - startup.cfg is invalid!" data.8 0

kernel/task.asm

@@ -0,0 +1,164 @@
+; task switching routines
+
+; add a new task to the queue and jump to it immediately
+; inputs:
+; r0: task ID
+; r1: task instruction pointer
+; r2: task stack pointer
+; outputs:
+; none
+new_task:
+    bse [task_id_bitmap], r0 ; mark this task ID as used
+
+    mov r4, r2
+    mov r3, r1
+    mov r2, r0
+
+    mov r0, [task_queue_ptr]
+    call task_store
+    mov [task_queue_ptr], r0
+
+    ; fall-through
+
+; switch to the next task in the queue
+; inputs:
+; none
+; outputs:
+; none
+yield_task:
+    ; add the current task back into the queue
+    mov r0, current_task ; get the current task struct
+    call task_load
+    pop r3 ; pop the return address off of the stack
+    mov r4, rsp
+    mov r0, [task_queue_ptr]
+    call task_store
+    mov [task_queue_ptr], r0
+
+    jmp yield_task_0
+
+; switch to the next task without adding the current task back into the queue
+; inputs:
+; none
+; outputs:
+; none
+end_current_task:
+    cmp [task_queue_ptr], task_queue_bottom
+    ifz jmp task_empty
+
+    mov r0, current_task ; get the current task struct
+    call task_load
+    bcl [task_id_bitmap], r2 ; mark this task ID as unused
+    pop r0 ; pop the return address off of the stack
+yield_task_0:
+    mov r0, task_queue_bottom
+    call task_load
+    mov r0, current_task
+    call task_store
+
+    mov r1, task_queue_bottom
+yield_task_1:
+    add r1, TASK_SIZE
+
+    cmp [task_queue_ptr], r1
+    ifz jmp yield_task_2
+
+    mov r0, r1
+    call task_load
+
+    mov r0, r1
+    sub r0, TASK_SIZE
+    call task_store
+
+    jmp yield_task_1
+yield_task_2:
+    mov r0, current_task
+    call task_load
+    sub [task_queue_ptr], TASK_SIZE
+
+    mov rsp, r4
+    jmp r3
+
+; get the next unused task ID, starting at 1
+; inputs:
+; none
+; outputs:
+; r0: task ID, or zero if all IDs are used
+get_unused_task_id:
+    mov r0, 1
+get_unused_task_id_loop:
+    bts [task_id_bitmap], r0
+    ifz ret
+    inc r0
+    cmp r0, 32
+    iflt jmp get_unused_task_id_loop
+    ; if we reach this point, then add task IDs are used
+    mov r0, 0
+    ret
+
+task_load:
+    mov r2, [r0] ; task ID
+    add r0, 4
+    mov r3, [r0] ; instruction pointer
+    add r0, 4
+    mov r4, [r0] ; stack pointer
+    add r0, 4
+    ret
+
+task_store:
+    mov [r0], r2 ; task ID
+    add r0, 4
+    mov [r0], r3 ; instruction pointer
+    add r0, 4
+    mov [r0], r4 ; stack pointer
+    add r0, 4
+    ret
+
+task_empty:
+    mov r0, task_panic_str
+    mov r1, task_queue_bottom ; show the address of the task queue in the panic brk output
+    mov r2, [task_queue_ptr] ; show the the task queue pointer in the panic brk output
+    call panic
+
+task_panic_str: data.str "Task queue empty! Hanging here" data.8 10 data.8 0
+
+const TASK_SIZE: 12
+task_id_bitmap: data.32 0
+current_task:
+    data.32 0 ; task ID
+    data.32 0 ; instruction pointer
+    data.32 0 ; stack pointer
+task_queue_ptr: data.32 task_queue_bottom
+task_queue_bottom:
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0
+    data.32 0 data.32 0 data.32 0