Subversion Repositories openrisc_2011-10-31

/* start.S -- bootup code for the Bender board using the Or1k
 *            architecture.
 *      
 *  Copyright (C) 2001 Chris Ziomkowski, chris@asics.ws
 *
 *  This file is distributed as part of the RTEMS package from
 *  OAR Corporation, and follows the licensing and distribution
 *  terms as stated for RTEMS. 
 *
 *  COPYRIGHT (c) 1989-1999.
 *  On-Line Applications Research Corporation (OAR).
 *  Copyright assigned to U.S. Government, 1994.
 *
 *  The license and distribution terms for this file may be
 *  found in the file LICENSE in this distribution or at
 *  http://www.OARcorp.com/rtems/license.html.
 */
        
#include "asm.h"


/* Since we don't yet have a memory map for Bender, I am
   assuming the following. Hopefully, this will be easily
   modified once we get the real values.

   0x00000000 - 0x00200000:    Flash/ROM (boot code / 2 MB)
   0x01000000 - 0x010FFFFF:    Synchronous SRAM (area 2 / 1 MB)
   0x10000000 - 0x1FFFFFFF:    External SDRAM (area 3 / 256 MB)
   0x20000000 - 0x2FFFFFFF:    External SDRAM (area 4 / 256 MB)

   0x80000000 - 0x8000001F:    4 16550 UART controllers
   0x80010000 - 0x80017FFF:    Internal Bender RAM
   0x80020000 - 0xFFFFFFFF:    Memory mapped Bender Peripherals

   For this version, I assume that only the flash and 32 MB
   of RAM in area 3 are populated. Everything else should
   return a bus error when accessed.
*/
.file   "start.S"
        
.data
        PUBLIC(Or1k_Interrupt_Vectors)
SYM (Or1k_Interrupt_Vectors):   
        .word   0x00000000                      # No Vector
        .word   _start                          # Reset Vector (Ignored)
        .word   __Internal_error_Occurred       # Bus Error
        .word   __Internal_error_Occurred       # Data Page Fault
        .word   __Internal_error_Occurred       # Instruction Page Fault
        .word   __int_reenable                  # Low Priority Interrupt
        .word   __Internal_error_Occurred       # Alignment Exception
        .word   __Internal_error_Occurred       # Illegal Instruction Exception
        .word   __int_reenable                  # High Priority Interrupt
        .word   __Internal_error_Occurred       # ITBL Miss
        .word   __Internal_error_Occurred       # DTBL Miss
        .word   0x00000000                      # Range Exception
        .word   0x00000000                      # System Call
        .word   0x00000000                      # Breakpoint
        .word   0x00000000                      # Trap

/*
        PUBLIC(BOTTOM_OF_MEMORY)
SYM (BOTTOM_OF_MEMORY): 
        .word   0x10000000       # Assume RAM @ 0 for the sim

        PUBLIC(TOP_OF_MEMORY)
SYM (TOP_OF_MEMORY):    
        .word   0x10800000      # Assume RAM @ 0 for the sim
*/      
        PUBLIC(_mem_end)
SYM (_mem_end):
        .word   0x10800000
        
        BEGIN_CODE
        .org    0x0
        /**************/
        /*   _panic   */
        /**************/

        /* Place the panic vector at 0 */
        
.proc   __panic
        .def    __panic
        .val    __panic
        .scl    2
        .type   044
        .endef
        .global __panic
__panic:
        
        l.jal           __exit
        l.nop
        
.endproc __panic
        .def    __panic
        .val    .
        .scl    -1
        .endef

        /* Exception processing...first, we will save the
           16 non callee saved registers which could be
           corrupted by calling a C function. We have no
           way of knowing which of these will be used, so
           we have to save all of them. We will then save
           the EPCR and ESR, in case a nested exception is
           called. Next, we call the user function. We then
           restore all the registers to their original
           values, and finally disable exceptions, restore
           EPCR and ESR (EEAR is not essential to restore)
           and then return from the interrupt. */
           
        /******************************************/
        /*       Normal exception handling        */
        /* Called with 80 bytes allocated on the  */
        /* stack, the vector function in r11, and */
        /* the vector number in r3. Original      */
        /* values at 28(r1) and 0(r1).            */
        /******************************************/
.proc   ___standard_exception
        .def    ___standard_exception
        .val    ___standard_exception
        .scl    2
        .type   044
        .endef
        .global ___standard_exception
___standard_exception:          
        l.sfeqi r11,0                   /* Ignore it if it is zero */
        l.bf    L2_2
        l.sw    4(r1),r4                /* Save r4 */

        /* Ignore fast context switching in this release. */
        /* It's poorly conceived, and will probably never */
        /* be implemented...                              */

        l.sw    8(r1),r5
        l.sw    12(r1),r6
        l.sw    16(r1),r7
        
        l.mfspr r4,r0,0x20              /* Save EPCR */
        l.mfspr r5,r0,0x30              /* Save EEAR */
        l.mfspr r6,r0,0x40              /* Save ESR */
        
        l.mfspr r7,r0,17
        l.ori   r7,r7,2
        l.mtspr r0,r7,17                /* Reenable exceptions */

        l.sw    20(r1),r8
        l.sw    24(r1),r9
        l.sw    32(r1),r12
        l.sw    36(r1),r14
        l.sw    40(r1),r16
        l.sw    44(r1),r18
        l.sw    48(r1),r20
        l.sw    52(r1),r22
        l.sw    56(r1),r24
        l.sw    60(r1),r26
        l.sw    64(r1),r28
        l.sw    68(r1),r30
        l.sw    72(r1),r4               /* Save EPCR. User could change r4 */

        /* Now, call the installed handler with the arguments:
                r3 ==> vector # (1-14)
                r4 ==> EPCR
                r5 ==> EEAR
                r6 ==> ESR
                r11 ==> User function
        */

        l.jal   ___user_function        /* Call the user routine */
        l.sw    76(r1),r6               /* Save ESR. User could change r6 */
                                        /* Ignore r5 (EEAR). It is not critical for state */

        l.lwz   r30,68(r1)
        l.lwz   r28,64(r1)
        l.lwz   r26,60(r1)
        l.lwz   r24,56(r1)
        l.lwz   r22,52(r1)
        l.lwz   r20,48(r1)
        l.lwz   r18,44(r1)
        l.lwz   r16,40(r1)
        l.lwz   r14,36(r1)
        l.lwz   r12,32(r1)
        l.lwz   r9,24(r1)
        l.lwz   r8,20(r1)
        l.lwz   r7,16(r1)
        l.lwz   r5,8(r1)

        l.addi  r6,r0,-3                /* Set r6 to 0xFFFFFFFD */
        l.mfspr r3,r0,17                /* Get SR value */
        l.and   r3,r3,r6                /* Clear exception bit */
        l.mfspr r0,r3,17                /* Disable exceptions */
        
        l.lwz   r6,76(r1)               /* Recover ESR */
        l.lwz   r4,72(r1)               /* Recover EPCR */
        l.mtspr r0,r4,0x20              /* Restore ESR */
        l.mtspr r0,r6,0x40              /* Restore EPCR */
        l.lwz   r6,12(r1)
        l.lwz   r4,4(r1)

L2_2:
        l.lwz   r11,28(r1)
        l.lwz   r3,0(r1)
        l.addi  r1,r1,80
        l.rfe
        l.nop                           /* The document doesn't say this is
                                           a delay slot instruction, but the
                                           simulator doesn't work without this. */
        
.endproc ___standard_exception
        .def    ___standard_exception
        .val    .
        .scl    -1
        .endef

/****************************************************************************/
/* These constants must be in .text section in order to be                  */
/* properly addressed in code.                                              */

        PUBLIC(BOTTOM_OF_MEMORY)
SYM (BOTTOM_OF_MEMORY):
        .word   0x10000000       # Assume RAM @ 0 for the sim

        PUBLIC(TOP_OF_MEMORY)
SYM (TOP_OF_MEMORY):
        .word   0x10800000      # Assume RAM @ 0 for the sim

/****************************************************************************/

        /** Currently, about 57 of the 64 valid address locations
            are being used here. If you add code to the above
            routine, make sure it isn't more than 7 instructions
            or you will overflow into the reset vector. **/
                
        /****************************/
        /* Reset vector static code */
        /****************************/
        .org    0x100
.proc   ___rst
        .global ___rst
___rst:
        /* Set the stack pointer */
        l.movhi         r1,hi(_TOP_OF_MEMORY)
        l.ori           r1,r1,lo(_TOP_OF_MEMORY)
        l.lwz           r1,0(r1)   /* Dereference it */
        
        /* Set the frame pointer */
        l.add           r2,r0,r1

        l.mfspr         r3,r0,17        /* Get SR value */
        l.ori           r3,r3,2         /* Set exception enable bit */
        l.j             _start          /* Jump to main routine */
        l.mtspr         r0,r3,17        /* Enable exceptions (DELAY) */
.endproc ___rst

        /***********************************************************/
        /* Note:  right after the reset vector, we are going to    */
        /* place a table with the necessary values to initialize   */
        /* the memory controller. This pointer will be set and     */
        /* passed to the _start routine in r4. The first thing the */
        /* the _start routine will do is to initialize the memory  */
        /* controller. The code to initialze the memory controller */
        /* is expected to be larger than the 50 some odd           */
        /* instructions that are remaining here before the bus     */
        /* error vector, which is why it is left to the _start     */
        /* routine.                                                */
        /***********************************************************/
        
        /********************************/
        /* Bus Error vector static code */
        /********************************/
        .org    0x200
.proc   ___bus_error
        .global ___bus_error
___bus_error:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,8(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,2
        
.endproc ___bus_error

        /* Put _Internal_error_Occurred and _int_reenable here */
        /* No reason to waste space...it'll be filled with 0 if */
        /* we don't... */
        
        /********************************/
        /*   _Internal_error_Occurred   */
        /********************************/
                
.proc   __Internal_error_Occurred
        .def    __Internal_error_Occurred
        .val    __Internal_error_Occurred
        .scl    2
        .type   044
        .endef
        .global __Internal_error_Occurred
__Internal_error_Occurred:
        
        l.jal           __panic
        l.nop
        
.endproc __Internal_error_Occurred
        .def    __Internal_error_Occurred
        .val    .
        .scl    -1
        .endef

        
        /*********************/
        /*   _int_reenable   */
        /*********************/
                
.proc   __int_reenable
        .def    __int_reenable
        .val    __int_reenable
        .scl    2
        .type   044
        .endef
        .global __int_reenable
__int_reenable:
        
        l.mfspr r11,r0,17
        l.ori   r11,r11,0x04
        l.jr    r9
        l.mtspr r0,r11,17
        
.endproc __int_reenable
        .def    __int_reenable
        .val    .
        .scl    -1
        .endef

        /*********************&**/
        /*   ___user_function   */
        /************************/
                
.proc   ___user_function
        .def    ___user_function
        .val    ___user_function
        .scl    2
        .type   044
        .endef
        .global ___user_function
___user_function:

        /* r11 contains the address to call. We can
           modify r7, r8, r12, and r14 at will */
        
        l.movhi r7,hi(__Thread_Dispatch_disable_level)
        l.ori   r7,r7,lo(__Thread_Dispatch_disable_level)
        l.lwz   r8,0(r7)
        
        l.addi  r1,r1,-8        #  Stack must be DWORD aligned
        l.sw    0(r1),r9        #  Save the return address

        l.addi  r8,r8,1         # Increment __Thread_Dispatch...
        l.jalr  r11
        l.sw    0(r7),r8        # Disable thread dispatching
        
        /* Now, we need to determine if we need to
           service the RTEMS environment. RTEMS tries
           to draw a distinction between a RAW handler
           (where this isn't necessary) and an RTEMS
           handler. However, it appears almost all ISR's
           will not be RAW under this definition, and
           those that are will not honestly be hurt by
           the 20 or so extra cycles it will take to do
           the following code. If there is a very frequent
           interrupt, then it should probably be hard
           coded into the static routine anyway, rather
           than suffer the hit of calling it indirectly */

        /* Note:  RTEMS recommends incrementing and
           decrementing the _ISR_Nest_Level as well.
           We are specifically not doing this because
           in the Or1k architecture it is impossible
           to nest interrupts. Interrupts must run to
           completion before reenabling. If there is a
           significant task to be done, then it should
           run in a bottom half handler, similar to the
           way Linux works. In theory though, even if
           we do allow nested interrupts, there is no
           reason for this flag, as it seems to be for
           the purpose of restoring the normal stack in
           place of the interrupt stack. We don't use a
           separate exception stack, so this should not
           be an issue for us. */
                
        l.movhi r7,hi(__Thread_Dispatch_disable_level)
        l.ori   r7,r7,lo(__Thread_Dispatch_disable_level)
        l.lwz   r8,0(r7)
        l.addi  r8,r8,-1        # Decrement __Thread_Dispatch...
        l.sw    0(r7),r8        # Memory stall likely here...           

        l.sfeqi r8,0            # Skip if _Thread_Dispatch != 0
        l.bnf   L4_2
        l.movhi r7,hi(__Context_Switch_necessary)
        
        l.ori   r7,r7,lo(__Context_Switch_necessary)
        l.lwz   r8,0(r7)
                
        l.movhi r7,hi(__ISR_Signals_to_thread_executing)
        l.ori   r7,r7,lo(__ISR_Signals_to_thread_executing)
        l.lwz   r12,0(r7)

        l.sfeqi r8,0            # Skip if __Context... is false
        l.bf    L4_2
        l.movhi r14,hi(__Thread_Dispatch)
        
        l.sfeqi r12,0           # Skip if __ISR... is true
        l.bnf   L4_2
        l.ori   r14,r14,lo(__Thread_Dispatch)
        
        l.jalr  r14
        l.sw    0(r7),r0        # Set __ISR... to false
                
L4_2:                   
        l.lwz   r9,0(r1)        #  Recover the return address
        l.jr    r9
        l.addi  r1,r1,8         #  Reset the stack
        
.endproc ___user_function
        .def    ___user_function
        .val    .
        .scl    -1
        .endef

        
        /* Code wasted between here and 0x300 */
        
        /**************************************/
        /* Data Page Fault vector static code */
        /**************************************/
        .org    0x300
.proc   ___data_page_fault
        .global ___data_page_fault
___data_page_fault:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,12(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,3
.endproc ___data_page_fault

        /* Code wasted between here and 0x400 */
                
        /*********************************************/
        /* Instruction Page Fault vector static code */
        /*********************************************/
        .org    0x400
.proc   ___insn_page_fault
        .global ___insn_page_fault
___insn_page_fault:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,16(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,4
.endproc ___insn_page_fault

        /* Code wasted between here and 0x500 */
        
        /**************************************/
        /* Low Priority Interrupt static code */
        /**************************************/
        .org    0x500
.proc   ___low_priority_int
        .global ___low_priority_int
___low_priority_int:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.mfspr r3,r0,17                        # Get the SR
        l.addi  r11,r0,-5                       # r11 = 0xFFFFFFFB
        l.and   r11,r11,r3                      # Clear the EIR bit
        l.mtspr r0,r11,17                       # Set the SR w/o INT
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,20(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,5
.endproc ___low_priority_int

        /* Code wasted between here and 0x600 */
        
        /******************************************/
        /* Alignment Exception vector static code */
        /******************************************/
        .org    0x600
.proc   ___alignment_exception
        .global ___alignment_exception
___alignment_exception:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,24(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,6
.endproc ___alignment_exception

        /* Code wasted between here and 0x700 */
        
        /******************************************/
        /* Illegal Instruction vector static code */
        /******************************************/
        .org    0x700
.proc   ___illegal_instruction
        .global ___illegal_instruction
___illegal_instruction:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,28(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,7
.endproc ___illegal_instruction

        /* Code wasted between here and 0x800 */
        
        /***************************************/
        /* High Priority Interrupt static code */
        /***************************************/
        .org    0x800
.proc   ___high_priority_int
        .global ___high_priority_int
___high_priority_int:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.mfspr r3,r0,17                        # Get the SR
        l.addi  r11,r0,-5                       # r11 = 0xFFFFFFFB
        l.and   r11,r11,r3                      # Clear the EIR bit
        l.mtspr r0,r11,17                       # Set the SR w/o INT
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,32(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,8
.endproc ___high_priority_int

        /* Code wasted between here and 0x900 */
        
        /********************************/
        /* ITBL Miss vector static code */
        /********************************/
        .org    0x900
.proc   ___ITBL_miss_exception
        .global ___ITBL_miss_exception
___ITBL_miss_exception:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,36(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,9
.endproc ___ITBL_miss_exception

        /* Code wasted between here and 0xA00 */
        
        /********************************/
        /* DTBL Miss vector static code */
        /********************************/
        .org    0xA00
.proc   ___DTBL_miss_exception
        .global ___DTBL_miss_exception
___DTBL_miss_exception:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,40(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,10
.endproc ___DTBL_miss_exception

        /* Code wasted between here and 0xB00 */
        
        /**************************************/
        /* Range Exception vector static code */
        /**************************************/
        .org    0xB00
.proc   ___range_exception
        .global ___range_exception
___range_exception:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,44(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,11
.endproc ___range_exception

        /* Code wasted between here and 0xC00 */
        
        /**********************************/
        /* System Call vector static code */
        /**********************************/
        .org    0xC00
.proc   ___system_call
        .global ___system_call
___system_call:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,48(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,12
.endproc ___system_call

        /* Code wasted between here and 0xD00 */
        
        /**********************************/
        /* Breakpoint vector static code */
        /**********************************/
        .org    0xD00
.proc   ___breakpoint
        .global ___breakpoint
___breakpoint:

        /* In keeping with the necessary requirements for
           gdb to work, we are limiting this vector to
           only 2 statements, which effect an immediate
           return. At a later date, we may insert a debug
           monitor here that will do even more, but for
           now, this is all we want. */
        l.rfe
        l.nop

.endproc ___breakpoint

        /* Code wasted between here and 0xE00 */
        
        /*************************************/
        /* Trap Exception vector static code */
        /*************************************/
        .org    0xE00
.proc   ___trap_exception
        .global ___trap_exception
___trap_exception:
        l.addi  r1,r1,-80
        l.sw    0(r1),r3
        l.sw    28(r1),r11
        l.movhi r11,hi(_Or1k_Interrupt_Vectors)
        l.ori   r11,r11,lo(_Or1k_Interrupt_Vectors)
        l.lwz   r11,56(r11)
        l.j     ___standard_exception
        l.addi  r3,r0,14
.endproc ___trap_exception

        /* Code wasted between here and 0x2000 */
        
        /* Exceptions from 0xF00 to 0x1F00 are not defined */
        /* in the Or1k architecture. They should be filled */
        /* in here for other implementations.              */

        .org    0x2000          /* Start after exception vector table */
                
        /*********************/
        /*       start       */
        /*********************/

        /* This is where we jump to right after the reset exception
           handler. The system configuration information should
           be passed to us in a pointer in r4. Generally, the
           reset vector will call this routine directly, and
           the memory configuration information will be stored
           in the ROM/Flash image. It was decided no attempt
           would be made to automatically determine this
           information by probing, as the scheme would be too
           complex and inherently unreliable. */

        /* Initialize strings and structures here */    
L_program:      
        .ascii  "RTEMS_or1k\000"
        .align  4
L_argv: 
        .word   L_program
                                
.proc _start
        .def    _start
        .val    _start
        .scl    2
        .type   044
        .endef
        .global _start
_start: 

        /* Initialize the memory controller here!
           Discussions with Rudi have stated that
           the first few bytes of the ROM image should 
           contain a RAM map as opposed to trying to
           figure out what to do based on probing. This
           means a separate build of the OS for every
           possible board configuration, but there
           doesn't seem to be a better alternative. */

        /*** FIX ME! Initialize the external memory controller! ***/
        
        /* Move the data segment to RAM. Alternatively, we may
           copy the text segment as well. For now, we'll assume
           that the cache gives us sufficient performance that this
           is not necessary. It will be very easy to add this later.
         */     
        l.movhi         r4,hi(_etext)
        l.ori           r4,r4,lo(_etext)
        l.movhi         r5,hi(_BOTTOM_OF_MEMORY)
        l.ori           r5,r5,lo(_BOTTOM_OF_MEMORY)
        l.lwz           r5,0(r5)            # Dereference it
/*      l.add           r5,r5,r4            # Place it in memory above the text segment*/
        l.movhi         r3,hi(_edata)
        l.ori           r3,r3,lo(_edata)
        l.movhi         r5,hi(_data_start)
        l.ori           r5,r5,lo(_data_start)
        
L3_0:   
        l.lwz           r6,0(r4)
        l.addi          r5,r5,4
        l.addi          r4,r4,4
        l.sfeq          r3,r5
        l.bnf           L3_0
        l.sw            -4(r5),r6           # Minimize write after read stalls

        /* Initialize the BSS segment */
        l.movhi         r3,hi(__end)
        l.ori           r3,r3,lo(__end)
/*      l.sub           r3,r3,r4
        l.add           r3,r3,r5*/
        l.sfleu         r3,r5
        l.bf            L3_2               # Check for no BSS segment!
        l.nop
                
L3_1:
        l.addi          r5,r5,4
        l.sfeq          r5,r3
        l.bnf           L3_1
        l.sw            -4(r5),r0

L3_2:
        /* Tell everyone where the heap begins */
        l.movhi         r4,hi(__mem_end)
        l.ori           r4,r4,lo(__mem_end)
        l.sw            0(r4),r5
                        
        /* Due to what I consider a bug in RTEMS, the entire
           heap must be zeroed. I think this is the dumbest thing
           I've ever heard, but whatever turns them on. I'd rather
           see the code which depends on this behavior fixed. I
           myself have never written code which assumes zeroes
           will be returned from memory allocated from the heap. 
           Anyway, if I don't do it here, I have to set a flag in
           the CPU structure which then will do it anyway, but
           from less efficient C code! Zero from here to the
           stack pointer... One day when I'm old and gray maybe
           I'll set this to random values instead and fix
           whatever breaks. */
        
        l.sw            0(r5),r0
        l.sfeq          r5,r1
        l.bnf           L3_3
        l.addi          r5,r5,4 
        
L3_3:
        l.addi          r3,r0,1         /* Set argc to 1 */
        l.movhi         r4,hi(L_argv)   /* Initialize argv */
        l.ori           r4,r4,lo(L_argv)
        l.addi          r5,r5,0         /* Set envp to NULL */
                
        l.mfspr         r11,r0,17       /* Get SR value */
        l.ori           r11,r11,0x4     /* Set interrupt enable bit */
        l.jal           _boot_card      /* Boot up the card...run the OS */
        l.mtspr         r0,r11,17       /* Enable exceptions (DELAY) */
        
        /* We're done. We exited normally. Shut down. */
        l.jal           __exit
        l.nop
        
.endproc _start
        .def    _start
        .val    .
        .scl    -1
        .endef
        
        END_CODE