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/*----------------------------------------------------------------

//                                                              //

//  start.S                                                     //

//                                                              //

//  This file is part of the Amber project                      //

//  http://www.opencores.org/project,amber                      //

//                                                              //

//  Description                                                 //

//  Assembly routines for boot-loader.                          //

//  As boot-loader is a stand-alone application, it needs a     //

//  simple start function written in assembly to call the       //

//  C code main() function.                                     //

//                                                              //

//  Author(s):                                                  //

//      - Conor Santifort, csantifort.amber@gmail.com           //

//                                                              //

//////////////////////////////////////////////////////////////////

//                                                              //

// Copyright (C) 2010 Authors and OPENCORES.ORG                 //

//                                                              //

// This source file may be used and distributed without         //

// restriction provided that this copyright statement is not    //

// removed from the file and that any derivative work contains  //

// the original copyright notice and the associated disclaimer. //

//                                                              //

// This source file is free software; you can redistribute it   //

// and/or modify it under the terms of the GNU Lesser General   //

// Public License as published by the Free Software Foundation; //

// either version 2.1 of the License, or (at your option) any   //

// later version.                                               //

//                                                              //

// This source is distributed in the hope that it will be       //

// useful, but WITHOUT ANY WARRANTY; without even the implied   //

// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR      //

// PURPOSE.  See the GNU Lesser General Public License for more //

// details.                                                     //

//                                                              //

// You should have received a copy of the GNU Lesser General    //

// Public License along with this source; if not, download it   //

// from http://www.opencores.org/lgpl.shtml                     //

//                                                              //

----------------------------------------------------------------*/

#include "amber_registers.h"

#include "address_map.h"

/* Defined in vmlinux/include/asm-arm/setup.h */

#define ATAG_CORE       0x54410001

#define ATAG_MEM        0x54410002

#define ATAG_INITRD     0x54410005

#define ATAG_RAMDISK    0x54410004

#define ATAG_NONE       0x00000000

#define ATAG_CORE_SIZE    ((2*4 + 3*4) >> 2)

#define ATAG_MEM_SIZE     ((2*4 + 2*4) >> 2)

#define ATAG_INITRD_SIZE  ((2*4 + 2*4) >> 2)

#define ATAG_RAMDISK_SIZE ((2*4 + 3*4) >> 2)

/* from vmlinux/arch/arm/kernel/compat.c */

#define FLAG_READONLY   1

/* from the list in wmlinux/arch/arm/tools/mach-types */

#define MACH_TYPE_A5K   11

        .section .text

        .globl  start

start:

        /* 0x00 Reset Interrupt vector address */

        b       startup

        /* 0x04 Undefined Instruction Interrupt vector address */

        b       _testfail

        /* 0x08 SWI Interrupt vector address */

        b       _testfail

        /* 0x0c Prefetch abort Interrupt vector address */

        b       _testfail

        /* 0x10 Data abort Interrupt vector address */

        b       _testfail

        b       _testfail

        /* 0x18 IRQ vector address */

        b       service_irq

        /* 0x1c FIRQ vector address */

        b       _testfail

        .global _restart

_restart:

        @ jump to address 0 in irq mode

        mov     pc, #0x00000002

        nop

        nop

        nop

startup:

        /* copy program to exec space */

        mov     r0, #0

        ldr     r1, AdrExecBase

1:      ldm     r0!, {r2-r9}

        stm     r1!, {r2-r9}

        cmp     r0, #0x4000

        bne     1b

        /* Fix the interrupt jump pointers */

        ldr     r0, AdrExecBase

        mov     r1, r0, lsr #2

        mov     r2, #0

2:      ldr     r3, [r2]

        orr     r3, r3, r1

        str     r3, [r2], #4

        cmp     r2, #0x1c

        bne     2b

        /* Jump to 2f but offset from ExecBase not current location */

3:      ldr     r0, AdrExecBase

        ldr     r1, AdrJumpPoint

        orr     r0, r0, r1

        mov     pc, r0

_jump_point:

        /* Switch to IRQ Mode */

        mov     r0, #0x00000002

        teqp    pc, r0

        /* Set IRQ Mode stack pointer */

        ldr     sp, AdrIRQStack

        /* Switch to SVC mode and Unset interrupt mask bits */

        mov     r0, #0x00000003

        teqp    pc, r0

        @ Enable the cache

        @ set region 24 to be uncached. Used for packet buffers

        mov     r0, #0xfeffffff

        mcr     15, 0, r0, cr3, cr0, 0   @ cacheable area

        mov     r0, #1

        mcr     15, 0, r0, cr2, cr0, 0   @ cache enable

        @ init SP

        ldr     sp, AdrStack

        @ Set 32MB memory mode

        ldr     r0, AdrMemCtrl

        mov     r1, #1

        str     r1, [r0]

        .extern main

        bl      main

        @ jump to program at r0

        .globl _jump_to_program

_jump_to_program:

        @ ----------------------------------------------

        @ Copy ATAG structure to AdrBootParams

        @ ----------------------------------------------

        ldr     r1, AdrBootParams

        ldr     r2, AdrATAGBase

        ldr     r3, AdeEndATAG

1:      cmp     r2, r3

        beq     2f

        ldr     r4, [r2], #4

        str     r4, [r1], #4

        b       1b

        @ Set memc page tables

2:      ldr     r2, AdrPageTabes

        mov     r3, #0

        mov     r4, #40

3:      str     r3,[r2],#4

        subs    r4, r4, #1

        bne     3b

        @ ----------------------------------------------

        @ jump to start of program in svc mode with interrupts disabled

        @ ----------------------------------------------

        mov     r4, r0

        orr     r4, #0x0c000003

        mov     r0, #0

        mov     pc, r4

service_irq:

        @ Save all registers to the stack

        stmfd   sp!, {r0-r12, lr}

        @ is it a timer interrupt ?

        ldr     r0, AdrInterruptStatus

        ldr     r1, [r0]

        ands    r2, r1, #0x20

        beq     1f  @ not timer int, jump

        .extern timer_interrupt

        bl timer_interrupt

        @ is it an ethernet interrupt ?

1:      ands    r2, r1, #0x100

        beq     2f  @ not ethmac int, jump

        .extern ethmac_interrupt

        bl ethmac_interrupt

2:      @ Restore all registers from the stack

        ldmfd   sp!, {r0-r12, lr}

        @ Jump straight back to normal execution

        subs    pc, lr, #4

/* _testfail: Used to terminate execution in Verilog simulations */

/* On the board just puts the processor into an infinite loop    */

        .globl _testfail

_testfail:

        ldr     r11, AdrTestStatus

        str     r0, [r11]

        b       _testfail

/* _testpass: Used to terminate execution in Verilog simulations */

/* On the board just puts the processor into an infinite loop    */

        .globl _testpass

_testpass:

        ldr     r11, AdrTestStatus

        mov     r10, #17

        str     r10, [r11]

        b       _testpass

/* _div: Integer division function */

        @ Divide r0 by r1

        @ Answer returned in r1

        .globl _div

        .globl __aeabi_idiv

__aeabi_idiv:

_div:

        stmdb   sp!, {r4, lr}

        @ set r4 to 1 if one of the two inputs is negative

        and     r2, r0, #0x80000000

        and     r3, r1, #0x80000000

        eor     r4, r2, r3

        @ Invert negative numbers

        tst     r0, #0x80000000

        mvnne   r0, r0

        addne   r0, r0, #1

        tst     r1, #0x80000000

        mvnne   r1, r1

        addne   r1, r1, #1

        @ divide r1 by r2, also use registers r0 and r4

        mov     r2, r1

        mov     r1, r0

        cmp      r2, #0

        beq      3f

        @ In order to divide r1 by r2, the first thing we need to do is to shift r2

        @ left by the necessary number of places. The easiest method of doing this

        @ is simply by trial and error - shift until we discover that r2 has become

        @ too big, then stop.

        mov      r0,#0     @ clear r0 to accumulate result

        mov      r3,#1     @ set bit 0 in r3, which will be

                           @ shifted left then right

1:      cmp      r3, #0    @ escape on error

        moveq    r3, #0x10000000

        beq      2f

        cmp      r2,r1

        movls    r2,r2,lsl#1

        movls    r3,r3,lsl#1

        bls      1b

        @ shift r2 left until it is about to be bigger than r1

        @ shift r3 left in parallel in order to flag how far we have to go

        @ r0 will be used to hold the result. The role of r3 is more complicated.

        @ In effect, we are using r3 to mark where the right-hand end of r2 has got to

        @ - if we shift r2 three places left, this will be indicated by a value of %1000

        @ in r3. However, we also add it to r0 every time we manage a successful subtraction,

        @ since it marks the position of the digit currently being calculated in the answer.

        @ In the binary example (50 ÷ 10) above, we shifted the '10' two places left,

        @ so at the time of the first subtraction, r3 would have been %100, at the time

        @ of the second (which failed) it would have been %10, and at the time of the

        @ third %1. Adding it to r0 after each successful subtraction would have

        @ given us, once again, the answer of %101!

        @ Now for the loop that actually does the work:

2:      cmp       r1,r2      @ carry set if r1>r2 (don't ask why)

        subcs     r1,r1,r2   @ subtract r2 from r1 if this would

                             @ give a positive answer

        addcs     r0,r0,r3   @ and add the current bit in r3 to

                             @ the accumulating answer in r0

        @ In subtraction (a cmp instruction simulates a subtraction in

        @ order to set the flags), if r1 - r2 gives a positive answer and no 'borrow'

        @ is required, the carry flag is set. This is required in order to make SBC

        @ (Subtract with Carry) work properly when used to carry out a 64-bit subtraction,

        @ but it is confusing!

        @ In this case, we are turning it to our advantage. The carry flag is set to

        @ indicate that a successful subtraction is possible, i.e. one that doesn't

        @ generate a negative result, and the two following instructions are carried

        @ out only when the condition Carry Set applies. Note that the 'S' on the end

        @ of these instructions is part of the 'CS' condition code and does not mean

        @ that they set the flags!

        movs      r3,r3,lsr #1    @ Shift r3 right into carry flag

        movcc     r2,r2,lsr #1    @ and if bit 0 of r3 was zero, also

                                  @ shift r2 right

        bcc       2b              @ If carry not clear, r3 has shifted

                                  @ back to where it started, and we

                                  @ can end

        @ if one of the inputs is negetive then return a negative result

        tst     r4, #0x80000000

        mvnne   r0, r0

        addne   r0, r0, #1

3:      ldmia   sp!, {r4, pc}^

/* strcpy: String copy function

    char * strcpy ( char * destination, const char * source );

    destination is returned

*/

        @ r0 points to destination

        @ r1 points to source string which terminates with a 0

        .globl strcpy

strcpy:

        stmdb   sp!, {r4-r6, lr}

        @ Use r6 to process the destination pointer.

        @ At the end of the function, r0 is returned, so need to preserve it

        mov     r6, r0

strcpy_main:

        @ unroll the loop 4 times

        ldrb    r3, [r1], #1

        strb    r3, [r6], #1

        cmp     r3, #0

        ldmeqia sp!, {r4-r6, pc}^

        ldrb    r3, [r1], #1

        strb    r3, [r6], #1

        cmp     r3, #0

        ldmeqia sp!, {r4-r6, pc}^

        ldrb    r3, [r1], #1

        strb    r3, [r6], #1

        cmp     r3, #0

        ldmeqia sp!, {r4-r6, pc}^

        ldrb    r3, [r1], #1

        strb    r3, [r6], #1

        cmp     r3, #0

        ldmeqia sp!, {r4-r6, pc}^

        b       strcpy_main

/* strncpy: String copy function */

        @ r0 points to destination

        @ r1 points to source string

        @ r2 is the number of bytes to copy

        .globl strncpy

strncpy:

        stmdb   sp!, {r4, lr}

        cmp     r2, #0

        beq     2f

        add     r4, r0, r2    @ set r4 to the address of the last byte copied

1:      ldrb    r3, [r1], #1

        strb    r3, [r0], #1

        cmp     r0,  r4

        bne     1b

2:      ldmia   sp!, {r4, pc}^

/* strncpy: String compare function */

        @ r0 points to first string

        @ r1 points to second string

        @ r2 is the number of bytes to compare

        @ return the difference if the strings don't match

        .globl strncmp

strncmp:

        stmdb   sp!, {r4, r5, r6, lr}

        @ check for 0 length

        cmp     r2, #0

        moveq   r0, #1

        beq     2f

        mov     r3, #0

1:      add     r3, r3,   #1

        ldrb    r4, [r0], #1

        ldrb    r5, [r1], #1

        subs    r6, r4, r5

        movne   r0, r6

        bne     2f

        cmp     r3, r2

        moveq   r0, #0

        beq     2f

        b       1b

2:      ldmia   sp!, {r4, r5, r6, pc}^

        .globl init_malloc

init_malloc:

        ldr     r0, AdrMallocBase

        ldr     r1, AdrMallocPointer

        str     r0, [r1]

        @ initialize the counter to 0

        ldr     r1, AdrMallocCount

        mov     r2, #0

        str     r2, [r1]

        mov     pc, lr

        /* void *malloc(size_t size); */

        .globl malloc

malloc:

        /* r0 contains the size of the object in bytes */

        ldr     r1, AdrMallocPointer

        ldr     r2, [r1]    /* r2 now containts the starting address of the next memory block to use */

        add     r3, r0, r2  /* r3 contains the address after the end of the new object */

        /* Round r3 up to the nearest 0x100 to keep memory aligned */

        tst     r3, #0xff

        beq     1f

        bic     r3, r3, #0xff

        add     r3, r3, #0x100

1:      str     r3, [r1]    /* Update the malloc pointer */

        mov     r0, r2      /* Return the address from before the pointer was updated */

        @ Update the block count

        ldr     r1, AdrMallocCount

        ldr     r2, [r1]

        add     r2, r2, #1

        str     r2, [r1]

        mov     pc, lr

/* stack at top of ddr3 memory space */

AdrJumpPoint:               .word _jump_point

AdrExecBase:                .word ADR_EXEC_BASE

AdrStack:                   .word ADR_STACK

AdrIRQStack:                .word ADR_IRQ_STACK

AdrMallocPointer:           .word ADR_MALLOC_POINTER

AdrMallocCount:             .word ADR_MALLOC_COUNT

AdrMallocBase:              .word ADR_MALLOC_BASE

AdrMemCtrl:                 .word ADR_AMBER_TEST_MEM_CTRL

AdrTestStatus:              .word ADR_AMBER_TEST_STATUS

AdrInterruptStatus:         .word ADR_AMBER_IC_IRQ0_STATUS

                            .align 2

AdrATAGBase:                .word ATAGBase

AdeEndATAG:                 .word EndATAG

ATAGBase:                   .word ATAG_CORE_SIZE

                            .word ATAG_CORE

                            .word FLAG_READONLY     @ flags

                            .word 4096              @ page size

                            .word 0x0               @ rootdev

                            .word ATAG_MEM_SIZE

                            .word ATAG_MEM

                            .word 32*1024*1024      @ size - 32MB

                            .word 0x0               @ start

                            .word ATAG_RAMDISK_SIZE

                            .word ATAG_RAMDISK

                            .word 1                 @ flags: bit 0 = load, bit 1 = prompt

                            .word 0x000000d0        @ size in 1k blocks

                            .word 0x00800000        @ physical address of start of ramdisk

                            .word ATAG_INITRD_SIZE

                            .word ATAG_INITRD

                            .word 0x02800000        @ virtual address of start of initrd image

                            .word 0x00032000        @ size = 200k

                            .word ATAG_NONE

                            .word 0x0

EndATAG:                    .word 0x0

AdrBootParams:              .word 0x7c000

AdrPageTabes:               .word 0x3f01000