arch/nios/cpu/start.S

   1 /*
   2  * (C) Copyright 2003, Psyent Corporation <www.psyent.com>
   3  * Scott McNutt <smcnutt@psyent.com>
   4  *
   5  * See file CREDITS for list of people who contributed to this
   6  * project.
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU General Public License as
  10  * published by the Free Software Foundation; either version 2 of
  11  * the License, or (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
  21  * MA 02111-1307 USA
  22  */
  23
  24
  25 #include <config.h>
  26 #include <timestamp.h>
  27 #include <version.h>
  28
  29 #if !defined(CONFIG_IDENT_STRING)
  30 #define CONFIG_IDENT_STRING ""
  31 #endif
  32
  33 #define STATUS_INIT     0x8600          /* IE=1, IPRI=2 */
  34
  35 /*************************************************************************
  36  * RESTART
  37  ************************************************************************/
  38
  39         .text
  40         .global _start
  41
  42 _start:
  43         bsr     0f
  44         nop
  45         .long   _start
  46
  47         /* GERMS -- The "standard-32" configuration GERMS monitor looks
  48          * for the string "Nios" at flash_base + 0xc (actually it only
  49          * tests for 'N', 'i'). You can leave support for this in place
  50          * as it's only a few words.
  51          */
  52         . = _start + 0x000c
  53         .string "Nios"
  54
  55         .align 4
  56 0:
  57         /*
  58          * Early setup -- set cwp = HI_LIMIT, IPRI = 2, IE = 1 to
  59          * enable underflow exceptions. Disable cache.
  60          * NOTE: %o7 has return addr -- save in %g7 use later.
  61          */
  62         mov     %g7, %o7
  63
  64         pfx     2                       /* WVALID */
  65         rdctl   %g0
  66         lsri    %g0, 1
  67         pfx     %hi(STATUS_INIT)
  68         or      %g0, %lo(STATUS_INIT)
  69         wrctl   %g0                     /* update status */
  70         nop
  71
  72         /*
  73          * STACK
  74          */
  75         pfx     %hi(CONFIG_SYS_INIT_SP)
  76         movi    %sp, %lo(CONFIG_SYS_INIT_SP)
  77         pfx     %xhi(CONFIG_SYS_INIT_SP)
  78         movhi   %sp, %xlo(CONFIG_SYS_INIT_SP)
  79         mov     %fp, %sp
  80
  81         pfx     %hi(4*16)
  82         subi    %sp, %lo(4*16)          /* Space for reg window mgmt */
  83
  84         /*
  85          * RELOCATE -- %g7 has return addr from bsr at _start.
  86          */
  87         pfx     %hi(__u_boot_cmd_end)
  88         movi    %g5, %lo(__u_boot_cmd_end)
  89         pfx     %xhi(__u_boot_cmd_end)
  90         movhi   %g5, %xlo(__u_boot_cmd_end) /* %g5 <- end address */
  91
  92         lsli    %g7, 1                  /* mem = retaddr << 1 */
  93         mov     %g6, %g7
  94         subi    %g6, 4                  /* %g6 <- src addr */
  95         ld      %g7, [%g7]              /* %g7 <- dst addr */
  96
  97         /* No need to move text sections if we're already located
  98          * at the proper address.
  99          */
 100         cmp     %g7, %g6
 101         ifs     cc_z
 102         br      reloc
 103         nop                             /* delay slot */
 104
 105 1:      cmp     %g7, %g5
 106         skps    cc_nz
 107         br      2f
 108         nop                             /* delay slot */
 109
 110         ld      %g0, [%g6]
 111         addi    %g6, 4                  /* src++ */
 112         st      [%g7], %g0
 113         addi    %g7, 4                  /* dst++ */
 114         br      1b
 115         nop                             /* delay slot */
 116 2:
 117
 118         /*
 119          * Jump to relocation address
 120          */
 121          pfx    %hi(reloc@h)
 122          movi   %g0, %lo(reloc@h)
 123          pfx    %xhi(reloc@h)
 124          movhi  %g0, %xlo(reloc@h)
 125          jmp    %g0
 126          nop                            /* delay slot */
 127 reloc:
 128
 129         /*
 130          * CLEAR BSS
 131          */
 132         pfx     %hi(__bss_end)
 133         movi    %g5, %lo(__bss_end)
 134         pfx     %xhi(__bss_end)
 135         movhi   %g5, %xlo(__bss_end)    /* %g5 <- end address */
 136         pfx     %hi(__bss_start)
 137         movi    %g7, %lo(__bss_start)
 138         pfx     %xhi(__bss_start)
 139         movhi   %g7, %xlo(__bss_start)  /* %g7 <- end address */
 140
 141         movi    %g0, 0
 142 3:      cmp     %g7, %g5
 143         skps    cc_nz
 144         br      4f
 145         nop                             /* delay slot */
 146
 147         st      [%g7], %g0
 148         addi    %g7, 4                  /* (delay slot) dst++ */
 149         br      3b
 150         nop                             /* delay slot */
 151 4:
 152
 153         /*
 154          * INIT VECTOR TABLE
 155          */
 156         pfx     %hi(CONFIG_SYS_VECT_BASE)
 157         movi    %g0, %lo(CONFIG_SYS_VECT_BASE)
 158         pfx     %xhi(CONFIG_SYS_VECT_BASE)
 159         movhi   %g0, %xlo(CONFIG_SYS_VECT_BASE) /* dst */
 160         mov     %l0, %g0
 161
 162         pfx     %hi(_vectors)
 163         movi    %g1, %lo(_vectors)
 164         pfx     %xhi(_vectors)
 165         movhi   %g1, %xlo(_vectors)     /* src */
 166         bgen    %g2, 6                  /* cnt = 64 */
 167
 168         ldp     %g3, [%l0, 3]           /* bkpt vector */
 169         ldp     %g4, [%l0, 4]           /* single step vector */
 170
 171 5:      ld      %g7, [%g1]
 172         addi    %g1, 4                  /* src++ */
 173         st      [%g0], %g7
 174         addi    %g0, 4                  /* dst++ */
 175
 176         subi    %g2, 1                  /* cnt-- */
 177         ifrnz   %g2
 178         br      5b
 179         nop                             /* delay slot */
 180
 181 #if defined(CONFIG_ROM_STUBS)
 182         /* Restore the breakpoint and single step exception
 183          * vectors to their original values.
 184          */
 185         stp     [%l0,3], %g3            /* breakpoint */
 186         stp     [%l0,4], %g4            /* single step */
 187 #endif
 188
 189         /* For debug startup convenience ... software breakpoints
 190          * set prior to this point may not succeed ;-)
 191          */
 192         .global __start
 193 __start:
 194
 195         /*
 196          * Call board_init -- never returns
 197          */
 198         pfx     %hi(board_init@h)
 199         movi    %g1, %lo(board_init@h)
 200         pfx     %xhi(board_init@h)
 201         movhi   %g1, %xlo(board_init@h)
 202         call    %g1
 203         nop                             /* Delaly slot */
 204         /* NEVER RETURNS */
 205
 206 /*
 207  * dly_clks -- Nios doesn't have a time/clk reference for simple
 208  * delay loops, so we do our best by counting instruction cycles.
 209  * A control register that counts system clock cycles would be
 210  * a handy feature -- hint for Altera ;-)
 211  */
 212         .globl dly_clks
 213         /* Each loop is 4 instructions as delay slot is always
 214          * executed. Each instruction is approximately 4 clocks
 215          * (according to some lame info from Altera). So ...
 216          * ... each loop is about 16 clocks.
 217          */
 218
 219 dly_clks:
 220         lsri    %o0, 4                  /* cnt/16 */
 221
 222 8:      skprnz  %o0
 223         br      9f
 224         subi    %o0, 1                  /* cnt--, Delay slot */
 225         br      8b
 226         nop
 227
 228 9:      lret
 229         nop                             /* Delay slot */
 230
 231
 232         .data
 233         .globl  version_string
 234
 235 version_string:
 236         .ascii U_BOOT_VERSION
 237         .ascii " (", U_BOOT_DATE, " - ", U_BOOT_TIME, ")"
 238         .ascii CONFIG_IDENT_STRING, "\0"