start_armboot()函數 是uboot中C語言代碼入口函數，從彙編語言跳轉到此
<span style="font-family:Courier New;">
178 _start_armboot: .word start_armboot</span>
完成uboot第二階段的一系列硬件初始化工作，然後轉入main函數
start_armboot()函數主要ARM系統的硬件和環境變量，包括Flash存儲器、FrameBuffer、網卡等，最後進入uboot應用程序主循環。
start_armboot()代碼如下：
<span style="font-family:Courier New;">
189 /*
190 * Breathe some life into the board...
191 *
192 * Initialize a serial port as console, and carry out some hardware
193 * tests.
194 *
195 * The first part of initialization is running from Flash memory;
196 * its main purpose is to initialize the RAM so that we
197 * can relocate the monitor code to RAM.
198 */
199
200 /*
201 * All attempts to come up with a "common" initialization sequence
202 * that works for all boards and architectures failed: some of the
203 * requirements are just _too_ different. To get rid of the resulting
204 * mess of board dependent #ifdef'ed code we now make the whole
205 * initialization sequence configurable to the user.
206 *
207 * The requirements for any new initalization function is simple: it
208 * receives a pointer to the "global data" structure as it's only
209 * argument, and returns an integer return code, where 0 means
210 * "continue" and != 0 means "fatal error, hang the system".
211 */
</span><span style="font-family:Courier New;">
212 typedef int (init_fnc_t) (void);
213
214 int print_cpuinfo (void); /* test-only */
215
216 init_fnc_t *init_sequence[] = {
217 cpu_init, /* basic cpu dependent setup */
218 board_init, /* basic board dependent setup */
219 interrupt_init, /* set up exceptions */
220 env_init, /* initialize environment */
221 init_baudrate, /* initialze baudrate settings */
222 serial_init, /* serial communications setup */
223 console_init_f, /* stage 1 init of console */
224 display_banner, /* say that we are here */
225 #if defined(CONFIG_DISPLAY_CPUINFO)
226 print_cpuinfo, /* display cpu info (and speed) */
227 #endif
228 #if defined(CONFIG_DISPLAY_BOARDINFO)
229 checkboard, /* display board info */
230 #endif
231 dram_init, /* configure available RAM banks */
232 display_dram_config,
233 NULL,
234 };
235
</span><span style="font-family:Courier New;">
236 void start_armboot (void)
237 {
238 init_fnc_t **init_fnc_ptr;
239 char *s;
240 #ifndef CFG_NO_FLASH
241 ulong size;
242 #endif
243 #if defined(CONFIG_VFD) || defined(CONFIG_LCD)
244 unsigned long addr;
245 #endif
246
247 /* Pointer is writable since we allocated a register for it */
248 gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));
249 /* compiler optimization barrier needed for GCC >= 3.4 */
250 __asm__ __volatile__("": : :"memory");
251
252 memset ((void*)gd, 0, sizeof (gd_t));
253 gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));
254 memset (gd->bd, 0, sizeof (bd_t));
255
256 monitor_flash_len = _bss_start - _armboot_start;
257
258 for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {
259 if ((*init_fnc_ptr)() != 0) {
260 hang ();
261 }
262 }
263
264 #ifndef CFG_NO_FLASH
265 /* configure available FLASH banks */
266 size = flash_init ();
267 display_flash_config (size);
268 #endif /* CFG_NO_FLASH */
269
270 #ifdef CONFIG_VFD
271 # ifndef PAGE_SIZE
272 # define PAGE_SIZE 4096
273 # endif
274 /*
275 * reserve memory for VFD display (always full pages)
276 */
277 /* bss_end is defined in the board-specific linker script */
278 addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);
279 size = vfd_setmem (addr);
280 gd->fb_base = addr;
281 #endif /* CONFIG_VFD */
282
283 #ifdef CONFIG_LCD
284 # ifndef PAGE_SIZE
285 # define PAGE_SIZE 4096
286 # endif
287 /*
288 * reserve memory for LCD display (always full pages)
289 */
290 /* bss_end is defined in the board-specific linker script */
291 addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);
292 size = lcd_setmem (addr);
293 gd->fb_base = addr;
294 #endif /* CONFIG_LCD */
295
296 /* armboot_start is defined in the board-specific linker script */
297 mem_malloc_init (_armboot_start - CFG_MALLOC_LEN);
298
299 #if (CONFIG_COMMANDS & CFG_CMD_NAND)
300 puts ("NAND: ");
301 nand_init(); /* go init the NAND */
302 #endif
303
304 #ifdef CONFIG_HAS_DATAFLASH
305 AT91F_DataflashInit();
306 dataflash_print_info();
307 #endif
308
309 /* initialize environment */
310 env_relocate ();
311
312 #ifdef CONFIG_VFD
313 /* must do this after the framebuffer is allocated */
314 drv_vfd_init();
315 #endif /* CONFIG_VFD */
316
317 /* IP Address */
318 gd->bd->bi_ip_addr = getenv_IPaddr ("ipaddr");
319
320 /* MAC Address */
321 {
322 int i;
323 ulong reg;
324 char *s, *e;
325 char tmp[64];
326
327 i = getenv_r ("ethaddr", tmp, sizeof (tmp));
328 s = (i > 0) ? tmp : NULL;
329
330 for (reg = 0; reg < 6; ++reg) {
331 gd->bd->bi_enetaddr[reg] = s ? simple_strtoul (s, &e, 16) : 0;
332 if (s)
333 s = (*e) ? e + 1 : e;
334 }
335
336 #ifdef CONFIG_HAS_ETH1
337 i = getenv_r ("eth1addr", tmp, sizeof (tmp));
338 s = (i > 0) ? tmp : NULL;
339
340 for (reg = 0; reg < 6; ++reg) {
341 gd->bd->bi_enet1addr[reg] = s ? simple_strtoul (s, &e, 16) : 0;
342 if (s)
343 s = (*e) ? e + 1 : e;
344 }
345 #endif
346 }
347
348 devices_init (); /* get the devices list going. */
349
350 #ifdef CONFIG_CMC_PU2
351 load_sernum_ethaddr ();
352 #endif /* CONFIG_CMC_PU2 */
353
354 jumptable_init ();
355
356 console_init_r (); /* fully init console as a device */
357
358 #if defined(CONFIG_MISC_INIT_R)
359 /* miscellaneous platform dependent initialisations */
360 misc_init_r ();
361 #endif
362
363 /* enable exceptions */
364 enable_interrupts ();
365
366 /* Perform network card initialisation if necessary */
367 #ifdef CONFIG_DRIVER_CS8900
368 cs8900_get_enetaddr (gd->bd->bi_enetaddr);
369 #endif
370
371 #if defined(CONFIG_DRIVER_SMC91111) || defined (CONFIG_DRIVER_LAN91C96)
372 if (getenv ("ethaddr")) {
373 smc_set_mac_addr(gd->bd->bi_enetaddr);
374 }
375 #endif /* CONFIG_DRIVER_SMC91111 || CONFIG_DRIVER_LAN91C96 */
376
377 /* Initialize from environment */
378 if ((s = getenv ("loadaddr")) != NULL) {
379 load_addr = simple_strtoul (s, NULL, 16);
380 }
381 #if (CONFIG_COMMANDS & CFG_CMD_NET)
382 if ((s = getenv ("bootfile")) != NULL) {
383 copy_filename (BootFile, s, sizeof (BootFile));
384 }
385 #endif /* CFG_CMD_NET */
386
387 #ifdef BOARD_LATE_INIT
388 board_late_init ();
389 #endif
390 #if (CONFIG_COMMANDS & CFG_CMD_NET)
391 #if defined(CONFIG_NET_MULTI)
392 puts ("Net: ");
393 #endif
394 eth_initialize(gd->bd);
395 #endif
396 /* main_loop() can return to retry autoboot, if so just run it again. */
397 for (;;) {
398 main_loop ();
399 }
400
401 /* NOTREACHED - no way out of command loop except booting */
402 }
</span>