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entation&nbsp;of&nbsp;this&nbsp;function.&nbsp;$(TOPDIR)/include/asm/bootinfo.h&nbsp;contains&nbsp;entries&nbsp;<br />
&nbsp;for&nbsp;the&nbsp;cputype&nbsp;(MYCPU)&nbsp;and&nbsp;machine&nbsp;group&nbsp;(MY_MACH_GROUP).&nbsp;The&nbsp;mips_&nbsp;cputyp&nbsp;<br />
e&nbsp;variable&nbsp;has&nbsp;to&nbsp;be&nbsp;updated&nbsp;in&nbsp;the&nbsp;cpu_probe&nbsp;function.&nbsp;This&nbsp;value&nbsp;is&nbsp;used&nbsp;l&nbsp;<br />
ater&nbsp;to&nbsp;determine&nbsp;the&nbsp;exception&nbsp;handling&nbsp;and&nbsp;MMU&nbsp;routines&nbsp;that&nbsp;need&nbsp;to&nbsp;be&nbsp;lo&nbsp;<br />
aded&nbsp;for&nbsp;the&nbsp;given&nbsp;CPU,&nbsp;as&nbsp;well&nbsp;as&nbsp;to&nbsp;get&nbsp;the&nbsp;CPU&nbsp;information&nbsp;in&nbsp;the&nbsp;/proc&nbsp;f&nbsp;<br />
ile&nbsp;system.&nbsp;<br />
Listing&nbsp;2:&nbsp;Code&nbsp;to&nbsp;probe&nbsp;cputype&nbsp;<br />
LEAF(cpu_probe)&nbsp;<br />
la&nbsp;&nbsp;t3,&nbsp;mips_cputype&nbsp;<br />
li&nbsp;&nbsp;t2,&nbsp;MYCPU&nbsp;&nbsp;/*&nbsp;include/asm-mips/bootinfo.h&nbsp;*/&nbsp;<br />
b&nbsp;&nbsp;probe_done&nbsp;<br />
sw&nbsp;&nbsp;t2,&nbsp;(t3)&nbsp;<br />
END(cpu_probe)&nbsp;<br />
The&nbsp;initial&nbsp;stack&nbsp;for&nbsp;the&nbsp;kernel&nbsp;is&nbsp;set&nbsp;up&nbsp;next.&nbsp;Then&nbsp;the&nbsp;bss&nbsp;section&nbsp;of&nbsp;the&nbsp;<br />
&nbsp;kernel&nbsp;image&nbsp;is&nbsp;cleared.&nbsp;Control&nbsp;then&nbsp;transfers&nbsp;to&nbsp;the&nbsp;prom_init()&nbsp;function&nbsp;<br />
.&nbsp;Then&nbsp;the&nbsp;TLB&nbsp;and&nbsp;caches&nbsp;are&nbsp;flushed&nbsp;and&nbsp;the&nbsp;cache&nbsp;manipulation&nbsp;functions&nbsp;a&nbsp;<br />
re&nbsp;set&nbsp;up&nbsp;inside&nbsp;loadmmu().&nbsp;Disabling&nbsp;of&nbsp;the&nbsp;coprocessors&nbsp;other&nbsp;than&nbsp;coproce&nbsp;<br />
ssor&nbsp;0&nbsp;is&nbsp;done&nbsp;next,&nbsp;followed&nbsp;by&nbsp;a&nbsp;jump&nbsp;to&nbsp;start_kernel().&nbsp;<br />
$(TOPDIR)/arch/MY_ARCH/mm&nbsp;contains&nbsp;the&nbsp;TLB&nbsp;routines&nbsp;and&nbsp;cache&nbsp;handling&nbsp;routi&nbsp;<br />
nes.&nbsp;<br />
Platform&nbsp;specific&nbsp;changes&nbsp;to&nbsp;the&nbsp;kernel&nbsp;code&nbsp;<br />
$(TOPDIR)/arch/MY_ARCH&nbsp;has&nbsp;a&nbsp;sub-directory&nbsp;for&nbsp;each&nbsp;target&nbsp;development&nbsp;platf&nbsp;<br />
orm&nbsp;that&nbsp;is&nbsp;supported.&nbsp;Create&nbsp;a&nbsp;MY_PLATFORM&nbsp;directory&nbsp;by&nbsp;copying&nbsp;a&nbsp;platform&nbsp;&nbsp;<br />
closest&nbsp;to&nbsp;your&nbsp;configuration.&nbsp;This&nbsp;directory&nbsp;should&nbsp;contain&nbsp;the&nbsp;interrupt&nbsp;h&nbsp;<br />
andling,&nbsp;timer,&nbsp;initialization,&nbsp;and&nbsp;setup&nbsp;routines&nbsp;for&nbsp;your&nbsp;specific&nbsp;platfor&nbsp;<br />
m.&nbsp;Create&nbsp;a&nbsp;MY_PLATFORM&nbsp;directory&nbsp;under&nbsp;$(TOPDIR)/include/asm.&nbsp;This&nbsp;director&nbsp;<br />
y&nbsp;is&nbsp;used&nbsp;to&nbsp;hold&nbsp;include&nbsp;files&nbsp;specific&nbsp;to&nbsp;your&nbsp;platform.&nbsp;<br />
The&nbsp;prom_init()&nbsp;function,&nbsp;which&nbsp;is&nbsp;part&nbsp;of&nbsp;$(TOPDIR)/arch/MY_ARCH/MY_PLATFOR&nbsp;<br />
M/prom.c&nbsp;(Listing&nbsp;3),&nbsp;modifies&nbsp;the&nbsp;command&nbsp;line&nbsp;string&nbsp;to&nbsp;add&nbsp;parameters&nbsp;tha&nbsp;<br />
t&nbsp;need&nbsp;to&nbsp;be&nbsp;passed&nbsp;to&nbsp;the&nbsp;kernel&nbsp;from&nbsp;the&nbsp;bootloader.&nbsp;The&nbsp;machine&nbsp;group&nbsp;and&nbsp;<br />
&nbsp;upper&nbsp;bound&nbsp;of&nbsp;usable&nbsp;memory&nbsp;are&nbsp;set&nbsp;up&nbsp;here.&nbsp;<br />
Listing&nbsp;3:&nbsp;PROM&nbsp;initialization&nbsp;<br />
int&nbsp;__init&nbsp;prom_init&nbsp;(int&nbsp;&nbsp;argc,&nbsp;char&nbsp;**argv,&nbsp;char&nbsp;**envp)&nbsp;<br />
{&nbsp;<br />
unsigned&nbsp;int&nbsp;mem_limit;&nbsp;<br />
//&nbsp;set&nbsp;upper&nbsp;limit&nbsp;to&nbsp;maximum&nbsp;physical&nbsp;RAM&nbsp;(32MB)&nbsp;<br />
mem_limit&nbsp;=&nbsp;32&nbsp;*&nbsp;1024&nbsp;*&nbsp;1024;&nbsp;<br />
//&nbsp;the&nbsp;bootloader&nbsp;usually&nbsp;passes&nbsp;us&nbsp;argc/argv[&nbsp;].&nbsp;<br />
//In&nbsp;the&nbsp;present&nbsp;case,&nbsp;these&nbsp;arguments&nbsp;are&nbsp;not&nbsp;<br />
//passed&nbsp;from&nbsp;the&nbsp;bootloader.&nbsp;The&nbsp;kernel&nbsp;wants&nbsp;<br />
//&nbsp;one&nbsp;big&nbsp;string.&nbsp;put&nbsp;it&nbsp;in&nbsp;arcs_cmdline,&nbsp;which&nbsp;<br />
later&nbsp;gets&nbsp;copied&nbsp;to&nbsp;command_line&nbsp;<br />
//(see&nbsp;arch/mips/kernel/setup.c)&nbsp;<br />
strcpy&nbsp;(arcs_cmdline,&nbsp;*root=/dev/ram*);&nbsp;<br />
mips_machgroup&nbsp;=&nbsp;MY_MACH_GROUP;&nbsp;<br />
//&nbsp;set&nbsp;the&nbsp;upper&nbsp;bound&nbsp;of&nbsp;usable&nbsp;memory&nbsp;<br />
mips_memory_upper&nbsp;=&nbsp;KSEG0&nbsp;+&nbsp;mem_limit;&nbsp;<br />
printk(*Detected&nbsp;%dMB&nbsp;of&nbsp;memory\n*,&nbsp;mem_limit&nbsp;&gt;&gt;&nbsp;20);&nbsp;<br />
return&nbsp;0;&nbsp;<br />
}&nbsp;<br />
Starting&nbsp;the&nbsp;kernel&nbsp;<br />
Listing&nbsp;4&nbsp;contains&nbsp;the&nbsp;first&nbsp;few&nbsp;interesting&nbsp;lines&nbsp;of&nbsp;the&nbsp;start_kernel()&nbsp;fun&nbsp;<br />
ction,&nbsp;located&nbsp;in&nbsp;$(TOPDIR)/init/main.c.&nbsp;<br />
Listing&nbsp;4:&nbsp;The&nbsp;beginning&nbsp;of&nbsp;the&nbsp;start_kernel&nbsp;function&nbsp;<br />
asmlinkage&nbsp;void&nbsp;__init&nbsp;start_kernel(void)&nbsp;<br />
{&nbsp;<br />
char&nbsp;*&nbsp;command_line;&nbsp;<br />
/*&nbsp;<br />
*&nbsp;Interrupts&nbsp;are&nbsp;still&nbsp;disabled.&nbsp;Do&nbsp;necessary&nbsp;setups,&nbsp;then&nbsp;<br />
*&nbsp;enable&nbsp;them&nbsp;<br />
*/&nbsp;<br />
lock_kernel();&nbsp;<br />
printk(linux_banner);&nbsp;<br />
setup_arch(&amp;command_line,&nbsp;&amp;memory_start,&nbsp;&amp;memory_end);&nbsp;<br />
memory_start&nbsp;=&nbsp;paging_init(memory_start,&nbsp;memory_end);&nbsp;<br />
trap_init();&nbsp;<br />
init_IRQ();&nbsp;<br />
sched_init();&nbsp;<br />
time_init();&nbsp;<br />
parse_options(command_line);&nbsp;<br />
.&nbsp;<br />
.&nbsp;<br />
.&nbsp;<br />
Listing&nbsp;5&nbsp;shows&nbsp;the&nbsp;setup_arch()&nbsp;function&nbsp;in&nbsp;$(TOPDIR)/arch/MY_ARCH/kernel/s&nbsp;<br />
etup.c.&nbsp;The&nbsp;board-specific&nbsp;setup&nbsp;function&nbsp;is&nbsp;called&nbsp;from&nbsp;here.&nbsp;The&nbsp;command&nbsp;l&nbsp;<br />
ine&nbsp;string&nbsp;and&nbsp;memory&nbsp;start&nbsp;and&nbsp;memory&nbsp;end&nbsp;are&nbsp;passed&nbsp;over&nbsp;to&nbsp;the&nbsp;caller&nbsp;of&nbsp;&nbsp;<br />
this&nbsp;function.&nbsp;The&nbsp;start&nbsp;and&nbsp;end&nbsp;addresses&nbsp;for&nbsp;the&nbsp;linked-in&nbsp;ramdisk&nbsp;image&nbsp;a&nbsp;<br />
re&nbsp;also&nbsp;updated&nbsp;here.&nbsp;<br />
Listing&nbsp;5:&nbsp;Architecture&nbsp;setup&nbsp;function&nbsp;<br />
__initfunc(void&nbsp;setup_arch(char&nbsp;**cmdline_p,&nbsp;<br />
unsigned&nbsp;long&nbsp;*&nbsp;memory_start_p,&nbsp;<br />
unsigned&nbsp;long&nbsp;*&nbsp;memory_end_p))&nbsp;<br />
{&nbsp;<br />
#ifdef&nbsp;CONFIG_BLK_DEV_INITRD&nbsp;<br />
#if&nbsp;CONFIG_BLK_DEV_INITRD_OFILE&nbsp;<br />
extern&nbsp;void&nbsp;*__rd_start,&nbsp;*__rd_end;&nbsp;<br />
#endif&nbsp;<br />
#endif&nbsp;<br />
myplatform_setup();&nbsp;<br />
strncpy(command_line,&nbsp;arcs_cmdline,&nbsp;CL_SIZE);&nbsp;<br />
*cmdline_p&nbsp;=&nbsp;command_line;&nbsp;<br />
*memory_start_p&nbsp;=&nbsp;(unsigned_long)&nbsp;&amp;_end;&nbsp;<br />
*memory_end_p&nbsp;=&nbsp;mips_memory_upper;&nbsp;<br />
#ifdef&nbsp;CONFIG_BLK_DEV_INITRD&nbsp;<br />
#if&nbsp;CONFIG_BLK_DEV_INITRD_OFILE&nbsp;<br />
//&nbsp;Use&nbsp;the&nbsp;linked-in&nbsp;ramdisk&nbsp;<br />
//&nbsp;image&nbsp;located&nbsp;at&nbsp;__rd_start.&nbsp;<br />
initrd_start&nbsp;=&nbsp;(unsigned&nbsp;long)&amp;__rd_start;&nbsp;<br />
initrd_end&nbsp;=&nbsp;(unsigned&nbsp;long)&amp;__rd_end;&nbsp;<br />
initrd_below_start_ok&nbsp;=&nbsp;1;&nbsp;<br />
if&nbsp;(initrd_end&nbsp;&gt;&nbsp;memory_end)&nbsp;<br />
{&nbsp;<br />
printk(*initrd&nbsp;extends&nbsp;beyond&nbsp;end&nbsp;of&nbsp;memory&nbsp;*&nbsp;<br />
*(0x%08lx&nbsp;&gt;&nbsp;0x%08lx)\ndisabling&nbsp;initrd\n*,&nbsp;<br />
initrd_end,&nbsp;memory_end);&nbsp;<br />
initrd_start&nbsp;=&nbsp;0;&nbsp;<br />
}&nbsp;<br />
#endif&nbsp;<br />
#endif&nbsp;<br />
}&nbsp;<br />
$(TOPDIR)/arch/MY_ARCH/MY_PLATFORM/setup.c&nbsp;contains&nbsp;the&nbsp;platform-specific&nbsp;in&nbsp;<br />
itialization&nbsp;code&nbsp;(Listing&nbsp;6).&nbsp;Here,&nbsp;the&nbsp;various&nbsp;base&nbsp;addresses&nbsp;and&nbsp;the&nbsp;plat&nbsp;<br />
form-specific&nbsp;RTC&nbsp;and&nbsp;PCI&nbsp;operations&nbsp;are&nbsp;set&nbsp;up.&nbsp;For&nbsp;PCI,&nbsp;the&nbsp;following&nbsp;seve&nbsp;<br />
n&nbsp;functions&nbsp;need&nbsp;to&nbsp;be&nbsp;implemented&nbsp;for&nbsp;the&nbsp;given&nbsp;platform:&nbsp;<br />
Listing&nbsp;6:&nbsp;Platform-specific&nbsp;initialization&nbsp;code&nbsp;<br />
__initfunc(void&nbsp;myplatform_setup(void))&nbsp;<br />
{&nbsp;<br />
irq_setup&nbsp;=&nbsp;myplatform_irq_setup;&nbsp;<br />
/*&nbsp;<br />
*&nbsp;mips_io_port_base&nbsp;is&nbsp;the&nbsp;beginning&nbsp;<br />
*of&nbsp;the&nbsp;address&nbsp;space&nbsp;to&nbsp;which&nbsp;x86&nbsp;<br />
*&nbsp;style&nbsp;I/O&nbsp;ports&nbsp;are&nbsp;mapped.&nbsp;<br />
*/&nbsp;<br />
mips_io_port_base&nbsp;=&nbsp;0xa0000000;&nbsp;<br />
/*&nbsp;<br />
*&nbsp;platform_io_mem_base&nbsp;is&nbsp;the&nbsp;<br />
*beginning&nbsp;of&nbsp;I/O&nbsp;bus&nbsp;memory&nbsp;space&nbsp;as&nbsp;<br />
*&nbsp;seen&nbsp;from&nbsp;the&nbsp;physical&nbsp;address&nbsp;bus.&nbsp;<br />
*This&nbsp;may&nbsp;or&nbsp;may&nbsp;not&nbsp;be&nbsp;ident-&nbsp;<br />
*&nbsp;ical&nbsp;to&nbsp;mips_io_port_base,&nbsp;e.g.&nbsp;the&nbsp;<br />
*former&nbsp;could&nbsp;point&nbsp;to&nbsp;the&nbsp;beginning&nbsp;of&nbsp;PCI&nbsp;<br />
*memory&nbsp;space&nbsp;while&nbsp;the&nbsp;latter&nbsp;might&nbsp;<br />
*indicate&nbsp;PCI&nbsp;I/O&nbsp;&nbsp;space.&nbsp;&nbsp;The&nbsp;two&nbsp;values&nbsp;are&nbsp;<br />
*used&nbsp;in&nbsp;different&nbsp;sets&nbsp;of&nbsp;macros.&nbsp;&nbsp;This&nbsp;<br />
*&nbsp;must&nbsp;be&nbsp;set&nbsp;to&nbsp;a&nbsp;correct&nbsp;value&nbsp;by&nbsp;the&nbsp;<br />
*platform&nbsp;setup&nbsp;code.&nbsp;<br />
*/&nbsp;<br />
platform_io_mem_base=0x10000000;&nbsp;<br />
/*&nbsp;<br />
*&nbsp;platform_mem_iobus_base&nbsp;is&nbsp;the&nbsp;<br />
*beginning&nbsp;of&nbsp;main&nbsp;memory&nbsp;as&nbsp;seen&nbsp;<br />
*&nbsp;from&nbsp;the&nbsp;I/O&nbsp;bus,&nbsp;and&nbsp;must&nbsp;be&nbsp;set&nbsp;<br />
*by&nbsp;the&nbsp;platform&nbsp;setup&nbsp;code.&nbsp;<br />
*/&nbsp;<br />
platform_mem_iobus_base=0x0;&nbsp;<br />
#ifdef&nbsp;CONFIG_REMOTE_DEBUG&nbsp;<br />
/*&nbsp;<br />
*&nbsp;Do&nbsp;the&nbsp;minimum&nbsp;necessary&nbsp;to&nbsp;set&nbsp;up&nbsp;debugging&nbsp;<br />
*/&nbsp;<br />
myplatform_kgdb_hook(0);&nbsp;<br />
remote_debug&nbsp;=&nbsp;1;&nbsp;<br />
#endif&nbsp;<br />
#ifdef&nbsp;CONFIG_BLK_DEV_IDE&nbsp;<br />