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本文適用于

ADI bf561 DSP

uclinux-2008r1.5-rc3 ( 移植到 vdsp5)

Visual DSP++ 5.0(update 5)

歡迎轉載，但請保留作者信息

sp += -12;

call _init_pda;

sp += 12;

init_pda 的定義在 linux-2.6.x\arch\blackfin\mm\init.c 文件中。這是 SMP 相關的代碼所調用的第一個函數。

PDA ，即 Per-processor Data Areas ，一看就知道是每個核的私有財產，呵呵。

asmlinkage void init_pda( void )

{

unsigned int cpu = raw_smp_processor_id();

/* Initialize the PDA fields holding references to other parts

of the memory. The content of such memory is still

undefined at the time of the call, we are only setting up

valid pointers to it. */

memset(cpu_pda, 0, sizeof (*cpu_pda));

#ifdef CONFIG_MPU

#else

write_pda(ipdt, ipdt_tables[cpu]);

#ifdef CONFIG_CPLB_INFO

write_pda(ipdt_swapcount, ipdt_swapcount_tables[cpu]);

write_pda(dpdt_swapcount, dpdt_swapcount_tables[cpu]);

#endif

write_pda(dpdt, dpdt_tables[cpu]);

#endif

write_pda(ex_stack, exception_stacks[cpu + 1]);

#ifdef CONFIG_SMP

write_pda(imask, 0x1f);

#endif

}

1.1.1 獲取 DSPID

首先，它調用了 raw_smp_processor_id 來獲取當前核的序號，對于 561 ，如果運行這段代碼的是 A 核，將返回 0 ， B 核則返回 1 。

#define raw_smp_processor_id() blackfin_core_id()

#define blackfin_core_id() (bfin_read_DSPID() & 0xff)

#define bfin_read_DSPID() bfin_read32(DSPID)

1.1.2 cpu_pda

cpu_pda 定義為：

#define cpu_pda (( struct blackfin_pda *)get_l1_scratch_start())

#define get_l1_scratch_start() get_l1_scratch_start_cpu(blackfin_core_id())

#define get_l1_scratch_start_cpu(cpu) \

({ unsigned long __addr; \

__addr = (cpu) ? L1_SCRATCH_COREB : L1_SCRATCH_COREA; \

__addr; })

即它將使用每個核各自的 l1 scratchpad(4k) 來存放私有數據。 cpu_pda 即指向這段存儲空間的最低位置，并將之轉換為 ( struct blackfin_pda *) 。看看這個結構體的定義：

/* Per-processor Data Areas are located at the start of the L1 scratch

memory, so that each can be accessed at a fixed address from the

current CPU. Used for SMP support and process stack checking. */

struct pda_task_info {

/* Points to the start of the stack. */

void *stack_start;

/* Not updated by the kernel; a user process can modify this to

keep track of the lowest address of the stack pointer during its

runtime. */

void *lowest_sp;

};

struct blackfin_pda { /* Per-processor Data Area */

struct pda_task_info task_info;

#ifdef CONFIG_SMP

unsigned long imask; /* Current IMASK value */

#endif

unsigned long *ipdt; /* Start of switchable I-CPLB table */

unsigned long *ipdt_swapcount; /* Number of swaps in ipdt */

unsigned long *dpdt; /* Start of switchable D-CPLB table */

unsigned long *dpdt_swapcount; /* Number of swaps in dpdt */

/*

* Single instructions can have multiple faults, which

* need to be handled by traps.c, in irq5. We store

* the exception cause to ensure we don't miss a

* double fault condition

*/

unsigned long ex_iptr;

unsigned long ex_optr;

unsigned long ex_buf[4];

unsigned long ex_imask; /* Saved imask from exception */

unsigned long *ex_stack; /* Exception stack space */

#ifdef ANOMALY_05000261

unsigned long last_cplb_fault_retx;

#endif

};

離 4K 的大小還遠著呢，還有擴展的潛力，呵呵。

1.1.3 write_pda

這個宏定義為：

#define write_pda(field, val) \

do { \

cpu_pda->field = val; \

} while (0)

就是對 cpu_pda 的各個字段賦值。

這里涉及的幾個數組，其定義如下：

u_long ipdt_tables[NR_CPUS][MAX_SWITCH_I_CPLBS+1];

u_long dpdt_tables[NR_CPUS][MAX_SWITCH_D_CPLBS+1];

#ifdef CONFIG_CPLB_INFO

u_long ipdt_swapcount_tables[NR_CPUS][MAX_SWITCH_I_CPLBS];

u_long dpdt_swapcount_tables[NR_CPUS][MAX_SWITCH_D_CPLBS];

#endif

extern unsigned long exception_stacks[NR_CPUS][1024];

head.s分析(18)：init_pda