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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

/* Enable Cycle Counter and Nesting Of Interrupts */

#ifdef CONFIG_BFIN_SCRATCH_REG_CYCLES

R0 = SYSCFG_SNEN;

#else

R0 = SYSCFG_SNEN | SYSCFG_CCEN;

#endif

SYSCFG = R0;

這幾行代碼用于設置 SYSCFG 的值，關于 SYSCFG 這個寄存器， vdsp 文件這樣說：

The System Configuration Register (SYSCFG) shown in Figure 4-3 controls the configuration of the processor

對于 BF561 而言，只有 CCEN 和 SSSTEP 兩位有效，在這里將 CCEN 位設置為 1 ，表示要啟用 64 位的 cycle counter 。而對 SNEN 的置位將被忽略。

在啟用了 CCEN 之后， CYCLES 和 CYCLES2 兩個寄存器將開始統計 CCLK 的個數。

下面是 vdsp 文檔中對 CYCLES 和 CYCLES2 這兩個寄存器的一個說明：

The cycle counter counts CCLK cycles while the program is executing. All cycles, including execution, wait state, interrupts, and events, are counted while the processor is in User or Supervisor mode, but the cycle counter stops counting in Emulator mode.

The cycle counter is 64 bits wide and increments every cycle. The count value is stored in two 32-bit registers, CYCLES and CYCLES2 . The least significant 32 bits (LSBs) are stored in CYCLES. The most significant 32 bits (MSBs) are stored in CYCLES2 .

Note: To ensure read coherency, first read CYCLES , then CYCLES2 , and then CYCLES again, to detect if an overflow has occurred in the LSBs during the read operations.

In User mode, these two registers may be read, but not written. In Supervisor and Emulator modes, they are read/write registers.

To enable the cycle counters, set the CCEN bit in the SYSCFG register. The following example shows how to use the cycle counter:

R2 = 0;

CYCLES = R2;

CYCLES2 = R2;

R2 = SYSCFG;

BITSET(R2,1);

SYSCFG = R2;

/* Insert code to be benchmarked here. */

R2 = SYSCFG;

BITCLR(R2,1);

SYSCFG = R2;

通常這兩個寄存器可以用于性能統計。但是由于這兩個寄存器在幾種模式下均是可寫的，因此也可以將它們當成通用寄存器使用。在 uclinux 內核中，提供了一個叫 CONFIG_BFIN_SCRATCH_REG_CYCLES 的選項來控制 CYCLES 的用途：

config BFIN_SCRATCH_REG_CYCLES

bool "CYCLES"

help

Use the CYCLES register in the Blackfin exception handler

as a stack scratch register . This means you cannot

safely use the CYCLES performance registers on a Blackfin

board at anytime, but you can debug the system with a JTAG

ICE and use the NMI.

當設置了 CONFIG_BFIN_SCRATCH_REG_CYCLES 后，在 linux-2.6.x\arch\blackfin\mach-common\entry.S 文件中將 CYCLES 做為普通寄存器使用：

#if defined (CONFIG_BFIN_SCRATCH_REG_RETN)

# define EX_SCRATCH_REG RETN

#elif defined (CONFIG_BFIN_SCRATCH_REG_RETE)

# define EX_SCRATCH_REG RETE

#else

# define EX_SCRATCH_REG CYCLES

#endif

自然，在此時 CYCLES 是不應該自動計數的，因此 SYSCFG_CCEN 應該保持為 0 。

在 uclinux 內核代碼中搜索 CYCLES ，可以發現有以下幾個文件使用了它：

linux-2.6.x\drivers\char\bfin_timer_latency.c

linux-2.6.x\drivers\media\video\blackfin\blackfin_cam.c

linux-2.6.x\drivers\zaptel\bfsi-spi-framework.c

linux-2.6.x\drivers\zaptel\bfsi.c

當要使用這幾個驅動時，就一定需要使 SYSCFG_CCEN=1 。

1 參考資料

head.s 分析 (1) ：保存 u-boot 傳遞過來的指針 (2009-1-19)

head.s分析(2)：SYSCFG配置