c - 如何为嵌入式系统优化此图像复制功能

Question

下面的函数使用 read_page(pageIter, pageArr, PAGESIZE) 一次读取一页图像，并在 DOUT 和 CCLK 引脚上输出数据。

有人告诉我它效率低下，但我似乎找不到让它更快的方法。它基本上是一个管道，在两个内存空间之间的 64 针 uProcessor 上运行。一个持有图像，另一个接收图像。

我使用了 register 关键字，删除了数组索引并替换为指针运算，但它需要更快。

谢谢!

/*
Port C Pin Out
*/
#define     BIT0        0x01    // CCLK
#define     BIT1        0x02    // CS_B
#define     BIT2        0x04    // INIT_B
#define     BIT3        0x08    // PROG_B
#define     BIT4        0x10    // RDRW_B
#define     BIT5        0x20    // BUSY_OUT
#define     BIT6        0x40    // DONE
#define     BIT7        0x80    // DOUT (DIN)

/*
PAGE
*/

#define     PAGESIZE    1024    // Example

void copyImage(ulong startAddress, ulong endAddress)
  {
  ulong pageIter;
  uchar *eByte, *byteIter, pageArr[PAGESIZE];
  register uchar bitIter, portCvar;
  portCvar = PORTC;
  /* Loops through pages in an image using ulong type*/
  for(pageIter = startAddress ;  pageIter <= endAddress ; pageIter += PAGESIZE)
    {
    read_page(pageIter, pageArr, PAGESIZE);
    eByte = pageArr+PAGESIZE;
    /* Loops through bytes in a page using pointer to uchar (pointer to a byte)*/
    for(byteIter = pageArr; byteIter <= eByte; byteIter++)
      {
      /* Loops through bits in byte and writes to PORTC - DIN ANC CCLK  */
      for(bitIter = 0x01; bitIter != 0x00; bitIter = bitIter << 1)
        {
        PORTC = portCvar | BIT0;
        (bitIter & *byteIter) ? (PORTC = portCvar & ~BIT7) : (PORTC = portCvar | BIT7);
        PORTC = portCvar & ~BIT0;
        }
      }
    }
  }

Answer 1

也许你可以通过像这样展开每个字节的传输来加快速度

PORTC = clock_1; PORTC = (value & 0x01 ? data1 : data0); PORTC = clock_0;
PORTC = clock_1; PORTC = (value & 0x02 ? data1 : data0); PORTC = clock_0;
PORTC = clock_1; PORTC = (value & 0x04 ? data1 : data0); PORTC = clock_0;
PORTC = clock_1; PORTC = (value & 0x08 ? data1 : data0); PORTC = clock_0;
PORTC = clock_1; PORTC = (value & 0x10 ? data1 : data0); PORTC = clock_0;
PORTC = clock_1; PORTC = (value & 0x20 ? data1 : data0); PORTC = clock_0;
PORTC = clock_1; PORTC = (value & 0x40 ? data1 : data0); PORTC = clock_0;
PORTC = clock_1; PORTC = (value & 0x80 ? data1 : data0); PORTC = clock_0;

在图像循环外进行一次预计算之后

unsigned char clock_1 = portC | BIT0;
unsigned char clock_0 = portC & ~BIT0;
unsigned char data1 = portC | BIT7;
unsigned char data0 = portC & ~BIT7;