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Post By：2019-3-17 12:13:00 [只看该作者]
我用6800的核心板通过spi接口与外部芯片通讯，程序基本是光盘里的示例程序，就是改了发送数据的内容，代码如下：
static const char *device = "/dev/spidev1.0";
static uint8_t mode = 3;
static uint8_t bits = 8;
static uint32_t speed = 5000000;
static uint16_t delay;
uint8_t tx[] = { 0x55, 0x00, 0x84, 0x00,0x08,0x00, 0x00,0x00, 0x00,0x00, 0x00,0x00, 0x00 };
uint8_t rx[ARRAY_SIZE(tx)];
struct spi_ioc_transfer tr[2];
void transfer(int fd)
{
int ret;
int i1;
printf( "transfer\n");
tr[0].tx_buf = (unsigned long)tx;
tr[0].rx_buf = (unsigned long)rx;
tr[0].len = ARRAY_SIZE(tx);
tr[0].delay_usecs = delay;
tr[0].speed_hz = speed;
tr[0].bits_per_word = bits;
/*tr[1].tx_buf = NULL;
tr[1].rx_buf = (unsigned long)rx;
tr[1].len = 1;
tr[1].delay_usecs = 0;
tr[1].speed_hz = speed;
tr[1].bits_per_word = bits;*/
ret = ioctl(fd, SPI_IOC_MESSAGE(1), tr );
if (ret < ARRAY_SIZE(tx) )
pabort("can't send spi message");
printf("ret=%d\n", ret );
for( i1=0; i1<ret; i1++ )
printf("%.2X ", rx[i1] );
printf("\n");
}
int main( int argc, char *argv[] )
{
char wr_buf[]={ 0x1b,0x55,0x1f,0x0f,0xff,0x00,0x1f,0x0f, 0xff,0x00 };
char rd_buf[10];
int i;
int ret = 0;
int fd;
fd = open(device, O_RDWR);
if (fd < 0)
pabort("can't open device");
/*
* spi mode
*/
ret = ioctl(fd, SPI_IOC_WR_MODE, &mode);
if (ret == -1)
pabort("can't set spi mode");
ret = ioctl(fd, SPI_IOC_RD_MODE, &mode);
if (ret == -1)
pabort("can't get spi mode");
/*
* bits per word
*/
ret = ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &bits);
if (ret == -1)
pabort("can't set bits per word");
ret = ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits);
if (ret == -1)
pabort("can't get bits per word");
/*
* max speed hz
*/
ret = ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed);
if (ret == -1)
pabort("can't set max speed hz");
ret = ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed);
if (ret == -1)
pabort("can't get max speed hz");
printf("spi mode: %d\n", mode);
printf("bits per word: %d\n", bits);
printf("max speed: %d Hz (%d KHz)\n", speed, speed/1000);
if( argc > 1 )
{
if( write(fd, wr_buf, 2) != 2 )
perror("Write Error");
}
else
transfer( fd );
close(fd);
return ret;
}
程序运行后的显现是没有收到设备返回的数据，
命令行显示结果是：
用示波器监测CS和MOSI信号波形如下：红色是CS信号，蓝色是MOSI信号，发送的数据是正确的，但是发现CS信号在每发送一个字节后都会变为高电平，而不是在整个报文发送过程中始终保存低电平，可能就是这个问题导致了连接的spi芯片不响应。请问如何设置能够在一帧数据发送的全过程中，CS信号始终保持低电平。
另外我使用的通讯芯片，还要求在开始发送前，CS信号先保持低电平一段时间，如何通过程序手工控制CS信号的状态？
