问题
So I have 2 PCA9555 (16 channel digital I/O) chips connected to a small embedded device running Linux over i2c. The PCA9555 devices have 7 bit addresses 0100000 and 0100001.
When I power up the board, I run:
# modprobe i2c-i801
# modprobe i2c-dev
# i2cdetect -l
i2c-0 smbus SMBus I801 adapter at 0500 SMBus adapter
# i2cdump -y -r 0
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
... (Same for every line)
70: -- -- -- -- -- -- --
# dmesg|tail
i801_smbus 0000:00:1f.3 Transaction timeout
... (For every '--' in i2cdump, one of these errors outputted)
i801_smbus 0000:00:1f.3 Transaction timeout
So then I tried to write a simple program to set all pins on the first PCA9555 chip to output high:
char *file;
unsigned char buf[3];
int addr, fd;
file = "/dev/i2c-0";
addr = 0x20; /* 0100000 */
if((fd = open(file, O_RDWR)) < 0){
err(1, "open()");
}
if(ioctl(fd, I2C_SLAVE, addr) < 0){ /* also tried I2C_SLAVE_FORCE */
err(1, "ioctl()");
}
/* Set all digital I/Os to output */
buf[0] = 6;
buf[1] = 0x00;
buf[2] = 0x00;
if(write(fd, buf, 3) != 3){
err(1, "write() 1");
}
/* Set all outputs high */
buf[0] = 2;
buf[1] = 0xFF;
buf[2] = 0xFF;
if(write(fd, buf, 3) != 3){
err(1, "write() 2");
}
return 0;
Running this returns:
# ./i2c
./i2c: write() 1: Operation not supported
So I don't really understand what I'm doing wrong. Assuming the hardware is wired correctly where do I go from here?
回答1:
The i801 adapter only supports SMBUS transfers, and the Linux i2c core doesn't support arbitrary write calls on SMBUS adapters. You'll need to use i2c_smbus_write_word_data
. The kernel documentation doesn't go into detail on this, but that's the reason it recommends using SMBUS commands.
来源:https://stackoverflow.com/questions/5195991/writeing-to-i2c-device-operation-not-permitted