> On Aug 17, 2021, at 10:28 AM, Dave Tyson <dty...@anduin.org.uk> wrote: > > The device appears at address 0x77 (it's a BMP085) with i2cscan, the data > sheet indicates the read address=0xEF/write address=0xEE. I just put 0x77 in > the address field and assume the read/write bit on the wire is added based on > the op code (I2C_OP_WRITE, I2C_OP_READ etc).
Yes, that's correct. NetBSD natively addresses i2c devices using the 7-bit address **without** the read/write bit on the wire. As you noted, 0xef and 0xee shifted right 1 bit results in 0x77. > The device has R/O calibration data in 22 contiguous registers starting at > 0xAA->0xBF. Linux programs seem to grab the data in one go starting at 0xAA. > The other registers needed to initiate a sensor data grab are R/W - you write > a control byte into the 0xF4 register, wait a bit and then read the data from > another register set. > > A naive attempt to read the calibration data using: > > command = 0xAA ; > iie.iie_op = I2C_OP_READ ; > iie.iie_addr = 0x77 ; > iie.iie_cmd = &command ; > iie.iie_cmdlen = 1 ; > iie.iie_buf = &caldata[0] ; > iie.iie_buflen = 22; > if ((ioctl(iicfd, I2C_IOCTL_EXEC, &iie)) !=0) { > printf("read failed %d\n",errno) ; > exit(1) ; > } > > actually seemed to work OK, but I don't understand why! Looks right to me! I can explain to you why :-) Under the covers, NetBSD did the write and turn-around for you because you specified a "cmd". It performed a START (with the READ bit as 0), wrote the command bytes, then performed a REPEATED START with the READ bit set and then performed the READ. You probably should have used I2C_OP_READ_WITH_STOP because that was the end of your transaction. > I had expected to need a I2C_OP_WRITE first followed by a I2C_OP_READ_STOP. > The former would send a start bit, the device addr/write bit and the target > register. The latter would send a (re)start bit, device addr/read bit, pull > the data back and issue a stop. Maybe because the register I am addressing is > R/O there is no need for a write and what I am doing is correct... (or do I > need a I2C_OP_READ_STOP) > > Could someone explain what actually gets sent on the wire for the various ops: Ok, gotta page this one back into my brain from the archives, but here 'goes... > I2C_OP_READ If a "cmd" is specified, performs a START-WRITE, writes the cmd bytes, then performs a REPEATED-START-READ to read the data bytes (and performs a NACK after the last byte read). Errors result in a STOP condition. If no "cmd" is specified, similar to above except no START-WRITE is issued (REPEATED-START-READ and START-READ are the same on the wire). > I2C_OP_READ_WITH_STOP As above, but sets a STOP condition afterwards always. > I2C_OP_WRITE Sends a START-WRITE, then writes "cmd" bytes if provided and then data bytes. Errors result in a STOP condition. > I2C_OP_WRITE_WITH_STOP As above, but sets a STOP condition afterwards always. > I2C_OP_READ_BLOCK > I2C_OP_WRITE_BLOCK > > and what difference block operations make as man ICC(4) is terse to say the > least. The BLOCK operations are specific to SMBus block mode transfers. I don't know how much testing actually has been done with it (I know there are several i2c controller drivers that do not correctly support it). -- thorpej