Hi Jonathan, Thank you for taking the time to answer. These devices are mostly used in automotive/aerospace industries where they usually require a continuous stream of data even if an error occurs. This is why we cannot just "drop the record" :). So, should we maybe think of a way of covering flags channel types? Regards, -Stefan On Du, 2019-03-24 at 18:00 +0000, Jonathan Cameron wrote: > > > On Wed, 20 Mar 2019 14:53:50 +0000 > "Popa, Stefan Serban" <StefanSerban.Popa@xxxxxxxxxx> wrote: > > > > > Hello, > > > > We are currently working on a new adis16495 IMU driver which is an > > upgrade > > from the adis16480 family: https://www.analog.com/media/en/technical-do > > cume > > ntation/data-sheets/ADIS16495.pdf. > > > > This new chip supports a feature called "Burst Read Function" (page 13 > > in > > the datasheet). The burst read function (BRF) provides a method for > > reading > > a batch of data (status, temperature, gyroscopes, accelerometers, time > > stamp/data counter, and CRC code), which does not require a stall > > time between each 16-bit segment and only requires one command > > on the DIN line to initiate. > > > > Most of the data read in this way can be attributed to a type of > > channel: > > IIO_TEMP, IIO_ANGL_VEL, IIO_ACCEL, etc. However, there is no equivalent > > for > > the status and CRC. The status register provides various error flags > > such > > as spi communication error, sensor failure, sync error, etc (Table 18 > > in > > the datasheet). This information together with the CRC error should be > > exposed to the user space. What is the best way to do it? > Ok, So this is not exactly unusual. The issue has always been defining > a remotely generic userspace ABI. > > > > > > > The most obvious way, but not necessarily the correct one, would be to > > add > > a new channel type called something like IIO_STATUS or IIO_FLAG. Is > > this > > acceptable? > No unfortunately. What does generic userspace do with it? > > Part of the problem is we don't have a channel type to cover flags in > general (if we had digital inputs packed into bytes we would at least > be slightly better off). > > > > > > > A more or less similar burst read function has been previously > > implemented > > as part of the adis16400 driver. Although a burst read will also > > produce > > diagnostic status data, it was ignored in the driver implementation. > Yup :) Couldn't figure out how to do it at the time. > > Normally these flags represent error conditions (if they map to events > in IIO then put them out like that). The problem has always been that > Linux doesn't actually have generic simple error event handling. > There is RAS handling for servers, but who runs it on embedded boards > except possibly for some form of EDAC. > > > > > > > Looking forward to any suggestion. > I'm not against us having meta data channels, but they pretty much need > to be as tightly defined as any other channel. The other side issue > here is it's a new 'huge' space. However, I'm not sure you are in > that territory here. Looks to me like status really means error. > If you get an error, mostly it's game over. If you get a CRC error > and want to check it, then drop the record and spit out a message. > > So I'm a little unconvinced as yet that there is anything we actually > can use in this status message. > > Jonathan > > > > > > > > -Stefan
