I agree with this as well. For awhile now, I think there has been a
need for an I2C driver layer, which also can manage bus arbitration.
Retries is another good one to add to that.
Sterling
On 31 Aug 2018, at 17:32, Andrzej Kaczmarek wrote:
Hi all,
Seems like the majority already voted to go for retries in HAL, but
I'll add my opinion anyway: I do not think HAL is proper place to
include such logic.
I think HAL should only provide interfaces to hide differences between
underlying MCU hardware while read/write retry logic is something
driver should do (or any caller in general) since it can decide when
and if it makes sense to retry. This is what common error codes (so
#1) would allow to do. This does not however mean we can't have common
retry code. What we likely need is some bus-level driver/layer that
drivers will use instead of HAL directly so it can take care of
handling multiple devices on the same bus seamlessly (in general) and
also it would be the place where we can put extra common logic if
needed (like retries).
Best,
Andrzej
On Thu, Aug 30, 2018 at 3:59 AM Christopher Collins <ch...@runtime.io>
wrote:
Hello all,
I noticed the HAL master I2C API does not include any retry logic.
As
you probably know, in I2C, the default state of the SCL line is NACK.
This means an unresponsive peripheral is indistinguishable from one
that
is actively nacking the master's writes. If the master's writes are
being NACKed because the slave is simply not ready to receive data,
then
retrying seems like the appropriate solution.
I can think of two ways to add I2C retries. Each of them requires
changes:
(1) Delegate the retry logic to the code calling into the HAL
(e.g.,
drivers).
(2) Implement retry logic directly in the HAL.
The problem with (1) is that HAL implementations currently return
MCU-specific error codes. A generic driver cannot determine if a
retry
is in order just from inspecting the error code. If there were a
common
set of error codes that all HAL I2C implementations returned, drivers
would have the information they need. Actually, even ignoring the
subject of retries, I think common error codes here makes sense.
Re: (2) - I was thinking this could be implemented by adding two new
members to the `hal_i2c_master_data` struct that gets passed to every
master I2C function:
/**
* Total number of times to attempt the I2C operation. Certain
* failures get retried:
* o NACK received after sending address.
* o (if configured) NACK received after sending data byte.
*/
uint8_t tries;
/** Whether to retry when a data byte gets NACKed. */
uint8_t retry_on_dnack:1;
(I hate to complicate things with the `retry_on_dnack` member, but
some
peripherals seem to become unresponsive in the middle of a
transaction.)
Since these additions are members of a struct, rather than new
function
parameters, this change would be mostly backwards-compatible. There
is
still a problem here, though: code that doesn't zero-out the
`hal_i2c_master_data` struct will likely get retries when it isn't
expecting them, which could conceivably be a problem.
I am leaning towards (1). Thoughts?
Thanks,
Chris
