Hi!
Another specific scenario where slurp is required, I guess, is in
DS2480_set_baud, where we cannot rely on proper read-back, if the baud
rate changed.
So, as you say, slurp is probably required, and it's not worth trying to
do proper reading, which is bound to fail anyway.
Thus, my suggestion is to increase the slurp timeout so we can be sure
that we actually any pending bytes.
If slurp is only used during initial resets (which is the case for the
DS2480 and the LINK code, I haven't studied any others), then it is no
harm to increase this to say 100ms.
HOWEVER, if any other device-code is using slurp during the normal
communication flow, a longer timeout would of course hurt.
The thing with the FTDI parameter is that you cannot really change that
unless specific support for libftdi is added. Currently the DS2480 code
only works with a generic serial device, with no information on the
underlying hardware. So, hard to know when to apply ftdi changes, and
even harder to identify which port to change..
As discussed here previously, I've got some ftdi code in owfs working,
although for the LinkUSB. Should be trivial to port to the DS2480-code,
or probably most serial-based code. The question is if it makes sense to
add chip-specific code, when this is only usable if you actually use a
USB-serial-adapter built on that chip. In the LinkUSB case it makes more
sense, since the actual "1-wire-product" LinkUSB is built around that chip.
Anyway, by just raising the slurp timeout, we solve the main issue.
Controlling the FTDI timeout would however give some speed increase,
some simple tests shows that with a default of 16ms, the DS2480b reads
/28.xxxxxxx/power in ~77ms, vs 27ms with 1ms timeout.
Regarding 0-baud, I think it's only done from serial_powercycle, not
sure why though. Power-cycle adapters powered directly by the serial-port?
Since I don't know the use of the code, I cannot really say if this is
an issue worth addressing. B0 is defined in termios.h so it should
certainly be a valid value.
Johan
On 9/20/14 03:08 , Paul Alfille wrote:
Thank you, Johan, for the detailed tests.
The idea of "slurp" was to collect any pending serial traffic and
allow communication with the bus master to be synchronized. I agree
that matching expected response exactly is optimal, but that supposes
that you start from a known clean state. I found in some of my early
tests that old data was still delivered with the system was restarted.
Obviously, testing is hardware-specific. The timing was adjusted based
on my tests -- not very scientific.
It sounds like you think we should adjust the slurp time-out, and
perhaps some of the FTDI timing parameters. Also there is a 0-baud
issue which we should look at fixing on our end as well. Is it the
serial "BREAK" or baud changed that does it?
Paul
On Fri, Sep 19, 2014 at 2:57 AM, Johan Ström <jo...@stromnet.se
<mailto:jo...@stromnet.se>> wrote:
Hi,
I've noticed some problems using a FTDI based USB serial dongle
together
with a DS2480B based adapter (also known as DS9097U).
On startup the device was not recognized at all, complaining about
wrong
responses. Anyone else seen these issues?
I've debugged the problem and found the cause.
On startup, this is what happens:
DEBUG: ow_ds9097U.c:(287) Attempt 0 of 3 to initialize the DS9097U
TRAFFIC OUT <write> bus=0 (/dev/cua-labdesk)
Byte buffer anonymous, length=1
--000: C1
<.>
DEBUG: ow_ds9097U.c:(381) Send the initial reset to the bus master.
TRAFFIC OUT <write> bus=0 (/dev/cua-labdesk)
Byte buffer anonymous, length=1
--000: 71
<q>
TRAFFIC OUT <write> bus=0 (/dev/cua-labdesk)
Byte buffer anonymous, length=1
--000: 0F
<.>
DEBUG: ow_tcp_read.c:(64) attempt 1 bytes Time: 5.000000 seconds
TRAFFIC IN <NETREAD> bus=0 (/dev/cua-labdesk)
Byte buffer anonymous, length=1
--000: 70
<p>
DEBUG: ow_tcp_read.c:(114) read: 1 - 0 = 1
DEBUG: ow_ds9097U.c:(459) wrong response (70 not 00)
After each TRAFFIC OUT byte above, a COM_Slurp() is issued to read and
remove the response.
The response to the 71 command should be 70.. Which is what we see..
except that it fails to slurp those bytes, it's actually
reading them as the response to the next command.
After some further debugging and added printf statements, I
realize that
COM_slurp fails to read the bytes, and instead just timeouts (1ms).
I've been working on my pure-ftdi-branch for the LinkUSB, where I've
learned that the FTDI chips by default have a 16ms timeout for small
transfers, making them not very efficient when dealing with few bytes
like this.
Manually changing my USB-serial dongle's setting to 1ms with libftdi,
together with a slurp timeout of 2ms, seems to fix the problem.
However,
the slurp still times out, so I guess the accompanying COM_flush does
the trick.. Running with default 16ms FTDI setting, and a slurp
timeout
of 100ms, DOES succeed with reading the slurped data [1], and all
works
fine.
The "proper" way to solve this is probably to actually read the
bytes we
expect, not just hope that slurp catches them. However, this might be
problematic when changing bitrates etc?
The solution used above would be to give the slurp a longer timeout.
Besides that device init would take a few ms longer, would this
have any
other side effects?
>From the DS2480B code at least, it does not seem to slurp anywhere
except on device init.
For the record, the DS2480B works perfectly fine with my STLab 2 port
dongle (MosChip mos78x0 chip).. except that the stable FreeBSD-10
kernel
panics when setting baud rate 0, which happens sometimes in OWFS when
trying to forcefully reset. This was patched in
https://github.com/freebsd/freebsd/commit/120a212c4b16b5137d6acc436b8f5702a5f5bf35
but until the fix hits the mainline kernel, I'll have to go with
another
dongle.
Regards
Johan
[1]
This is how a proper session looks, with the responses slurped (FTDI
chip 16ms, COM_slurp timeout set to 100ms):
DEBUG: ow_ds9097U.c:(287) Attempt 0 of 3 to initialize the DS9097U
TRAFFIC OUT <write> bus=0 (/dev/cua-labdesk)
Byte buffer anonymous, length=1
--000: C1
<.>
TRAFFIC IN <slurp> bus=0 (/dev/cua-labdesk)
Byte buffer anonymous, length=1
--000: CD
<.>
Slurp timeout 100000 us..
DEBUG: ow_ds9097U.c:(381) Send the initial reset to the bus master.
TRAFFIC OUT <write> bus=0 (/dev/cua-labdesk)
Byte buffer anonymous, length=1
--000: 71
<q>
TRAFFIC IN <slurp> bus=0 (/dev/cua-labdesk)
Byte buffer anonymous, length=1
--000: 70
<p>
Slurp timeout 100000 us..
TRAFFIC OUT <write> bus=0 (/dev/cua-labdesk)
Byte buffer anonymous, length=1
--000: 0F
<.>
DEBUG: ow_tcp_read.c:(64) attempt 1 bytes Time: 5.000000 seconds
TRAFFIC IN <NETREAD> bus=0 (/dev/cua-labdesk)
Byte buffer anonymous, length=1
--000: 00
<.>
DEBUG: ow_tcp_read.c:(114) read: 1 - 0 = 1
DEBUG: ow_com_read.c:(83) COM_read, read 1 bytes.
read_get=16302.000000us, tcdrain=0.000000us: 1
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