73 lines
3.4 KiB
ReStructuredText
73 lines
3.4 KiB
ReStructuredText
====================
|
|
Kernel driver ds2490
|
|
====================
|
|
|
|
Supported chips:
|
|
|
|
* Maxim DS2490 based
|
|
|
|
Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
|
|
|
|
|
|
Description
|
|
-----------
|
|
|
|
The Maxim/Dallas Semiconductor DS2490 is a chip
|
|
which allows to build USB <-> W1 bridges.
|
|
|
|
DS9490(R) is a USB <-> W1 bus master device
|
|
which has 0x81 family ID integrated chip and DS2490
|
|
low-level operational chip.
|
|
|
|
Notes and limitations.
|
|
|
|
- The weak pullup current is a minimum of 0.9mA and maximum of 6.0mA.
|
|
- The 5V strong pullup is supported with a minimum of 5.9mA and a
|
|
maximum of 30.4 mA. (From DS2490.pdf)
|
|
- The hardware will detect when devices are attached to the bus on the
|
|
next bus (reset?) operation, however only a message is printed as
|
|
the core w1 code doesn't make use of the information. Connecting
|
|
one device tends to give multiple new device notifications.
|
|
- The number of USB bus transactions could be reduced if w1_reset_send
|
|
was added to the API. The name is just a suggestion. It would take
|
|
a write buffer and a read buffer (along with sizes) as arguments.
|
|
The ds2490 block I/O command supports reset, write buffer, read
|
|
buffer, and strong pullup all in one command, instead of the current
|
|
1 reset bus, 2 write the match rom command and slave rom id, 3 block
|
|
write and read data. The write buffer needs to have the match rom
|
|
command and slave rom id prepended to the front of the requested
|
|
write buffer, both of which are known to the driver.
|
|
- The hardware supports normal, flexible, and overdrive bus
|
|
communication speeds, but only the normal is supported.
|
|
- The registered w1_bus_master functions don't define error
|
|
conditions. If a bus search is in progress and the ds2490 is
|
|
removed it can produce a good amount of error output before the bus
|
|
search finishes.
|
|
- The hardware supports detecting some error conditions, such as
|
|
short, alarming presence on reset, and no presence on reset, but the
|
|
driver doesn't query those values.
|
|
- The ds2490 specification doesn't cover short bulk in reads in
|
|
detail, but my observation is if fewer bytes are requested than are
|
|
available, the bulk read will return an error and the hardware will
|
|
clear the entire bulk in buffer. It would be possible to read the
|
|
maximum buffer size to not run into this error condition, only extra
|
|
bytes in the buffer is a logic error in the driver. The code should
|
|
match reads and writes as well as data sizes. Reads and
|
|
writes are serialized and the status verifies that the chip is idle
|
|
(and data is available) before the read is executed, so it should
|
|
not happen.
|
|
- Running x86_64 2.6.24 UHCI under qemu 0.9.0 under x86_64 2.6.22-rc6
|
|
with a OHCI controller, ds2490 running in the guest would operate
|
|
normally the first time the module was loaded after qemu attached
|
|
the ds2490 hardware, but if the module was unloaded, then reloaded
|
|
most of the time one of the bulk out or in, and usually the bulk in
|
|
would fail. qemu sets a 50ms timeout and the bulk in would timeout
|
|
even when the status shows data available. A bulk out write would
|
|
show a successful completion, but the ds2490 status register would
|
|
show 0 bytes written. Detaching qemu from the ds2490 hardware and
|
|
reattaching would clear the problem. usbmon output in the guest and
|
|
host did not explain the problem. My guess is a bug in either qemu
|
|
or the host OS and more likely the host OS.
|
|
|
|
03-06-2008 David Fries <David@Fries.net>
|