Based on kernel version 3.9. Page generated on 2013-05-02 23:17 EST.
1 Kernel driver ds2490 2 ==================== 3 4 Supported chips: 5 * Maxim DS2490 based 6 7 Author: Evgeniy Polyakov <firstname.lastname@example.org> 8 9 10 Description 11 ----------- 12 13 The Maxim/Dallas Semiconductor DS2490 is a chip 14 which allows to build USB <-> W1 bridges. 15 16 DS9490(R) is a USB <-> W1 bus master device 17 which has 0x81 family ID integrated chip and DS2490 18 low-level operational chip. 19 20 Notes and limitations. 21 - The weak pullup current is a minimum of 0.9mA and maximum of 6.0mA. 22 - The 5V strong pullup is supported with a minimum of 5.9mA and a 23 maximum of 30.4 mA. (From DS2490.pdf) 24 - While the ds2490 supports a hardware search the code doesn't take 25 advantage of it (in tested case it only returned first device). 26 - The hardware will detect when devices are attached to the bus on the 27 next bus (reset?) operation, however only a message is printed as 28 the core w1 code doesn't make use of the information. Connecting 29 one device tends to give multiple new device notifications. 30 - The number of USB bus transactions could be reduced if w1_reset_send 31 was added to the API. The name is just a suggestion. It would take 32 a write buffer and a read buffer (along with sizes) as arguments. 33 The ds2490 block I/O command supports reset, write buffer, read 34 buffer, and strong pullup all in one command, instead of the current 35 1 reset bus, 2 write the match rom command and slave rom id, 3 block 36 write and read data. The write buffer needs to have the match rom 37 command and slave rom id prepended to the front of the requested 38 write buffer, both of which are known to the driver. 39 - The hardware supports normal, flexible, and overdrive bus 40 communication speeds, but only the normal is supported. 41 - The registered w1_bus_master functions don't define error 42 conditions. If a bus search is in progress and the ds2490 is 43 removed it can produce a good amount of error output before the bus 44 search finishes. 45 - The hardware supports detecting some error conditions, such as 46 short, alarming presence on reset, and no presence on reset, but the 47 driver doesn't query those values. 48 - The ds2490 specification doesn't cover short bulk in reads in 49 detail, but my observation is if fewer bytes are requested than are 50 available, the bulk read will return an error and the hardware will 51 clear the entire bulk in buffer. It would be possible to read the 52 maximum buffer size to not run into this error condition, only extra 53 bytes in the buffer is a logic error in the driver. The code should 54 should match reads and writes as well as data sizes. Reads and 55 writes are serialized and the status verifies that the chip is idle 56 (and data is available) before the read is executed, so it should 57 not happen. 58 - Running x86_64 2.6.24 UHCI under qemu 0.9.0 under x86_64 2.6.22-rc6 59 with a OHCI controller, ds2490 running in the guest would operate 60 normally the first time the module was loaded after qemu attached 61 the ds2490 hardware, but if the module was unloaded, then reloaded 62 most of the time one of the bulk out or in, and usually the bulk in 63 would fail. qemu sets a 50ms timeout and the bulk in would timeout 64 even when the status shows data available. A bulk out write would 65 show a successful completion, but the ds2490 status register would 66 show 0 bytes written. Detaching qemu from the ds2490 hardware and 67 reattaching would clear the problem. usbmon output in the guest and 68 host did not explain the problem. My guess is a bug in either qemu 69 or the host OS and more likely the host OS. 70 -- 03-06-2008 David Fries <David@Fries.net>