Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 Kernel driver ds2490 2 ==================== 3 4 Supported chips: 5 * Maxim DS2490 based 6 7 Author: Evgeniy Polyakov <email@example.com> 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 - The hardware will detect when devices are attached to the bus on the 25 next bus (reset?) operation, however only a message is printed as 26 the core w1 code doesn't make use of the information. Connecting 27 one device tends to give multiple new device notifications. 28 - The number of USB bus transactions could be reduced if w1_reset_send 29 was added to the API. The name is just a suggestion. It would take 30 a write buffer and a read buffer (along with sizes) as arguments. 31 The ds2490 block I/O command supports reset, write buffer, read 32 buffer, and strong pullup all in one command, instead of the current 33 1 reset bus, 2 write the match rom command and slave rom id, 3 block 34 write and read data. The write buffer needs to have the match rom 35 command and slave rom id prepended to the front of the requested 36 write buffer, both of which are known to the driver. 37 - The hardware supports normal, flexible, and overdrive bus 38 communication speeds, but only the normal is supported. 39 - The registered w1_bus_master functions don't define error 40 conditions. If a bus search is in progress and the ds2490 is 41 removed it can produce a good amount of error output before the bus 42 search finishes. 43 - The hardware supports detecting some error conditions, such as 44 short, alarming presence on reset, and no presence on reset, but the 45 driver doesn't query those values. 46 - The ds2490 specification doesn't cover short bulk in reads in 47 detail, but my observation is if fewer bytes are requested than are 48 available, the bulk read will return an error and the hardware will 49 clear the entire bulk in buffer. It would be possible to read the 50 maximum buffer size to not run into this error condition, only extra 51 bytes in the buffer is a logic error in the driver. The code should 52 should match reads and writes as well as data sizes. Reads and 53 writes are serialized and the status verifies that the chip is idle 54 (and data is available) before the read is executed, so it should 55 not happen. 56 - Running x86_64 2.6.24 UHCI under qemu 0.9.0 under x86_64 2.6.22-rc6 57 with a OHCI controller, ds2490 running in the guest would operate 58 normally the first time the module was loaded after qemu attached 59 the ds2490 hardware, but if the module was unloaded, then reloaded 60 most of the time one of the bulk out or in, and usually the bulk in 61 would fail. qemu sets a 50ms timeout and the bulk in would timeout 62 even when the status shows data available. A bulk out write would 63 show a successful completion, but the ds2490 status register would 64 show 0 bytes written. Detaching qemu from the ds2490 hardware and 65 reattaching would clear the problem. usbmon output in the guest and 66 host did not explain the problem. My guess is a bug in either qemu 67 or the host OS and more likely the host OS. 68 -- 03-06-2008 David Fries <David@Fries.net>
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