1 ==================== 2 Kernel driver ds2490 3 ==================== 4 5 Supported chips: 6 7 * Maxim DS2490 based 8 9 Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru> 10 11 12 Description 13 ----------- 14 15 The Maxim/Dallas Semiconductor DS2490 is a chip 16 which allows to build USB <-> W1 bridges. 17 18 DS9490(R) is a USB <-> W1 bus master device 19 which has 0x81 family ID integrated chip and DS2490 20 low-level operational chip. 21 22 Notes and limitations. 23 24 - The weak pullup current is a minimum of 0.9mA and maximum of 6.0mA. 25 - The 5V strong pullup is supported with a minimum of 5.9mA and a 26 maximum of 30.4 mA. (From DS2490.pdf) 27 - The hardware will detect when devices are attached to the bus on the 28 next bus (reset?) operation, however only a message is printed as 29 the core w1 code doesn't make use of the information. Connecting 30 one device tends to give multiple new device notifications. 31 - The number of USB bus transactions could be reduced if w1_reset_send 32 was added to the API. The name is just a suggestion. It would take 33 a write buffer and a read buffer (along with sizes) as arguments. 34 The ds2490 block I/O command supports reset, write buffer, read 35 buffer, and strong pullup all in one command, instead of the current 36 1 reset bus, 2 write the match rom command and slave rom id, 3 block 37 write and read data. The write buffer needs to have the match rom 38 command and slave rom id prepended to the front of the requested 39 write buffer, both of which are known to the driver. 40 - The hardware supports normal, flexible, and overdrive bus 41 communication speeds, but only the normal is supported. 42 - The registered w1_bus_master functions don't define error 43 conditions. If a bus search is in progress and the ds2490 is 44 removed it can produce a good amount of error output before the bus 45 search finishes. 46 - The hardware supports detecting some error conditions, such as 47 short, alarming presence on reset, and no presence on reset, but the 48 driver doesn't query those values. 49 - The ds2490 specification doesn't cover short bulk in reads in 50 detail, but my observation is if fewer bytes are requested than are 51 available, the bulk read will return an error and the hardware will 52 clear the entire bulk in buffer. It would be possible to read the 53 maximum buffer size to not run into this error condition, only extra 54 bytes in the buffer is a logic error in the driver. The code should 55 match reads and writes as well as data sizes. Reads and 56 writes are serialized and the status verifies that the chip is idle 57 (and data is available) before the read is executed, so it should 58 not happen. 59 - Running x86_64 2.6.24 UHCI under qemu 0.9.0 under x86_64 2.6.22-rc6 60 with a OHCI controller, ds2490 running in the guest would operate 61 normally the first time the module was loaded after qemu attached 62 the ds2490 hardware, but if the module was unloaded, then reloaded 63 most of the time one of the bulk out or in, and usually the bulk in 64 would fail. qemu sets a 50ms timeout and the bulk in would timeout 65 even when the status shows data available. A bulk out write would 66 show a successful completion, but the ds2490 status register would 67 show 0 bytes written. Detaching qemu from the ds2490 hardware and 68 reattaching would clear the problem. usbmon output in the guest and 69 host did not explain the problem. My guess is a bug in either qemu 70 or the host OS and more likely the host OS. 71 72 03-06-2008 David Fries <David@Fries.net>
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