RE: Bus Reset
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From: Mark K. <mk...@co...> - 2000-04-12 20:28:05
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Jeff, In general I agree with you, but it may in practice not be that simple... 1394 OHCI requires the use of a 1394a Phy. The problem is that 1394a was just approved within the last month, and while the spec has been stable for some time, there is no guarantee that everyone's 1394a Phys are truly compatible with the 1394a spec. There is usually a period of time where new hardware is getting released and the market determines, over time, what works and what doesn't. Keep in mind that much of the hardware we are looking at today may not have been placed under significant enough scrutiny to truly be deemed 'compliant'. This said, 1394a defines a new state called 'disabled'. If the Phy on your card is somehow in the disabled state, then the spec says it is not capable of detecting any signals. (Don't ask me how your Phy got into this state! I'm just suggesting that if the driver isn't careful there could be a problem here that is detectable and correctable in software that we would not be addressing today.) If this is the case, then the answer to your question is "No. There would not be a hardware reset". (At least the way I read the spec....) Keep plugging away and I'm sure you'll find the clue that helps the code guys (I'm a hardware guy) get the problem resolved. With best regards, Mark -----Original Message----- From: Jeff Mak [mailto:Jef...@ef...] Sent: Wednesday, April 12, 2000 11:07 AM To: 'Mark Knecht'; 'lin...@li...' Subject: RE: Bus Reset Mark, Thanks for the information you provided. The bus reset interrupt would be generated to the driver when the firewire detects there is a change in condition, right? In this case, I am thinking should it be controlled by hardware side (Firewire card itself) rather than checking port status register? Thanks, Jeff -----Original Message----- From: Mark Knecht [ mailto:mk...@co...] Sent: Wednesday, April 12, 2000 9:37 AM To: Jeff Mak; 'lin...@li...' Subject: RE: Bus Reset The Port Status Registers of a 1394a Phy provide the following indications: Connected - Is the cable attached to another 1394 device? Bias - Is that device providing TPBIAS? Disabled - Is this port of our Phy enabled or disabled? The use of these bits was envisioned as providing the information necessary to answer the questions you posed Jeff. I am unclear whether the Linux 1394 driver is taking advantage of these features at this time. It is possible that another thread having to do with the Sony OHCI implementation may be impacted by the state of these bits also. Cheers -----Original Message----- From: Jeff Mak [ mailto:Jef...@ef...] Sent: Tuesday, April 11, 2000 5:01 PM To: 'lin...@li...' Subject: Bus Reset For OHCI driver, whenever the target node is power off, bus reset would be generated. For IEEE1394, there are some power management i.e. the node is self-powered and this has been implemented in my target node. However, the bus reset signal is still generated causing my linux box cannot communicate with the target node anymore. My question is how to distinguish a target node from "power off" to "connection failed" i.e no bus reset would generate under "power off" connection ? Thanks, Jeff |