Date: Thu, 3 May 2001 18:15:59 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: brett@lariat.org (Brett Glass) Cc: tlambert@primenet.com (Terry Lambert), dchulhan@uwi.tt (Dale Chulhan - Home), chat@FreeBSD.ORG (chat@FreeBSD.ORG) Subject: Re: Modem Woes Message-ID: <200105031815.LAA29153@usr05.primenet.com> In-Reply-To: <4.3.2.7.2.20010503114324.0459d260@localhost> from "Brett Glass" at May 03, 2001 11:49:37 AM
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> >In FreeBSD, COM ports can not share IRQs. > > Terry, this is not correct. I have several multiport cards > in which several UARTs share IRQs. They all run fine > under FreeBSD. Here's an excerpt from the kernel config of > one of them: Brett, these are multiport cards, which have interrupt coelescing logic on the multiport card, and for which the multiport card itself is the source of the interrupt, not the individual UART. As a result, while you are marking these things as "shared", from the driver perspective, from the perspective of the motherboard, they are _NOT_ shared. PC motherboards can not share ISA interrupts, period, unless they only enable the interrupts on one "shared" device at a time. This is an electrical fact, since the interrupts on ISA are _NOT_ level triggered and _can not be_ level triggered, because the orginal PC design left out 3 very inexpensive (even at the time) electronic components. > >If your modem is COM4: in Windows, it uses IRQ 3, which is > >already allocated to COM2:. > > Attempting to share IRQs between ports can cause an electrical > problem on the bus IF the ports are on two separate > ISA cards, because the IRQ lines on ISA are tri-state, not open > collector. But if the UARTS are on EISA or PCI cards, or > on the same card, an IRQ can be shared. By definition, the COM1 and COM2 ports are on the muli I/O chip in PC hardware, and are ISA devices. He _CAN NOT_ share a PCI and an ISA interrupt. > >Note that Windows can "share" IRQs 4 and 3 (COM1: IRQ 4, > >COM2: IRQ 3, COM3: IRQ 4, COM4: IRQ 3) because it does not > >open both COM1: and COM3: or COM2: and COM4: simultaneously. > > I've had comm ports that shared IRQs open simultaneously under > Windows. Yes, when you loaded a card specific driver, for them, and when they were on the same card, or on different PCI cards; _AND_ you _DID NOT_ share the same IRQ with an ISA device that was soldered onto the motherboard. It is highly probable that we are talking about an IRQ conflict, given that he _already stated_ that he was plugging a modem in, _AND_ that Windows rec0ognized it as COM4 without being beat over the head with a 2x4 or having a new driver loaded. Your post unnecessarily confused the issue. Realize that if the person were not a rank newby, he would have posted his question to -questions, where it belonged, instead of to -chat. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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