Date: Tue, 13 Aug 2002 06:33:40 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Maksim Yevmenkin <myevmenk@exodus.net> Cc: "M. Warner Losh" <imp@bsdimp.com>, <current@FreeBSD.ORG> Subject: Re: Interrupt vs. polling on -current Message-ID: <20020813062053.O26164-100000@gamplex.bde.org> In-Reply-To: <3D57EEA5.96D397CC@exodus.net>
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On Mon, 12 Aug 2002, Maksim Yevmenkin wrote: > Xircom card is a Bluetooth card with UART interface. Bluetooth link > speed is about 700KB/s. I do not think that standard 16550A UART with > 16 bytes FIFO can handle such speed. I also can not believe that Xircom > would sell such low speed Bluetooth card (115200 bit/s). I think that > Xircom card must have a much bigger FIFO in order to handle full speed. > W2K, for example, has special driver for Xircom card. Big fifos for dumb hardware can also cause by problems by taking a long time to drain, thus increasing latency for other devices. "dumb hardware" here means almost anything that must be accessed in PIO mode. One of the main reasons why sio uses a fast interrupt handler was that such hardware was common 10-15 years ago (for pre-DMA IDE disks). In Linux the disk driver (sort of) used a fast interrupt handler too, and competition between these handlers caused many silo overflows. Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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