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.


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