Lava LavaPort 650, Installation Manual

The LavaPort-650 uses a 16650 UART incorporating a 32-byte FIFO (first-
in first-out) buffer.

The FIFO control tabs set the buffer “trigger” levels. When the buffer is
filled to its trigger level with the selected number of bytes, the CPU will
be interrupted and asked to either reload the buffer (for transmission),
or retrieve data from the buffer (for reception).

Most efficient data transmission occurs when the CPU is interrupted
infrequently. For each interrupt, the CPU can then service the buffer with
larger data blocks: during transmission, it can place a large burst of data
into the buffer, and during reception it can retrieve a large block from
the buffer and then continue multi-tasking.

Ideally therefore, Receive triggers should be set as high as possible and
Transmit triggers as low as possible.

However, if the Transmit trigger levels are set too low, or Receive triggers
too high, and the CPU is busy when an interrupt is called by the
LavaPort, a short period of inactivity may occur between the port and
the modem. This will reduce effective transmission/reception speeds.

Optimum buffer settings are dependent on your modem speed, your
CPU speed, and the amount of multi-tasking that occurs while online.
For a fast modem and fast CPU performing few multi-tasking functions,
set transmit triggers low and receive triggers high. If multi-tasking while
online, set transmit triggers higher and receive triggers lower.

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