BSP Developer's Guide

4
Hardware Guidelines
4.4.2 System Clock
A system clock interrupt is mandatory. The system clock for VxWorks requires an
interrupt between 30 Hz and ~2 KHz.
The default is 60 Hz and it is desirable to generate this frequency exactly. Relying
on baud-rate generators often makes this precision unattainable.
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4.4.3 Auxiliary Clock
VxWorks uses an auxiliary clock from 30 Hz to ~2 KHz to profile CPU utilization.
This is required by the spy utility. It is useful to have a 24-bit (or greater) counter
driven at a high frequency (~10 MHz) for profiling performance.
4.4.4 Timestamp Clocks
Many of the generic timers in target/src/drv/timer include timestamp
functionality. A timestamp driver provides a high-resolution time measurement
facility, typically used by the WindView product. See the WindView User’s Guide:
Creating a VxWorks Timestamp Driver for more information on the API.
4.4.5 Serial Ports
VxWorks currently requires one RS-232 serial port, which is needed during the
development and debug phases. The device should be configurable to operate at a
number of “standard” baud rates; 9600 is preferred. Standard communications
parameters are 8 data bits, 1 stop bit, no parity, and no modem control lines. It is
possible to boot VxWorks without a serial interface, and in production, it is
conceivable that embedded systems will not have a serial interface.
The preference is to consider the target board to be DCE. Therefore, the RS-232
connectors should be one-to-one and not null-modem (pins 2 and 3 crossed). This
allows for a straightforward connection to a standard terminal.
VxWorks supports software flow control; hardware flow control signals are
usually ignored. Therefore, only three lines (transmit, receive, and signal ground)
are required for operation.
The API for SIO type serial drivers has been expanded to include support for
hardware flow control and for changing the operational parameters for each serial
device. The user can alter the hardware options flag for each device in order to
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