If I_HINT_IO or I_HINT_SYSTEM or I_HINT_DONTCARE is specified, then
DMA (I_HINT_USEDMA) with be used. The I_HINT_IO is intended for best
transfer performance and I_HINT_SYSTEM for most system performance
executing other applications. The fact is that both qualities are delivered best
when DMA is used.
However, there is a difference between above three modes and
I_HINT_USEDMA. It is possible for PCI bus DMA transfer to fail due to
hardware or OS instabilities. If this happens, The three modes described in this
paragraph will switch from that moment to interrupt mode (I_HINT_USEINTR)
until the computer is rebooted. An explicit
ihint()
call with I_HINT_USEDMA will
always use DMA; and, if a DMA bus error occurs, the iread or iwrite will return
with an error.
However, the PCI bus DMA error is very unlikely to occur.
TAMS 61622 PCTL delay.
The TAMS 61622 is much more flexible than any other available GPIO interface.
With the HP 2074/5 interface a user has a choice of one of eight delay time
values. The gaps between those values are significant and prevent performance
optimization. The TAMS 61622 accepts values directly in nanoseconds. The
range extends from 90 nanoseconds to 245000 nanoseconds (245
microseconds) allowing optimal transfer performance according to the length of
cable used. In addition, the time specified is applied with accuracy at any mode
of transfer, while other available GPIO interfaces add as much as 500 ns when
different modes are used. This caused users to configure more PCTL time than
actually required in order to compensate for worst possible transfer mode cases.
The TAMS 61622 PCTL delay is configurable by running the iocfg32.exe utility
(Windows), or it may be changed at any time from within an application by a call
to
igpioctrl(id, I_GPIO_PCTL_DELAY,
<val>)
where
<val>
could be
one of eight HP 2074/5 compatible values, or directly a value in nanoseconds
between 90 and 245000 inclusive.
The eight (0-7) of HP 2074/5 compatible values are interpreted as follows:
0 - 200ns, 1 - 400ns, 2 - 700ns, 3 - 1.2us, 4 - 2us, 5 - 5us, 6 - 10us, 7 - 50us.
Booting after configuring is not required with TAMS 61622.
When TAMS 61622 PCI GPIO card is configured via the SICL configuration it
does not require rebooting to take effect. Always choose Cancel or No button
when prompted to reboot the machine.
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