Agilent Technologies Agilent 82350B - Manual (Page 34)

1 Installing and Configuring the 82350B
22 82350B Installation and Configuration Guide
Some additional factors to consider are:
• The settings discussed above are per session. This means
you can open multiple sessions to a device and set different
transfer modes for different sessions. The actual mode used
will then depend on which session you are using for the
read/write calls.
• In both SICL (with hint = I_HINT_DONTCARE) and VISA
(with VI_ATTR_DMA_ALLOW_EN = VI_TRUE), the size of
the read request (as specified by bufsize in a SICL iread() or
count in a VISA viRead() function call) will determine the
mode used even if the number of bytes actually read is less.
• The default formatted IO read buffer size is 4096 so when
using this default size, formatted reads in SICL
(with hint = I_HINT_DONTCARE) and VISA (with
VI_ATTR_DMA_ALLOW_EN = VI_TRUE) will use Interrupt
mode even when a small number of bytes are expected.
• The default formatted IO write buffer size is 128 so when
using this default size, formatted writes in SICL
(with hint = I_HINT_DONTCARE) and VISA (with
VI_ATTR_DMA_ALLOW_EN = VI_TRUE) will use Polling
mode even sending a large number of bytes.
• In SICL, Polling mode will always be used for the iread(),
ifread(), and iscanf() regardless of the above settings, when
a termchr is set (itermchr() is not set to –1.
• In VISA, Polling mode will always be used for viRead(),
viBufRead(), and viScanf() regardless of the above settings,
when VI_ATTR_TERM_CHAR_EN = VI_TRUE.
The crossover point at which the Interrupt mode becomes
faster then the Polling mode depends on the CPU speed, with a
faster CPU having a higher crossover point.