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authorDavid S. Miller <davem@davemloft.net>2008-04-17 23:56:30 -0700
committerDavid S. Miller <davem@davemloft.net>2008-04-17 23:56:30 -0700
commit1e42198609d73ed1a9adcba2af275c24c2678420 (patch)
tree32fd4d9073bfc0f3909af8f9fb4bcff38951d01a /Documentation/spi/spi-summary
parent794eb6bf20ebf992c040ea831cd3a9c64b0c1f7a (diff)
parent4b119e21d0c66c22e8ca03df05d9de623d0eb50f (diff)
Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/torvalds/linux-2.6
Diffstat (limited to 'Documentation/spi/spi-summary')
-rw-r--r--Documentation/spi/spi-summary15
1 files changed, 14 insertions, 1 deletions
diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary
index 8861e47e5a2..6d5f18143c5 100644
--- a/Documentation/spi/spi-summary
+++ b/Documentation/spi/spi-summary
@@ -116,6 +116,13 @@ low order bit. So when a chip's timing diagram shows the clock
starting low (CPOL=0) and data stabilized for sampling during the
trailing clock edge (CPHA=1), that's SPI mode 1.
+Note that the clock mode is relevant as soon as the chipselect goes
+active. So the master must set the clock to inactive before selecting
+a slave, and the slave can tell the chosen polarity by sampling the
+clock level when its select line goes active. That's why many devices
+support for example both modes 0 and 3: they don't care about polarity,
+and alway clock data in/out on rising clock edges.
+
How do these driver programming interfaces work?
------------------------------------------------
@@ -379,8 +386,14 @@ any more such messages.
+ when bidirectional reads and writes start ... by how its
sequence of spi_transfer requests is arranged;
+ + which I/O buffers are used ... each spi_transfer wraps a
+ buffer for each transfer direction, supporting full duplex
+ (two pointers, maybe the same one in both cases) and half
+ duplex (one pointer is NULL) transfers;
+
+ optionally defining short delays after transfers ... using
- the spi_transfer.delay_usecs setting;
+ the spi_transfer.delay_usecs setting (this delay can be the
+ only protocol effect, if the buffer length is zero);
+ whether the chipselect becomes inactive after a transfer and
any delay ... by using the spi_transfer.cs_change flag;