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Re: SPI driver
On Thu, 7 Feb 2019, Michael van Elst wrote:
I've written a userland interface to our spi(4) driver.
Neat. I'm interested in SPI, but pardon me if I am a bit ignorant. If you
don't have time to answer it's no problem.
crw------- 1 root wheel 346, 0 Jan 5 16:02 /dev/spi0
I assume there is no concept of a block-mode for SPI, directly. It's only
a transport like I2C or JTAG right? Don't SD cards use it for IO or
something related ?
SPI_IOCTL_CONFIGURE calls spi_configure() to chose operational mode and
I see the struct sets a clock in Hz. Is SPI always synchronous ? Can one
vary the clock frequency ? Is there a way to sense what the other side
will max out at ? How can one know the width of data-bits in a cycle or
does it not matter and you just set sendlen & recvlen and not worry about
The interface is different from spigen(4) used by FreeBSD and also
different from an early example of an SPI driver by Jonathan Kollasch.
Why didn't you just steal it? I'm kidding, but still a bit curious.
As there is no kind of session handling,
Is SPI meant to be stateful but the driver can't do it yet or is that just
how SPI works intrinsically ? Isn't it kinda low level bit-banging stuff
where you control which wire is doing what and who's on edge vs level
etc... ? So, you're saying "sessions" are just the responsibility of the
user/implementer, right ?
Thanks for your hard work, Michael.
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