The
spigen
driver provides direct access to a slave device on the SPI bus.
Each instance of a
spigen
device is associated with a single chip-select
line on the bus, and all I/O performed through that instance is done
with that chip-select line asserted.
SPI data transfers are inherently bi-directional; there are no separate
read and write operations.
When commands and data are sent to a device, data also comes back from
the device, although in some cases the data may not be useful (or even
documented or predictable for some devices).
Likewise on a read operation, whatever data is in the buffer at the start
of the operation is sent to (and typically ignored by) the device, with each
outgoing byte then replaced in the buffer by the corresponding incoming byte.
Thus, all buffers passed to the transfer functions are both input and
output buffers.
The
spigen
driver provides access to the SPI slave device with the following
ioctl(2)
calls, defined in
<sys/spigenio.h>:
|
| SPIGENIOC_TRANSFER (struct spigen_transfer)
|
| |
Transfer a command and optional associated data to/from the device,
using the buffers described by the st_command and st_data fields in the
spigen_transfer.
Set
st_data.iov_len
to zero if there is no data associated with the command.
struct spigen_transfer {
struct iovec st_command;
struct iovec st_data;
};
|
| SPIGENIOC_TRANSFER_MMAPPED (spigen_transfer_mmapped)
|
| |
Transfer a command and optional associated data to/from the device.
The buffers for the transfer are a previously-mmap'd region.
The length of the command and data within that region are described by the
stm_command_length
and
stm_data_length
fields of
spigen_transfer_mmapped.
If
stm_data_length
is non-zero, the data appears in the memory region immediately
following the command (that is, at offset
stm_command_length
from the start of the mapped region).
struct spigen_transfer_mmapped {
size_t stm_command_length;
size_t stm_data_length;
};
|
| SPIGENIOC_GET_CLOCK_SPEED (uint32_t)
|
| |
Get the maximum clock speed (bus frequency in Hertz) to be used
when communicating with this slave device.
|
| SPIGENIOC_SET_CLOCK_SPEED (uint32_t)
|
| |
Set the maximum clock speed (bus frequency in Hertz) to be used
when communicating with this slave device.
The setting remains in effect for subsequent transfers; it
is not necessary to reset this before each transfer.
The actual bus frequency may be lower due to hardware limitations
of the SPI bus controller device.
|
| SPIGENIOC_GET_SPI_MODE (uint32_t)
|
| |
Get the SPI mode (clock polarity and phase) to be used
when communicating with this device.
|
| SPIGENIOC_SET_SPI_MODE (uint32_t)
|
| |
Set the SPI mode (clock polarity and phase) to be used
when communicating with this device.
The setting remains in effect for subsequent transfers; it
is not necessary to reset this before each transfer.
|
|
