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Caribou-SMI API Driver

This directory contains a user-mode interface code with the bcm2835_smi kernel module. To start working with the interface, some kernel modules need to be probed first.

By default, CaribouLite boards are pre-programmed to automatically probe the SMI modules on startup. Each CaribouLite contains an EEPROM device that in programmed during production with the updated device tree overlay (for more info see here) file that loads on startup. This device tree "requests" loading the SMI associated kernel modules on startup. So if you have your CaribouLite board mounted on the 40-pin header, the module probing is not necessary.

To check whether these modules are probed, follow the next command in your Raspberry Pi terminal:

lsmod | grep smi

you should be seeing the following output:

bcm2835_smi_dev     16384   0
bcm2835_smi         20480   1   bcm2835_smi_dev

If you do not see these modules, please check:

  1. The CaribouLite is properly mounted and powered.
  2. The CAribouLite is properly flashed - follow this link

For detailed hardware-related information on the SMI interface, please click here

The API

Initializing and closing the SMI instance

Opening the device and configuring the error-callback-function to be triggered once an error ocurred:

int caribou_smi_init(caribou_smi_st* dev,
                    caribou_smi_error_callback error_cb,
                    void* context);

Closing the device:

int caribou_smi_close (caribou_smi_st* dev);

Reading and writing into the device

Reading into a buffer with timeout. If the SMI connected device (in this case, CaribouLite) doesn't have enough data to send, this function will wait till the timeout elapses. For non-blocking operation, please set timeout = 0

int caribou_smi_timeout_read(caribou_smi_st* dev,
                            caribou_smi_address_en source,
                            char* buffer,
                            int size_of_buf,
                            int timeout_num_millisec);

writing - TBD

Stream operations

In most cases, working with file read/write synchronously is not the right choice. If we want an asynchronous operation with events and callbacks, we should setup a stream as follows:

int caribou_smi_setup_stream(caribou_smi_st* dev,
                                caribou_smi_stream_type_en type,
                                caribou_smi_channel_en channel,
                                int batch_length, int num_buffers,
                                caribou_smi_data_callback cb,
                                void* serviced_context);

batch_length - is the length of a single buffer to serve (in bytes) num_buffers - is the number of batch buffers to allocate - for fluent buffer swapping cb - data callback function that is triggered every time a buffer is ready to be served. serviced_context - the data "requester" that is being serviced by the I/Q data. In most cases that is a higher layered driver / API. The returned integer is the stream ID used for further operations.

Notes: Once the stream is created it is operational but paused! to activate it use the following function (on the specific stream ID). This function is used also for pausing the stream (run = 0).

int caribou_smi_run_pause_stream (caribou_smi_st* dev, int id, int run);

Gracefully disposing the stream is done using the "destroy" function

int caribou_smi_destroy_stream(caribou_smi_st* dev, int id);