Differences

This shows you the differences between two versions of the page.

--- resources:tools-software:linux-software:libiio_tips_tricks [20 Aug 2021 09:42] – created Michael Hennerich
+++ resources:tools-software:linux-software:libiio_tips_tricks [20 Aug 2021 10:30] – [Linux Contiguous Memory Allocator (or CMA)] Michael Hennerich
@@ Line 9: / Line 9: @@
 <note tip>Increase **iio_context_set_timeout()** timeout parameter or set to 0 to disables the timeout</note>
+===== Buffer handling, sizes and counts =====
+Typically set to a frame or chunk size suitable for signal processing (e.g. N x FFT_size)
+  * Small buffers -> less latency but more overhead
+  * Large buffers -> less overhead but more latency
+{{ :resources:tools-software:linux-software:libiio:internals:libiio_highspeed_interface.png?400 |}}
+<note tip>**Number of discrete buffers are configurable, default is 4.**\\
+Can change this using //**iio_device_set_kernel_buffers_count()**//</note>
+<note tip>**Capturing starts as soon as the buffer is created!**\\ //iio_device_create_buffer()//</note>
+<note tip>**FIFO like behavior new data is dropped in case it's not consumed fast enough!**</note>
+==== IIO buffer DMA max block size ====
+Max buffer size is limited by the max_block_size parameter
+  * Default 16M
+  * Can be adjusted
+There are two ways to adjust the max block size
+=== sysfs ===
+Set via **/sys/module/industrialio_buffer_dma/parameters/max_block_size** in bytes
+<WRAP box bggreen><wrap info>This specifies any shell prompt running on the target</wrap>
+<xterm>
+root@analog:~# **echo 67108864 > /sys/module/industrialio_buffer_dma/parameters/max_block_size**
+root@analog:~# **cat /sys/module/industrialio_buffer_dma/parameters/max_block_size**
+67108864
+root@analog:~#
+</xterm></WRAP>
+=== Kernel command line ===
+Append the following to your kernel command line
+  * **industrialio_buffer_dma.max_block_size=size_in_bytes**
+==== Linux Contiguous Memory Allocator (or CMA) ====
+  * Allocation of big, physically-contiguous memory blocks
+  * Reserve memory early at boot time
+  * Kconfig menu "Device Drivers" -> "Generic Driver Options"-> "Contiguous Memory Allocator"
+  * Kernel command line option cma=size_in_bytes
+  * PlutoSDR default 256M
+<note tip>Depending on your **IIO buffer DMA max block size** and **number of kernel buffer count** you may need to **CMA size**</note>
+===== Capturing large contiguous buffers =====
+Set kernel buffer count to 1

Wiki

Analog Devices Wiki

Differences

Analog Devices Wiki

Differences

Page Tools