Preface While writing a custom SDMA script for copying data arriving from an eCSPI peripheral into memory, it occurred to me that there is more than one way to fetch the data from the peripheral. This post summarizes my rather decisive finding in this matter. Spoiler: Linux’ driver could have done better (Freescale’s v4.1.15) I’ve [...]
Motivation Even though SPI is commonly used for controlling rather low-speed peripherals on an embedded system, it can also come handy for communicating data with an FPGA. When using the official Linux driver, the host can only be the SPI master. It means, among others, that transactions are initiated by the host: When the bursts [...]
I ran into a weird problem while attempting to enable SDMA for UARTs on an i.MX53 processor running Freescale’s 2.6.35.3 Linux kernel: To begin with, the UART would only transmit 48 bytes, which is probably a result of only one watermark event arriving (the initial kickoff filled the UART’s FIFO with 32 bytes, and then [...]
Since the device tree is the new way to set up hardware devices on embedded platforms, I hoped that I could avoid the “platform” API for picking which driver is going to take control over what. But it looks like the /arch/arm disaster is here to stay for a while, so I need to at [...]
What this blob is all about Running some home-cooked SDMA scripts on Freescale’s Linux 2.6.28 kernel on an i.MX25 processor, I’m puzzled by the fact, that cache flushing with dma_map_single(…, DMA_TO_DEVICE) doesn’t hurt, but nothing happens if the calls are removed. On the other hand, attempting to remove cache invalidation calls, as in dma_map_single(…, DMA_FROM_DEVICE) [...]
These are a couple of examples of SDMA assembly code, which performs data copy using the DMA functional unit. The first one shows how to copy data from application memory space to SDMA memory. The second example copies data from one application memory chunk to another, and hence works as an offload memcpy(). To actually [...]
This is part IV of a brief tutorial about the i.MX51′s SDMA core. The SDMA for other i.MX devices, e.g. i.MX25, i.MX53 and i.MX6 is exactly the same, with changes in the registers’ addresses and different chapters in the Reference Manual. This is by no means a replacement for reading the Reference Manual, but rather [...]
This is part III of a brief tutorial about the i.MX51′s SDMA core. The SDMA for other i.MX devices, e.g. i.MX25, i.MX53 and i.MX6 is exactly the same, with changes in the registers’ addresses and different chapters in the Reference Manual. This is by no means a replacement for reading the Reference Manual, but rather [...]
This is part II of a brief tutorial about the i.MX51′s SDMA core. The SDMA for other i.MX devices, e.g. i.MX25, i.MX53 and i.MX6 is exactly the same, with changes in the registers’ addresses and different chapters in the Reference Manual. This is by no means a replacement for reading the Reference Manual, but rather [...]
This is part I of a brief tutorial about the i.MX51′s SDMA core. The SDMA for other i.MX devices, e.g. i.MX25, i.MX53 and i.MX6 is exactly the same, with changes in the registers’ addresses and different chapters in the Reference Manual. Freescale’s Linux drivers for DMA also vary significantly across different kernel releases. It looks [...]