I am currently working on a custom hardware which has SH_MOBILE architecture. Hardware comes with USB(peripheral) and a DMAC having 2 channels.
I am using R8a66597 UDC driver which is available in mainline kernel. I have added DMA related functions to the peripheral controller driver. Currently I am able to get the DMA working in TX path. But in RX path I am not able to use DMA, instead PIO is getting used. This is because the buffer address (buf in struct usb_request) is not 8 bit aligned.
I would want to know how to ensure that these data transfer buffer is DMA able?
Thanks in advance,
Srinidhi KV
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I am having a project that design a RISC V processor on DE10 kit and I've already created Verilog files for processor.
Because the processor has 32 bits data bus but the available external SDRAM has only 16 bits data, so how to connect them together?
DE10 Standard is a Cyclone V SoC, and SDRAM is controlled by the ARM HPS, you don't need to talk to it directly. The easiest way is to talk via Avalon bus (can be up to 128bit wide). You'll need to enable a port with a U-Boot script, see an example here
HPS clock frequency is higher than what you can get in your logic, so a 128bit bus is still an efficient way to talk to a DDR.
Now, you'll need to connect your 32 bit data bus to a wider data bus, not a more narrow one. For reading, you should be using a cache anyway, with a line width a multiple of 128bits.
I'm a beginner in the embedded system development world.
I would like some clarifications on the following questions.
Is every pin of a microcontroller (from here after referred to as mc) associated with a register?
Is it an one to one relationship?
How are ports (or groups of pins) assigned inside the mc?
Is it only possible to set a single pin low or high only?
No. Some pins are not associated with a register at all, e.g. Vcc and GND and if they do not have a dual use as a GPIO it also applies to clock/oscillator and reset pins.
If a pin is associated with registers, it is usually associated with several ones: one for determing the IO direction, one for reading the input, one or more for setting the output. For I2C, SPI, UART pins, the associated is indirect, i.e. the register mainly control the I2C/SPI/UART controller, which in turn is associated with the pin.
I don't understand the question
A GPIO pin can be set as input, as output in high state (delivering current or with a weak pull-up), as output in low state (sourcing current or with a weak pull-down) or in open-drain state (often similar to input mode). A pin can also be configured to be used by one fo the I2C/SPI/UART controllers or as DAC (outputting a variable voltage between GND and Vcc).
In addition to fundamental stuff like supply and clock pins, a MCU got numerous hardware peripherals internally. A hardware peripheral being something like a piece of GPIO (general-purpose input/output), ADC, UART, SPI etc. Each such hardware peripheral has a number of possible pins to which its functions can be routed.
Traditionally, these were pretty much fixed - if you wanted UART Tx then you would always get it on some fixed pin number, take it or leave it. Nowadays, most MCUs are quite flexible internally, allowing you to re-route hardware peripheral functionality to almost any pin you like, variably.
In either case, several hardware peripherals could share the same pin, and then it is MCU specific which one that takes precedence. For example GPIO could be present on the pin by default, but if you enable UART then maybe the MCU states that you get UART Tx on that pin instead.
As for the hardware peripheral called GPIO, they are almost always grouped in ports, where each port consists of a number of pins. Most often, port registers are either 8 bits or the size of the CPU's word length. Each bit in the various port registers corresponds to a pin.
You'll have a port data register, which is the actual read/write to the pin, a data direction register stating input or output, and then various other registers for interrupts, pull resistor enable etc etc.
Not all pins but all IOs (Input/Output) have a specific register.
Each IO has a specific group of registers. Bu also some registers may include specific bits which effects an IO or all IOs.
It depends of design of micro controller.
Yes it is.
I strongly recommend you to read some embedded hardware/software books(for example Newness Know It All books for embedded systems) and datasheets.
I've been given the task of getting ADC samples onto an embedded linux computer at the highest rate I can (up to about 300kSPS). I am playing with several different platforms (odroid, edison) but easrly on I realized the limitations of using the build in ADCs from within linux and timing (I am relativly new to this).
Right now I am reliably getting 150kSPS using a teensy 3.2 with a very basic swapping buffer, a PDB, and the USB connection. USB writes take 2.5usec no matter my buffer size so any faster and the ADC read interrupt collides with the USB and I get nothing.
My question is: Would using an external ADC chip enable faster speeds? I see chips on Digikey and Mouser advertising 600kSPS and higher with SPI and even parallel outputs... but I fell like the bottleneck is the teensy with USB writes. Even if it could (and I am sure it could) read values 600k times a second how do you get it onto the computer without falling behind?
also, it is for long term collection so I can't just store everything and write it once the collection is over. The edison has a built in microcontroller, but no SPI implemented yet.
Edit:
To clarify, my question is weather there is any way to get large amounts of data very fast into my embedded linux device programmatically or is there some layer between a fast SPI device and the comptuer that I don't know about. So far my mentors have suggested I 1) learn to write a device driver for the SPI device or 2) recompile an image with RT_PREEMPT.
I am trying to use DMA for my UART Rx and Tx. Till now I had the freeRTOS version of the serial demo working fine. It still works fine. However, now I have incorporated the UART DMA example, from the example projects.
the code is conditionally compiled, so that when a switch _HAS_DMA == 1, only then the DMA engine is configured, ram buffers are configured, and default UART ISRs as required by the FreeRTOS demo are removed.
At this point, whenever I send a serial byte stream, the running project simply gets reset.
I am using MPLAB IDE 8.92, XC16 v1.20, Explorer-16 platform, dspic33fj256gp710 part.
The DMA code included does not use any FreeRTOS API calls.
I have setup the project so that StackOverflow is detected using the FreeRTOS configuration option. But the code does not reach the Stackoverflow hook function. I have also included the U2ErrInterrupt ISR to see if incoming bytes are coming in fine, however even that interrupt is not reached.
Has any one faced this before?
interestingly, the UART DMA Loopback example from Microchip website, which uses the MPLAB C30 compiler, works fine on my board.
any pointers on this one? I could not locate any code examples in the FreeRTOS forum on how to use the DMA for UART, but it is suggested to use this method in production code for efficiency.
Need help here.
Thanks and best regards,
Vishal
OK. I found the culprit. Its me. :)).
When setting up the DMA to receive UART interrupts, one should not enable UART interrupt separately in software. Which is what I was doing. In addition, I had conditionally un-compiled the UART ISRs from my code !!!. So in effect, whenever a byte was received by the UART engine, the processor is getting confused as to who will serve this interrupt, DMA or Application code. I thing the PC would point to the designated UART RX ISR vector location, where the processor would not find anything, and this was causing the reset. Or may be there was a race condition setup between the DMA and the processor to serve this interrupt, which was causing the reset.
Now that I have setup UART so that Interrupts are not enabled separately by application, when DMA is going to serve the UART RX, my code is working fine. I am yet to integrate the whole thing with FreeRTOS deferred interrupt processing using binary semaphores, but I hope I will not see any troubles there.
There is not much documented about this though...neither in Microchip manuals nor in the FreeRTOS examples.
Also, I found that when using DMA with UART, as per the manual, the DMA receives WORDS from the UART RX engine, with lower byte having the data, and upper byte having the status. If the DMA is also used for UART Tx, and is set to transfer WORDS to UART TXREG, the two intelligently manage to send only the lower data byte out. So the receiving party still gets expected bytes. This is also not documented well.
I will try to post my code here for future generations though :)).
I'm doing a USB device is to control stepper motors. I've done this before using a parallel port. because these ports do not exist in current motherboards, I decided to implement a USB communication between my device and the PC (host).
To achieve My objective, I endowed the freescale microcontroller the device with that has a USB module 12Mbps.
My USB device must receive 4 bytes (one for each motor driver) at a given time, because every byte is a step that should move the engine.
In the PC (Host) an application of user processes a text file with information and make the trajectory coordinates sending bytes at a certain rate for each motor (time is trivial to achieve the acceleration and speed of the motors) .
Using the parallel port was an easy the task because each byte is sent sequentially to a time determined by the user app.
doing a little research about full speed USB protocol understood that the frame is sent every 1ms.
then you can send 4 byte or many more every 1ms but I can not manage time like I did with the parallel port.
My microcontroller can send up to 64 bytes per frame (Based on transfer papers type Control, Bulk, Int, Iso ..).
question 1:
I want to know in what way I can send 4-byte packets faster than every 1 ms?
question 2:
What type of transfer can advise me for these type of devices?
Thanks.
Like Ricardo said, USB-serial will suffice.
As for the type of transfer, try implementing a CDC stack and use your SCI receiver to listen for PC commands. That will give you a receive buffer which will meet your needs.
Initialize your SCI (baud, etc)
Enable receiver and interrupt
On data receive, move it to your 4-byte command buffer
Clear receive buffer, wait for more
When you have all 4 bytes, fire off the steppers! Four bytes should take µs.
Check with Freescale to see if your processor is supported.
http://cache.freescale.com/files/microcontrollers/doc/support_info/USB_STACK_RELEASE_NOTES_V4.1.1.pdf?fpsp=1
There might even be some sample code to get you started.
-Cheers
I am achieving the same goal (driving/control CNC machines) like this:
the USB device is just synchronous I/O parallel port. Using continuous bulk transfer one pipe as input and one as output. This way I was able to achieve synchronous 64bit parallel communication with ~70KHz sample rate. It uses traffic around (i)4.27+(o)4.27 MBit/s that is limit for mine MCU and code. Bigger speeds cause jitter on the output due to USB events interrupts.
How to do it (on MCU side)
I have 2 FIFO's one for ingoing and one for outgoing data. I have timer interrupt occurring with sample rate frequency. In it I read the inputs and feed it to the first FIFO and read data from the other FIFO and send it to the outputs.
On top of that the USB task is called (inside the same interrupt) checking FIFO for sending to and incoming data from USB handling the transfer itself
I choose ATMEL AT32UC3A chips for this task. After a long and pain full research I decided these MCU's because they have enough memory for both FIFO's and program so no need for additional IC. It has FPGA package which can be used (BGA is not an option). It has HS USB (most USB MCU's have only FS like yours). It runs at 66MHz. It supports many interesting features (did interesting projects with it in the past) and of coarse I have experience with ATMEL MCU's from past
So if you want to achieve something similar then
start with bulk transfer (PC -> USB -> MCU -> output)
add FIFO if needed
do not know the sample rate you need. The old LPT's could handle from 80-196KHz depend on the manufactor. The modern ones are much much slower (which is silly and sad).
measure the critical sample rate
you need oscilloscope or very good hearing for this. The output data must be synchronous so no holes in it, no jitter, etc...
if any of these are present you have to lower the sample rate. Mine setup could handle even 1MHz sample rate but the USB jitter was present (sometimes USB event froze the sending for longer that one sample...) so I achieve only 70KHz of stable output.
if needed also inputs then add them
but only if the output is working as it should. Do not forget to lower the sample rate after this too ... Use separate bulk pipes and FIFOs for input and output.