Moreover, three independent enable bits are available to enable IRQ on half transfer, full transfer and transfer error. Separate interrupt enable bits are available for flexibility. But, it also provides a general and more user-friendly way to configure the peripheral, without forcing the programmers to now how to configure its registers in detail. Please refer to Reference manual for connection between peripherals and DMA requests.
In this case the DMA interrupt is configured. Using const modifier to put variable in to the Flash Memory by Linker. Read more here. To measure the execution time in a logic analyzer, output a pulse on PC9 during the transfers. Here are the output pulses showing that memcpy needs us to complete while DMA only needs us. By default, these callbacks are not set, therefore, write 2 functions to handle DMA interrupts.
The DMA interrupt indicates time execution of the 2 nd half transfer. Using Word-aligned memory block to speed up the DMA transfer. Note that transfer size will be reduced.
As seen in below image, the DMA transferring time in Word-aligned mode is only us, comparing the us in Byte-aligned mode. Using World-aligned to reduce DMA transfer time. Skip to content.
This means that after any PMP transfers is completed an interrupt will be generated. We do not need to write the Interrupt Service Routine ISR for this, it's all handled internally and the DMA module will intercept the interrupt and clear the interrupt flag for us each time.
Next, we can see that each DMA channel has a priority , just like interrupts did. This priority is also important in DMA chaining. A word on interrupts. First, why have I changed to using the Shadow Register Set instead of the software interrupts? Simply put, it's faster because it means the PIC32 doesn't have to save the contents of all the many registers to memory before it calls the interrupt service routine ISR. When the DMA transfer is done, it can generate an interrupt to let us know it's done.
Knowing what we know about ISRs and how they take valuable time, you may be tempted to do this:. However, this would be a big mistake. In the DMA datasheet in a code example they say: " continuously polling the DMA controller in a tight loop would affect the performance of the DMA transfer " You could check the flag, wait a few microseconds and check again but I prefer to use the interrupt approach as, in theory, it could result in better turn-around times.
There are 8 different kinds of interrupts that can be generated which makes the DMA module very flexible. Can't we do something to shorten that horrendous ISR declaration? Turns out yes, we can. All a matter of personal preference, really. This pattern can be either 8 or 16 bits. This is very useful in reading from SD cards, because before we read a block we have to output 0xFF until the SD card returns the 0xFE token to tell us it's ready to give us the data. You can set up a pattern match like this:.
Right, that's long enough for one day. Categories: pic Tags: code , DMA. As per my example, I'd do this: while! How to install Windows 7 Professional operating system in your home desktop or laptop Are you looking for installation guide of Windows 7 Professional operating system. Windows 7 is an operating system created by Microsoft to be installed on computers and laptops.
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