Hi there,
My problem is I need to drive a VGA monitor with a PSoC6. My solution is to use DMA transfers from an image buffer to a GPIO Port. The GPIO ...
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Hi there,
My problem is I need to drive a VGA monitor with a PSoC6. My solution is to use DMA transfers from an image buffer to a GPIO Port. The GPIO Port is connected to an external high speed DAC to convert the digital 8 bit signal into an analog signal for the monitor.
I've achieved this reasonably well with my PSoC5 LP, PSoC Creator, and the UDB Control Register. The PSoC5 LP would DMA transfer byte-by-byte to the control register block, and this block would be connected in the schematic editor to a bunch of GPIO pins. The pins would update their state at a fixed frequency and according to the value of the incoming DMA byte. This worked very fast and without problems.
However, I've now switched to the PSoC6 MCU, specifically I have the CY8CPROTO-062-4343W (2MB Flash). This board is not supported in PSoC Creator as far as I can tell (I have no idea why, but it is what it is). Since I'm now using Modus Toolbox, I can't create the UDB Control Register I did with the PSOC5. Instead, I looked at the TRM manual and found out you can directly write to the memory mapped GPIO Ports and update their state that way.
I figured out this is how to get the address of the port:
uint32_t* port9 = (uint32_t*) Cy_GPIO_PortToAddr(9);
and you can write an arbitrary byte to it like:
*port9 = 0xff;
After figuring this out I was relieved, because I thought I could now just do the same thing: set-up a continuous byte-to-word DMA transfer from my source buffer to this peripheral address. I looked at DMA examples for PSoC6 and managed to get it working. Here are some relevant snippets:
// Configure descriptor source. Buffer_a = framebuffer to read from.
Cy_DMAC_Descriptor_SetSrcAddress(&RDMA_Descriptor_0, (uint32_t *) buffer_a);
Cy_DMAC_Descriptor_SetDstAddress(&RDMA_Descriptor_0, (uint32_t *) port9);
// Standard Channel Config
Cy_DMAC_Channel_SetDescriptor(RDMA_HW, RDMA_CHANNEL, &RDMA_Descriptor_0);
Cy_DMAC_Channel_SetInterruptMask(RDMA_HW, RDMA_CHANNEL, CY_DMAC_INTR_MASK);
Cy_DMAC_Channel_Enable(RDMA_HW, RDMA_CHANNEL);
// Start DMA listen for signal
Cy_DMAC_Enable(RDMA_HW);
RDMA is what I named my DMAC channel 0. See the attached image for the exact configuration.
I was very happy because it seemed to work fine. But under closer inspection I realized a huge problem. The generated signal was not consistent.
The source buffer looks like this: All zeros with three consecutive 1's. It gets initialized at the start of main, and never edited again.
for (int i = 0; i < 640; i++) buffer_a[i] = 0x00;
buffer_a[200] = 0xff;
buffer_a[201] = 0xff;
buffer_a[202] = 0xff;
Thus, on my oscilloscope I'm expecting to see a bunch of zeros followed by a 3 pixel bump.
Like: ______---_______ (see correct_square.jpg)
However, I'm not getting this always. Sometimes, almost every other time, the bump is messed up. Sometimes there's a pixel missing
Like: _______-_-_______ or _______--_______ (See corrupt_square.jpg and half_square.jpg)
And other times there's just a weird, very short dip.
Like: _______-.-________ (See corrupt_square2.jpg).
Also note that I'm running the peripheral clock at 100Mhz. If I divide it by 4 (run it at 25Mhz), I don't have these problems but anything >25Mhz creates this inconsistent behavior. Dividing it by 4 is not an option for me though, as that GPIO update speed is way too slow (the PSOC5 even could clock at 74Mhz without problems).
I'm at a loss of what to do. Is this a limitation of the PSoC6? Surely not? Is there a better / fast / more reliable way to update GPIO pins as quickly as possible instead of writing directly to the Register Port Address? Could I somehow use UDB like I did with the PSoC5?
What can I do?
Any advice would be greatly appreciated. It's very hard to find resources on this topic IMO, so I'm hoping someone can shed some light onto this 🙂
Thank you!
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