Hello!
I have a AM335x (a phycore module, to be specific) I'm using to record some serial messages. I'd like to use Rx DMA, and I was hoping you could tell me how best to activate it.
I believe I have the 8250 driver configured correctly to enable DMA:
root@testboard:~# zcat /proc/config.gz | grep -i 8250 CONFIG_SERIAL_8250=y CONFIG_SERIAL_8250_DEPRECATED_OPTIONS=y CONFIG_SERIAL_8250_CONSOLE=y CONFIG_SERIAL_8250_DMA=y CONFIG_SERIAL_8250_PCI=y CONFIG_SERIAL_8250_NR_UARTS=10 CONFIG_SERIAL_8250_RUNTIME_UARTS=10 # CONFIG_SERIAL_8250_EXTENDED is not set CONFIG_SERIAL_8250_FSL=y # CONFIG_SERIAL_8250_DW is not set # CONFIG_SERIAL_8250_EM is not set # CONFIG_SERIAL_8250_RT288X is not set CONFIG_SERIAL_8250_OMAP=y CONFIG_SERIAL_8250_OMAP_TTYO_FIXUP=y # CONFIG_SERIAL_8250_INGENIC is not set # CONFIG_SERIAL_8250_MID is not set # Non-8250 serial port support # CONFIG_DEBUG_UART_8250 is not set
My questions are:
1. What do I need to do in my application to ensure Rx DMA is activated? Is DMA used for all reads, even those that can return after a single byte? Do I get DMA when I set c_cc[VMIN] and do a blocking read with a timeout? Can I get DMA when I read with a select? I've read some program examples, but none of them are specific about DMA.
2. I'm pretty new to this so I want to check my work to make sure I haven't messed something up. Is there a way I can verify that DMA is active and working?
3. Can I choose the size of the DMA buffer, and if so how? As I'm just logging data I don't need to access it in real time, but I'd like a big DMA buffer so nothing gets dropped even if the processor stalls for whatever reason.
Thanks for your help!
