UART uDMA transfer problems - first byte repeated and maximum ~32 bytes transferred

Tom Oldbury

Other Parts Discussed in Thread: TM4C123GH6PM

Hi all,

I'm trying to use uDMA to control UART6 data transmit and receive. Eventually, I plan to use UART4 as well in the same manner.

UART6 is configured as 115200 8N1 standard UART and I want to use the uDMA to transfer up to 128 bytes at a time without processor intervention.

I am using a TM4C123GH6PM on custom hardware.

This currently seems to initiate a transfer but the first byte is repeated 32 times, and sizes above 32 bytes just seem to be "clipped" so to speak. No bytes beyond 32 are ever transferred (I do not see start or stop bits in the UART waveform.)

Here is my code, some of which is based off the working example (udma_demo)

uint8_t test_data[128];
uint32_t testn = 0;

/**
 * Prepare the UART and DMA peripherals for fast transmit mode.
 *
 * The UART modules will be configured for the correct baud rate.
 */
void init_uart_dma()
{
	SysCtlPeripheralEnable(SYSCTL_PERIPH_UDMA);
	SysCtlPeripheralEnable(SYSCTL_PERIPH_UART6);
	uDMAEnable();
	uDMAControlBaseSet(udma_controltbl);
	UARTConfigSetExpClk(UART6_BASE, SysCtlClockGet(), 115200, (UART_CONFIG_WLEN_8 | UART_CONFIG_STOP_ONE | UART_CONFIG_PAR_NONE));
	UARTFIFOLevelSet(UART6_BASE, UART_FIFO_TX4_8, UART_FIFO_RX4_8);
	UARTEnable(UART6_BASE);
	UARTDMAEnable(UART6_BASE, UART_DMA_RX | UART_DMA_TX);
	uDMAChannelAssign(UDMA_CH11_UART6TX);
	uDMAChannelAttributeDisable(UDMA_CH11_UART6TX, UDMA_ATTR_ALTSELECT | UDMA_ATTR_USEBURST | UDMA_ATTR_HIGH_PRIORITY | UDMA_ATTR_REQMASK);
	uDMAChannelAttributeEnable(UDMA_CH11_UART6TX, UDMA_ATTR_USEBURST);
	uDMAChannelControlSet(UDMA_CH11_UART6TX, UDMA_SIZE_8 | UDMA_SRC_INC_8 | UDMA_DST_INC_NONE | UDMA_ARB_4);
	GPIOPinTypeUART(GPIO_PORTD_BASE, GPIO_PIN_4 | GPIO_PIN_5);
	GPIOPinConfigure(GPIO_PD4_U6RX);
	GPIOPinConfigure(GPIO_PD5_U6TX);
	DBG_PRINTF("uDMA for UART initialised\r\n", 0);
}

/**
 * Transfer data over UART TX via uDMA.
 *
 * A maximum of 1023 bytes can be transferred in a single packet.
 *
 * Blocks while relevant uDMA transfer is in use.
 *
 * @param		port			UART_CH_BLE or UART_CH_RASPI
 * @param		nbytes		number of bytes to transfer (0-1023)
 * @param		data			pointer to data structure to read from
 */
void uart_dma_tx(uint32_t port, uint32_t nbytes, uint8_t *data)
{
	strcpy(test_data, "TestDataPacket");
	test_data[0] = testn;
	// wait for uDMA channel to be free
	while(uDMAChannelIsEnabled(UDMA_CH11_UART6TX));
	uDMAChannelTransferSet(UDMA_CH11_UART6TX, UDMA_MODE_BASIC, &test_data, (void *)(UART6_BASE + UART_O_DR), testn);
	uDMAChannelEnable(UDMA_CH11_UART6TX);
	testn++;
	testn %= 64;
}

Thanks for any help that can be offered

Oscilloscope screenshot showing repeated byte:

Waveform showing maximum packet size and lack of any transfer past 32 bytes or so:

over 9 years ago

0 Amit Ashara over 9 years ago

TI__Guru**** 244440 points

Hello Tom

How has the DMA Table "udma_controltbl" intialized and why is the size of transfer set as "0", as per the code above?

Regards
Amit

0 Tom Oldbury over 9 years ago in reply to Amit Ashara

Intellectual 540 points

Hello Amit,

Here is the initialisation of the DMA control table:

#pragma DATA_ALIGN(udma_controltbl, 1024)
uint8_t udma_controltbl[1024] __attribute__ ((aligned(1024)));

The transfer size starts at zero and counts up. I did this to see the exact number of bytes that I could transmit, which works out to around 32 bytes.

Thanks,

0 Amit Ashara over 9 years ago in reply to Tom Oldbury

TI__Guru**** 244440 points

Hello Tom

The transfer size programmed to the DMA control table counts down in the DMA. it must be a non-zero value.

Regards
Amit

0 Tom Oldbury over 9 years ago in reply to Amit Ashara

Intellectual 540 points

Hello Amit,

`testn' sets the size of the transfer. This value starts at zero and counts to 63 before resetting to zero. This is just part of a test to see how much data the DMA would transfer.

I have tried fixing the size of the transfer to 32 bytes or 48 bytes, and the same problem occurs with a fixed ~32 byte limit and no subsequent bytes are transmitted, as well as the repeated byte issue.

Thanks,

0 Amit Ashara over 9 years ago in reply to Tom Oldbury

TI__Guru**** 244440 points

Hello Tom,

Can you zip your project and attach it to the forum post so that I can try to reproduce the issue on a LaunchPad

Regards
Amit

0 Tom Oldbury over 9 years ago in reply to Amit Ashara

Intellectual 540 points

Hello Amit,

Thanks for your help. I discovered I had a stack corruption bug (or memory corruption of similar nature) which may have caused this issue. After resolving this the problem has gone away and the DMA works correctly. The code above is unchanged and appears to work properly now. Whilst I cannot be certain this was causing the problem it seems likely. I will update if I have further issues.

Thanks again,

0 Amit Ashara over 9 years ago in reply to Tom Oldbury

TI__Guru**** 244440 points

Hello Tom

What is the stack and heap size set in the linker?

Regards
Amit

0 Tom Oldbury over 9 years ago in reply to Amit Ashara

Intellectual 540 points

Originally 2KB for stack, no heap. I am using printf with quite a few arguments which may be causing stack overflows.

0 Amit Ashara over 9 years ago in reply to Tom Oldbury

TI__Guru**** 244440 points

Hello Tom,

Thanks. printf does take stack but with 2KB it should be a memory leak also. My fear is that after increasing the stack it may stop working after some more time of testing.

Regards
Amit

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UART uDMA transfer problems - first byte repeated and maximum ~32 bytes transferred