Variable packet data output using axi-uartlite (Ublox and Zedboard)

[gcp]

Dear FPGA experts,

Good day!

We were trying to interface our ublox neo M8U gps into the pmod Zedboard using the UART connection. We successfully created the hardware design in vivado by using the axi_uartlite IP in routing the TxD and RxD pins of the gps to the PL  part  of the zedboard (spec. Pmod JB1) and export bitstream in SDk environment. Make some editing of the pre-built code example of axi-uartlite, then finally it runs successfully and we can evaluate the packet that coming out from the gps.

 

Upon checking of the packet results, we noticed that the packet data bytes received each clock time is variable in length and it has a maximum of 16 bytes data only. Our expected total data bytes in each time cycle should be 700 bytes. 

 

Our questions that needs an expert advice:

1. Is this a standard characteristic of axi-uartlite that the received data bytes in each cycle is less than 16 bytes?

2. We need to get our expected total data bytes in every cycle, is this possible? How can we do it in a code?

3. How to make our set-up more efficient in terms of time in parsing the data packets?

 

I will include our code and hardware design below for you to check.

 

Thanks and hoping to hear from the experts.

 

Best regards,

Glenn

 

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/*
* helloworld.c: simple test application
*
* This application configures UART 16550 to baud rate 9600.
* PS7 UART (Zynq) is not initialized by this application, since
* bootrom/bsp configures it to baud rate 115200
*
* ------------------------------------------------
* | UART TYPE BAUD RATE |
* ------------------------------------------------
* uartns550 9600
* uartlite Configurable only in HW design
* ps7_uart 115200 (configured by bootrom/bsp)
*/

#include <stdio.h>
#include "platform.h"
#include "xil_printf.h"
#include "xstatus.h"
#include "ps7_init.h"
#include "xscugic.h"
#include "xparameters.h"
#include "xuartlite.h"
#include "xil_printf.h"

#define TEST_BUFFER_SIZE 700

u8 SendBuffer[TEST_BUFFER_SIZE]; /* Buffer for Transmitting Data */
u8 RecvBuffer[TEST_BUFFER_SIZE]; /* Buffer for Receiving Data */

XUartLite UartLite; /* Instance of the UartLite Device */

int UartLitePolledExample(u32 DeviceId)
{
int Status;

/*
* Initialize the UartLite driver so that it is ready to use.
*/
Status = XUartLite_Initialize(&UartLite, DeviceId);
if (Status != XST_SUCCESS) {
return XST_FAILURE;
}

/*
* Perform a self-test to ensure that the hardware was built correctly.
*/
Status = XUartLite_SelfTest(&UartLite);
if (Status != XST_SUCCESS) {
return XST_FAILURE;
}

 

return XST_SUCCESS;
}

 

int main()
{
int ReceivedCount = 0;
int i;

init_platform();

//enable the pl
ps7_post_config();
// xil_printf("status is %d\n\r",status1);

//enable uartlite
UartLitePolledExample(XPAR_UARTLITE_0_DEVICE_ID);
//xil_printf("status is %d\n\r",Status2);

xil_printf("Hello World, GCP!\n\r");

while(1) {

ReceivedCount = XUartLite_Recv(&UartLite,RecvBuffer,TEST_BUFFER_SIZE);

for(i=0; i<ReceivedCount; i++)
{
xil_printf("ReceivedCount[%d] = %x\n\r" ,i,RecvBuffer);
}
}

cleanup_platform();
return 0;
}

 

[jpeyron]

Hi @gcp,

The buffer size is set at 16 bytes. It sounds like you need to service the buffer more frequently, perhaps this means using interrupts. Another option would be to create a custom uart IP which contains a sizable buffer. Making a custom uart IP is likely more than what you need to do. You might want to look at the 16550 IP core as well.

cheers,

Jon