After completing this lab, you will be able to:
- Utilize the CPU’s private timer in polled mode
- Use SDK Debugger to set break points and view the content of variables and memory
-
If you wish to continue using the design that you created in the previous lab, open the lab4 project from the previous lab, or open the lab4 project in the {labsolutions} directory, and Save it as lab5 to the {labs} directory
Since we will be using the private timer of the CPU, which is always present, we don’t need to modify the hardware design.
-
Open the Block Design. You may notice that the status changes to synthesis and implementation out-of-date as the project was saved as.
Since the bitstream is already generated and will be in the exported directory, we can safely ignore any warning about this. -
In Vivado, select File > Launch SDK
A warning pop-up window indicating that the design is out of date. Since we have not made any changes, we can ignore this.
-
Click Yes.
-
In the Project Explorer in SDK, right click on lab4, lab4_bsp and system_wrapper_hw_platfrom_2 and select Close Project
-
Select File > New > Application Project.
-
Name the project lab5, and for the board Support Package, (Leave Create New for the Board Support Package) and click Next.
-
Select Empty Application and click Finish.
-
Select lab5 > src in the project explorer, right-click, and select Import.
-
Expand General category and double-click on File System.
-
Browse to {sources}\lab5 folder, select lab5.c and click OK, and then click Finish.
You will notice that there are multiple compilation errors. This is expected as the code is incomplete. You will complete the code in this lab.
-
Open the system.mss from lab5_bsp
-
Click on Documentation link corresponding to scutimer (ps7_scutimer) peripheral under the Peripheral Drivers section to open the documentation in a default browser window.
-
Click on the Files link to see available files related to the private timer API.
-
Browse to the source directory, {Xilinx installation}\SDK\2018.1\data\embeddedsw\XilinxProcessorIPLib\drivers\scutimer_v2_0\src and open xscutimer.h link to see various functions available. Look at the XScuTimer_LookupConfig( ) and XScuTimer_CfgInitialize( ) API functions which must be called before the timer functionality can be accessed.
Look at various functions available to interact with the timer hardware, including:
Useful Functions
-
In SDK, in the Problems tab, double-click on the unknown type name x for the parse error. This will open the source file and bring you around to the error place.
First error
-
Add the include statement at the top of the file for the XScuTimer.h. Save the file and the errors should disappear.
#include “xscutimer.h”-
Scroll down the file and notice that there are few lines intentionally left blank with some guiding comments.
Fill in Missing Code
The timer needs to be initialized, the timer needs to be loaded with the value ONE_TENTH*dip_check_prev, AutoLoad needs to be enabled, and the timer needs to be started.
-
Using the API functions list, fill those lines. Save the file and correct errors if any. (Use the completed code further on in this workbook as a guide if necessary.)
Functions needed:
XScuTimer_LookupConfig( ) XScuTimer_CfgInitialize( ) XScuTimer_LoadTimer( ) XScuTimer_EnableAutoReload( ) XScuTimer_Start( )
-
Scroll down the file further and notice that there are few more lines intentionally left blank with some guiding comments.
More Code to be completed
The value of ONE_TENTH*dip_check needs to be written to the timer to update the timer, the InterruptStatus needs to be cleared, and the LED needs to be written to, and the count variable incremented.
Functions needed:
XScuTimer_LoadTimer( ) XScuTimer_ClearInterruptStatus ( ) LED_IP_mWriteReg ( )
6.Using the API functions list, complete those lines. Save the file and correct errors if necessary.
// Include scutimer header file
#include "xscutimer.h"
//====================================================
XScuTimer Timer; /* Cortex A9 SCU Private Timer Instance */
#define ONE_TENTH 32500000 // half of the CPU clock speed/10
int main (void)
{
XGpio dip, push;
int psb_check, dip_check, dip_check_prev, count, Status;
// PS Timer related definitions
XScuTimer_Config *ConfigPtr;
XScuTimer *TimerInstancePtr = &Timer;
xil_printf("-- Start of the Program --\r\n");
XGpio_Initialize(&dip, XPAR_SWITCHES_DEVICE_ID);
XGpio_SetDataDirection(&dip, 1, 0xffffffff);
XGpio_Initialize(&push, XPAR_BUTTONS_DEVICE_ID);
XGpio_SetDataDirection(&push, 1, 0xffffffff);
count = 0;
// Initialize the timer
ConfigPtr = XScuTimer_LookupConfig (XPAR_PS7_SCUTIMER_0_DEVICE_ID);
Status = XScuTimer_CfgInitialize (TimerInstancePtr, ConfigPtr, ConfigPtr->BaseAddr);
if(Status != XST_SUCCESS){
xil_printf("Timer init() failed\r\n");
return XST_FAILURE;
}
// Read dip switch values
dip_check_prev = XGpio_DiscreteRead(&dip, 1);
// Load timer with delay in multiple of ONE_TENTH
XScuTimer_LoadTimer(TimerInstancePtr, ONE_TENTH*dip_check_prev);
// Set AutoLoad mode
XScuTimer_EnableAutoReload(TimerInstancePtr);
// Start the timer
XScuTimer_Start (TimerInstancePtr);
while (1)
{
// Read push buttons and break the loop if Center button pressed
psb_check = XGpio_DiscreteRead(&push, 1);
if(psb_check > 0)
{
xil_printf("Push button pressed: Exiting\r\n");
XScuTimer_Stop(TimerInstancePtr);
break;
}
dip_check = XGpio_DiscreteRead(&dip, 1);
if (dip_check != dip_check_prev) {
xil_printf("DIP Switch Status %x, %x\r\n", dip_check_prev, dip_check);
dip_check_prev = dip_check;
// load timer with the new switch settings
XScuTimer_LoadTimer(TimerInstancePtr, ONE_TENTH*dip_check);
count = 0;
}
if(XScuTimer_IsExpired(TimerInstancePtr)) {
// clear status bit
XScuTimer_ClearInterruptStatus(TimerInstancePtr);
// output the count to LED and increment the count
LED_IP_mWriteReg(XPAR_LED_IP_S_AXI_BASEADDR, 0, count);
count++;
}
}
return 0;
}-
Make sure that micro-USB cable(s) is(are) connected between the board and the PC. Turn ON the power
-
Select Window > Show view > Others.. > Terminal.
-
Click on the connect button and if required, select appropriate COM port (depends on your computer), and configure it with the parameters as shown. (These settings may have been saved from previous lab).
-
Select Xilinx Tools > Program FPGA.
-
Click the Program button to program the FPGA.
-
Select lab5 in Project Explorer, right-click and select Run As > Launch on Hardware (System Debugger) to download the application, execute ps7_init, and execute lab5.elf
Depending on the switch settings you will see LEDs implementing a binary counter with corresponding delay.
Flip the DIP switches and verify that the LEDs light with corresponding delay according to the switch settings. Also notice in the Terminal window, the previous and current switch settings are displayed whenever you flip switches.
Terminal window output
-
Right-click on the Lab5 project in the Project Explorer view and select Debug As > Launch on Hardware (System Debugger).
The lab5.elf file will be downloaded and if prompted, click Yes to stop the current execution of the program.
-
Click Yes if prompted to change to the Debug perspective.
At this point you could have added global variables by right clicking in the Variables tab and selecting Add Global Variables … All global variables would have been displayed and you could have selected desired variables. Since we do not have any global variables, we won’t do it.
-
Double-click in the left margin to set a breakpoint on various lines in lab5.c shown below. A breakpoint has been set when a “tick” and blue circle appear in the left margin beside the line when the breakpoint was set. (The line numbers may be slightly different in your file.)
The first breakpoint is where count is initialized to 0. The second breakpoint is to catch if the timer initialization fails. The third breakpoint is when the program is about to read the dip switch settings. The fourth breakpoint is when the program is about to terminate due to pressing of center push button. The fifth breakpoint is when the timer has expired and about to write to LED.
Setting breakpoints
-
Click on the Resume (
) button to continue executing the program up until the first breakpoint is reached.In the Variables tab you will notice that the count variable may have value other than 0.
-
Click on the Step Over (
) button or press F6 to execute one statement. As you do step over, you will notice that the count variable value changed to 0. -
Click on the Resume button again and you will see that several lines of the code are executed and the execution is suspended at the third breakpoint. The second breakpoint is skipped. This is due to successful timer initialization.
-
Click on the Step Over (F6) button to execute one statement. As you do step over, you will notice that the dip_check_prev variable value changed to a value depending on the switch settings on your board.
-
Click on the memory tab. If you do not see it, go to Window > Show View > Memory.
-
Click the plus sign to add a Memory Monitor
Monitor memory location
-
Enter the address for the private counter load register (0xF8F00600), and click OK.
Monitoring a Memory Address
You can find the address by looking at the xparameters.h file entry to get the base address (
# XPAR_PS7XPAR_PS7_SCUTIMER_0_BASEADDR1), and find the load offset double-clicking on the xscutimer.h in the outline window followed by double-clicking on the xscutimer_hw.h and then selecting XSCUTIMER_LOAD_OFFSET. -
Make sure the DIP Switches are not set to “0000” and click on the Step Over button to execute one statement which will load the timer register.
Notice that the address 0xF8F00604 has become red colored as the content has changed. Verify that the content is same as the value: dip_check_prev*32500000. You will see hexadecimal equivalent (displaying bytes in the order 0 -> 3).
E.g. for dip_check_prev = 1; the value is 0x01EFE920; (reversed: 0x20E9EF01)
-
Click on the Resume button to continue execution of the program. The program will stop at the writing to the LED port (skipping fourth breakpoint as center push button as has not occurred).
Notice that the value of the counter register is changed from the previous one as the timer was started and the countdown had begun.
-
Click on the Step Over button to execute one statement which will write to the LED port and which should turn OFF the LEDs as the count=0.
-
Double-click on the fifth breakpoint, the one that writes to the LED port, so the program can execute freely.
-
Click on the Resume button to continue execution of the program. This time it will continuously run the program changing LED lit pattern at the switch setting rate.
-
Flip the switches to change the delay and observe the effect.
-
Press a push button and observe that the program suspends at the fourth breakpoint. The timer register content as well as the control register (offset 0x08) is red as the counter value had changed and the control register value changed due to timer stop function call. (In the Memory monitor, you may need to right click on the address that is being monitored and click Reset to refresh the memory view.)
-
Terminate the session by clicking on the Terminate button.
-
Exit the SDK and Vivado.
-
Power OFF the board.
This lab led you through developing software that utilized CPU’s private timer. You studied the API documentation, used the appropriate function calls and achieved the desired functionality. You verified the functionality in hardware. Additionally, you used the SDK debugger to view the content of variables and memory, and stepped through various part of the code.