This guide is about setting up a debug environment for the Microchip SAME70 Xplained board and compiling Hermes. Other boards might need modification to these proceedures.

OpenOCD is the interface to Atmel's debugger. You need at least version 0.10.0 to get support for the SAME70 board. Note: if you need support for a different debugger interface, you can run ./configure --help to se a list of all supported interfaces. You need to enable your interface at the configuration stage.

# sudo apt install libhidapi-dev libtool autotools-dev pkg-config autoconf automake texinfo libusb-1.0
# git clone https://git.code.sf.net/p/openocd/code openocd-code
# cd openocd-code
# autoreconf -i
# ./bootstrap
# ./configure --enable-cmsis-dap
# make
# sudo make install
                                        

Test the Toolchain

We will now write a simple C program consisting of a stack, a vector table, and a program loop to test gdb and our connection to the board. This has nothing to do with Hermes. We're just checking to see if we can build, load, and run a program with our newly installed tools.

int main(void) ;

unsigned char stack[1024];

void *vectors[]  __attribute__((section(".vectors"))) = {stack+1024, (void*)main};


int main(void) {
    unsigned long long i = 0;
    while(1) {
        i++;
    }
    return 0;
}
                                        

Now compile this with the gcc cross compiler. You will need the right linker script for your device to tell the compiler where code and data should be placed in memory. Hermes comes with linker scripts for the devices it supports, and we'll use the one for the SAME70:

Now start up gdb and load the test.elf binary

# arm-none-eabi-gdb a.out
(gdb) target remote localhost:3333
(gdb) load test.elf

                                        

You should be able to run this simple program now using standard gdb features. You can use layout asm or layout src to view assembly or source for the program as you're stepping through it. You can use layout regs to view the registers.

Download and Build Hermes

# git clone https://bitbucket.org/naklingensmi/hermes.git
# cd hermes
# make
                                        

This will produce an object file called libhermes.a

A simple guest

Below is a simple guest similar to the test program we used above to test gdb. It contains (1) a vector table, (2) startup code, and (3) a main program that runs in an infinite loop.

#include <stdint.h>

void dummyHandler();
void dummyguest();
void __start();

uint8_t dummyStack[1024] __attribute__ ((aligned (32)));

uint32_t *dummyVectorTable[] = {

(void*)dummyStack + sizeof(dummyStack),
(void*)__start,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler,
(void*)dummyHandler };

void __start(){
    asm("ldr r0,=dummyVectorTable\n\
         ldr sp,[r0]"  : : : "r0");
    dummyguest();
}

void dummyHandler() {
    while(1);
}

void dummyguest(){
    uint16_t counter = 0;

    while(1) {
        counter++;
    }
}
                                        

dummyStack is the 1-kB stack for this guest. Each guest must have its own stack, declared as a C-array. dummyVectorTable is the vector table for this guest. We have truncated it to 16 entries, but real apps should have complete vector tables. This should be filled out in exactly the same way as it would be if it were running on the bare metal (not in a hypervisor). __start is the guest's startup code, which initializes the guest's stack pointer and calls the main function.

Now start up gdb and load the test.elf binary

# arm-none-eabi-gdb a.out
(gdb) target remote localhost:3333
(gdb) load test.elf

                                        

You should be able to run this simple program now using standard gdb features. You can use layout asm or layout src to view assembly or source for the program as you're stepping through it. You can use layout regs to view the registers.