Sending ethernet frames using software

[BD00ley]

Hello,

Suppose I already have an ethernet core integrated into my design and wanted to send out a simple ethernet frame using a bare metal program flashed onto it. What might the program look like?
I already tried the following and can see the the preamble and SFD, but the rest of the frame is not I expect and I'm lost on modifying the payload. I appreciate any help that can be offered.

int main(void) {

#ifdef CONFIG_CPU_HAS_INTERRUPT
irq_setmask(0);
irq_setie(1);
#endif

// Random values for parts of the ethernet frame.
const unsigned char macaddr = 0x35;
unsigned int ip = 10;
unsigned short src_port = 0x66;
unsigned short dst_port = 0x77;
unsigned int length = 80;
int status = 0;

uart_init(); 
puts("\nTesting ethernet...\n");
eth_init();
//eth_mode();

// Pointer to payload. Is this correct?
char *payload = (char *)udp_get_tx_buffer;
*payload = 0x00;
printf("Data in payload: %d\n", *payload);
*payload = 0xee;
printf("After writing 0xEE to payload: %x\n", *(char*)udp_get_tx_buffer);

udp_start(&macaddr, ip);
udp_service();
status = udp_send(src_port, dst_port, length);
if(status == 0) 
	printf("Failed to send.\n");
else
	printf("Successfully sent from core.\n");

while(1) {
}

return 0;
}

[enjoy-digital]

Hello @BD00ley,

for bare metal examples, you can have a look at libliteeth from the BIOS:
https://github.com/enjoy-digital/litex/tree/master/litex/soc/software/libliteeth

or uIP drivers:
https://github.com/timvideos/HDMI2USB-litex-firmware/blob/master/firmware/uip/liteethmac-drv.c