How to pass a 48-bit MAC address as a arguement in a function through a uint_8-bit variable? - c++

Question

Recently, I started working on a project relevant to emac and came across few doubts and blockages with respect to implementation, and decided to post my Q here to get some advise and suggestions from experienced people.
At present, I am working on interfacing the EMAC-DM9161A module with my SAM3x - Taiji Uino board for high speed ethernet communication.I am using the library developed by Palliser which is uploaded on Github as elechouse/EMAC-Demo. In the source code - ethernet_phy.c, I came across this function to initialize the DM9161A PHY component as follows:
unit8_t ethernet_phy_init(Emac*p_emac, uint8_t uc_phy_addr, uint32_t mck);
Problem: The argument uint8_t uc_phy_addr is an 8 bit register through which I want to pass a 48 bit MAC address such as - 70-62-D8-28-C2-8E. I understand that, I can use two 32 bit registers to store the first 32 bit of the MAC address i.e. 70-62-D8-28 in one 32 bit register and the rest 16 bit MAC address i.e. C2-8E in another 32 bit register. However, I cannot do this, since I need to use the above ethernet_phy_init function in which a unit8_t is used to pass the 48 bit MAC address. So, I'd like to know, how to make this happen?
Another Question: I executed some code to understand by some trial methods and came across some doubts,here is the code:
int main()
{
unit8_t phy_addr =49; //Assign a value 49 to 8 bit Reg
int8_t phy_addr1 = 49;
int phy_addr2 = 49;
cout<<phy_addr;
cout<<phy_addr1
cout<<phy_addr2;
getchar();
return 0;
}
Output Results:
1
1
49
So my doubt is, why is the output being displayed in ASCII character wherever I use a 8 bit variable to store the value 49, but when I use a normal 32 bit int variable to store 49, it displays a decimal value of 49. Why does this happen?. And lastly how to store MAC address in an 8 bit register?

Answer 1

About second question:
uint8_t/int8_t is same as unsigned/signed char and cout will handli it as char. Use static_cast<int> to print as number.
About first quiestion:
I never worked with emac, but judging by this example mac should be set this way:
#define ETHERNET_CONF_ETHADDR0 0x00
#define ETHERNET_CONF_ETHADDR0 0x00
#define ETHERNET_CONF_ETHADDR1 0x04
#define ETHERNET_CONF_ETHADDR2 0x25
#define ETHERNET_CONF_ETHADDR3 0x1C
#define ETHERNET_CONF_ETHADDR4 0xA0
#define ETHERNET_CONF_ETHADDR5 0x02
static uint8_t gs_uc_mac_address[] =
{ ETHERNET_CONF_ETHADDR0, ETHERNET_CONF_ETHADDR1, ETHERNET_CONF_ETHADDR2,
ETHERNET_CONF_ETHADDR3, ETHERNET_CONF_ETHADDR4, ETHERNET_CONF_ETHADDR5
};
emac_options_t emac_option;
memcpy(emac_option.uc_mac_addr, gs_uc_mac_address, sizeof(gs_uc_mac_address));
emac_dev_init(EMAC, &gs_emac_dev, &emac_option);

Answer 2

Regarding your second question: the first 2 variables are 8bit (one signed and one unsigned), so the ostream assumes they are chars (also 8bit wide) and displays the char representation for them ("1" = ASCII 49).
As for original question, i browsed a little bit the Atmel sources and the MAC address has nothing to do in ethernet_phy_init (all is at a much lower level):
uc_phy_addr - seems to be interface index
mck - seems to be a timer related value.

Answer 3

I figured it out, so I am going to answer my own question for those beginners like me who may encounter this same doubt.
Answer: As suggested by the members in the comments, yes they were right and thanks to them. The function parameter uint8_t uc_phy_addr represents the 5 bit port address in the PHY chip - Register and not the MAC Address, hence the address is set as 0x01 to enable only the receive pin and keeping the other 4 bits 0. The 4th bit is the CSR which is also set 0 in this case (for more details, Please refer data sheet of DM9161A).