DHCP Client Functions

7.1DHCP client functions

All DHCP client functions are found in inet\dhcpclnt.c. Many of them also require inet\dhcputil.c to be added to your project. The DHCP client functions are:

•dhc_init()

•dhc_discover() on page 7-3

•dhc_set_callback() on page 7-5

•dhc_halt() on page 7-5

•dhc_second() on page 7-6.

7.1.1dhc_init()

This function initializes the DHCP client. It should be called before attempting to use DHCP to configure any network interfaces. This function attempts to open a UDP connection to listen for incoming replies. After DHCP has been initialized, the application should call dhc_second() one time every second.

Syntax

int dhcinit(void)

Return value

Returns one of the following:

ENP_Code if not successful (see ENP_ error codes on page A-2).

DHCP Client Functions

7.1.2dhc_discover()

This function begins the process of configuring a network interface using DHCP. The process may take several seconds, and the DHCP client will keep retrying if the service does not respond. You should abandon the attempt using dhc_halt() (see dhc_halt() on page 7-5) if the interface is not configured within a reasonable period (such as 30 seconds).

Syntax

int dhc_discover(int net)

where:

Return value

Returns one of the following:

ENP_Code if not successful (see ENP_ error codes on page A-2).

Usage

A simple way to check for completion is to set the IP address for the interface to 0.0.0.0 before starting, and waiting until it becomes nonzero, as illustrated in Example 7-1.

Example 7-1

#ifdef DHCP_CLIENT dhc_init();

for(i = 0; i < MAXNETS; i++)

{

dprintf("Using DHCP to obtain IP address information for interface %d\n", i );

nets[i]->n_ipaddr = 0L; dhc_discover(i);

}

do {

tk_yield(); e = 0;

for(i = 0; i < MAXNETS; i++)

{

DHCP Client Functions

if ( nets[i]->n_ipaddr ) e++;

}

} while ( e != MAXNETS );

dprintf("All interfaces are now configured.\n" ); #endif

As an alternative to polling the IP address, you can install a callback to signal completion. See dhc_set_callback() on page 7-5 for details.

DHCP Client Functions

7.1.3dhc_set_callback()

This function installs a callback to be used to signal that the configuration of an interface is complete. This allows a multi-threaded RTOS to use DHCP without the overhead of polling loops.

Syntax

void dhc_set_callback(int net, int(*routine)(int net))

where:

routine is the function to call when configuration is complete. This will receive the index of the interface as its argument.

Return value

None.

Usage

This function would be used to inform the application that the network interface is now available for use. It will typically do this by setting a volatile flag, or by signalling the RTOS thread(s) which were waiting for the interface.

7.1.4dhc_halt()

This function stops all DHCP activity on a network interface.

Syntax

void dhc_halt(int net)

where:

Return value

None.