Firmware

AN2282

12/19

from the transmit request queue. If there are more transmit requests waiting, then start

the transmission of the next transmit request.

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unsigned short csReadPacketPage( unsigned short Offset );

This reads the PacketPage register at the specified offset.

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void csWritePacketPage( unsigned short Offset, unsigned short

Value );

This writes to the PacketPage register at the specified offset.

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unsigned long csEnqueueTxReq( PIA pDestAddr, mblk_t *pSendParms );

This routine places a transmit request at the end of the Transmit Request queue.

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void csDequeueTxReq(void);

This routine removes a transmit request from the head of the Transmit Request queue.

Summarizing, the lan8900.c module moves the received packet from the Ethernet controller

memory to the reception message and the packet to transmit from the transmission

message to the Ethernet controller memory.

2.2

Device driver

The module ethdev.c is the interface between the CS8900A driver and the TCP/IP stack.

The module also provides the interface to the main routine for Ethernet controller

initialization. The TCP/IP stack is interfaced to the lower layer by a single buffer both for

reception and transmission, so this module has to manage data movement between lower

layer messages and this single buffer. The functions of the module are the following:

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int ethdev_init(void);

The interface for device initialization.

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unsigned int ethdev_read(void);

The interface for processing the events on the Interrupt Status Queue.

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void ethdev_send(void);

The interface to send packets. It copies the TCP/IP stack buffer data into the

transmission message data.

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void ProcessMsg( mblk_t *pMsg );

This routine process the incoming message. It copies the received message data into

TCP/IP stack buffer and returns the length of the received packet avoiding collision

between incoming and outgoing data. Its Entry Point is passed to the lower layer to

indicate which function must process the incoming messages (used to initialize

cs_pAnnounce_Packet variable).

2.3

TCP/IP layers

The TCP/IP stack (uip.c and uip_arp.c modules) used in the solution is the uIP open source

stack from www.sics.se. It provides the necessary protocols for Internet communication,

with a very small code footprint and RAM requirements. The uIP implementation is designed

to have only the absolute minimal set of features needed for a full TCP/IP stack. It can only

handle a single network interface and contains only a rudimentary UDP implementation, but

focuses on the IP, ICMP and TCP protocols. The full TCP/IP suite consists of numerous

protocols, ranging from low level protocol such as ARP which translates IP addresses to

MAC addresses, to application level protocols. The uIP is mostly concerned with the TCP

and IP protocols and upper layer protocols will be referred to as "the application" [6].