SMSC LAN91C111 6.5Software Considerations for Big Endian

SMSC LAN91C111 32/16/8-Bit Three-In-One Fast Ethernet Controller

Figure 6.2 16-bit Byte Lane Configuration

As you can see the lower byte lane (Byte Lane 0) on the LAN91C111 becomes the upper byte lane on the processor. The second byte lane (Byte Lane 1) becomes the lower byte of the upper word on a 32bit interface. The third byte lane (Byte Lane 2) becomes the upper byte of the lower word on a 32bit interface and the upper byte on a 16bit interface. The third byte lane (Byte Lane 3) becomes the lower byte of low word on a 32bit interface and the low byte of the low word on a 16bit interface.

6.5Software Considerations for Big Endian

Converting data between the two systems is sometimes referred to as the NUXI problem. Imagine the word UNIX stored in two 2-byte words. In Big Endian systems, it would be stored as UNIX. In a Little- Endian system, it would be stored as NUXI. As previously described, this is only an issue on 16/32bit architectures and is not a problem if using an 8bit endian style microcontroller.

The way data is read and written to the Ethernet port does not require software to do byte swapping BUT for configuration of the internal data registers the software will be required to byte swap information to accommodate the physical connection. When you initialize the LAN91C111 from a endian architecture machine you will need to take into consideration the differences in endianness when writing your initialization routines and the way that the host processor is connected to the LAN91C111 device. This is where the software comes into play. Through software you can accommodate the differences in endianness.

SMSC AN 9.6

39

Revision 1.0 (08-14-08)

APPLICATION NOTE

Contents

1 Overview 1.1Audience 2 Introduction Page 3 Description Of Bus Interface Unit (BIU) 3.2ISA Bus 3.38-BitBus 3.3.1Address Decoding Example 3.3.2I/O Base Address 300h Decoding 3.4Asynchronous Interface 3.4.1Typical Signal Connection with Asynchronous Buses 3.4.2Signal Connection with Asynchronous Interfacing 3.5Synchronous Interface (VL-Bus) 3.5.1Typical Connection with Synchronous Interface (VL-Bus) 3.5.2Signal Connection with Synchronous Interfacing LAN91C111 3.5.3Address Bus 3.5.4AEN 3.5.5W/NR 3.5.6NRDYRTN 3.5.7NSRDY 3.5.8LCLK – Clock Input 3.5.9Reset 3.5.10 NBE0-NBE3 3.6Timing Analysis 3.6.1Write Cycle Address Phase - Cycle Start 3.6.2Write Cycle Data Phase - Cycle End 3.6.3Read Cycle 3.6.4Read Cycle Address Phase – Cycle Start 3.6.5Read Cycle Delay Phase 3.6.6Read Cycle Data Phase – Cycle End 3.7Direct Data Register Access interface (nDATACS) 3.7.1The Use of NDATACS 3.7.2Pointer Register 3.7.3Data Register 3.7.4Timing Analysis Of Direct Access 3.8Asynchronous Read or Write Operation – Non Burst 3.9Burst Mode Operation Timing – Synchronous Operation 3.10 Burst Mode Write Operation 3.11 Burst Mode Read Operation 3.12 LAN91C111 Bus Interface 3.13 Sample Routine of Performance Measurement and Tuning Flow Chart 4 System Hardware Design 4.1Quartz Crystal 4.2Clock Oscillator 4.3X25OUT 4.4Serial EEPROM Operation 4.4.1INDIVIDUAL ADDRESS 20-22hex 4.4.2Use the Serial EEPROM as an Option 4.4.3How to Change the IOBASE Address 4.5Power Supply Decoupling 4.6System Power Consumption 4.7Auto Negotiation 4.7.1Initialization Sequence Steps Page 4.9Loopback 4.9.1EPH Internal Loopback (MAC) 4.9.2Diagnostic Loopback 4.9.3External Loopback Page 4.10 LED Operation 4.10.1LED Description 4.11 Thermal Information 5 Memory Management Unit - Features and Benefits 5.1Memory Partitioning 6 Big and Little Endian Issues on the LAN91C111 6.1Introduction 6.2Definition 6.2.1Big Endian 6.2.2Little Endian 6.3Implications for the LAN91C111 6.4Physical connections for Big Endian Page 6.5Software Considerations for Big Endian 6.6Source Code Example Page 6.6.1Conclusion 7 Physical Layer and Magnetics 7.1Transmit / Receive Interface 7.1.1Transmit Interface 7.1.2Receive Interface 7.1.3Magnetics 7.2RBIAS 7.2.1RBIAS pin 7.2.2TP Transmit Output Current Set 7.2.3Cable Selection 7.2.4Transmitter Droop 7.3MII Management Functions 7.3.1Example Routines To Read and Write the PHY Registers Page Page Page 7.4Multiple Register Access 8 Reset Operation 9 Functional Test and Diagnostic 9.1MAC Register Test 9.2RAM Buffer Test 9.3Transmitting A Packet 9.4Releasing The Transmitted Packet 9.5Receiving A Packet 9.6Releasing A Received Packet 9.7EPH Loopback Test 9.8PHY Loopback Test 9.9External Loopback Test 9.10 MMU Test Page 10 Migrating From LAN91C100FD and LAN83C183 to LAN91C111 10.1 91C111 Overview 10.2 New Features and Modification 10.2.1 Receive/PHY Control Register 10.2.2Memory Information Register 10.2.3 RX_OVRN bit 10.2.4 MDINT Interrupt bit 10.2.5Internal PHY Registers 10.2.6Media Independent Interface (MII) 10.2.7 Power Management 10.2.8Internal PHY and External PHY Selection 10.2.9 General Purpose Output 10.2.10 Reset 10.2.11 Interrupt Pin (INTR0) 10.2.12 SRAM Interface 10.2.13X25OUT Clock Output Pin 11 Design and Layout Check Guidelines