Published August 2001

FINE TUNING AN EMBEDDED IDEA

Part 2: Ethernet-Equipped RabbitCore Modules
by Fred Eady

Start • The Networking Core • Code Names and Comedy • Where and Why • Completing Initialization • Down to Business • Now What? • Sources and PDF

THE NETWORKING CORE

It’s pretty obvious that the Rabbit 2000 processor is the computing core of the RCM2100, but the Rabbit 2000 microprocessor by itself cannot implement the lower levels of networking functionality. As far as the RabbitCore RCM2100 is concerned, a UART (on- or off-chip hardware or bit-banged in software) and usually an RS-232 converter IC or similar conversion circuit must be employed to deploy a usable and globally acceptable serial communications interface. The same goes for RS-485. Likewise, the physical and Media Access Control (MAC) of an Ethernet interface are provided by ICs like the Realtek RTL8019AS.

The RTL8019AS is the Ethernet IC of choice for all of the Rabbit Semiconductor core modules and the Z-World BL2000. The hardware implementation of the RTL8019AS is an 8-bit scheme directly connected to the RCM2100 processor. To simplify the RJ-45 end of the interface, an LF1S022 integrated magnetics unit adorns the new models of Ethernet-capable RabbitCore modules. That’s nice, but highly integrated hardware often depends on rock-solid software. Fortunately, Rabbit Semiconductor and Z-World provide full C and assembler source code that describes their Dynamic C Premier library functions. Let’s look at what it takes to bring the RCM2100-mounted RTL8019AS online.

Table 1 is a layout of the RTL8019AS internal registers. The larger and lower portion of Listing 1 is the actual Rabbit code snippet defining the registers laid out in Table 1. The RCM2100 does some ’9346 EEPROM emulation and defines the EEPROM pins (EESK, EEDI, and EEDO) in the code area you see at the beginning of Listing 1. As far as RTL8019AS initialization goes, the idea is to push values into the RTL8019AS internal registers and set up memory areas within the RTL8019AS’s 16 KB of on-chip SRAM for transmit and receive ring buffers.

Some of this register stuffing is normally found in an external serial EEPROM that is specified in the datasheet as a type ‘9346 EEPROM or similar device. One real-life example of this type of serial EEPROM is Atmel’s AT93C46. Tables 2 and 3 show the layout for data contained within the serial EEPROM. The RTL8019AS has to be informed of its base I/O address, interrupt request line, and Ethernet or MAC address, and this data is normally kept within the ’9346.

In the case of the RCM2100, there is no ’9346 physically mounted on the RCM2100 printed circuit board and no provision to add one. The absence of a configuration serial EEPROM is shared by the absence of any configuration jumpers. Bill’s Plug and Play is not a factor here either. So, it’s up to the Dynamic C Premier library routines to trick the RTL8019AS into believing that there is a ’9346 present and programmatically load some useful data into the RTL8019AS’s registers you see in Tables 1, 2, and 3.

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