The X-Surf-500 card uses an Asix AX88796B Ethernet chip. It is largely compatible with the classic NE2000 networking chip. Unlike previous networking cards by iComp, the register layout of the chip on the X-Surf-500 is not linear. This is a result of this card being compatible with both the ACA500 and the ACA500plus accelerators, which use a different address line layout on this port. Porting a driver may require a bit more work than just changing a few addresses.
Finding the card
The X-Surf-500 does NOT use Autoconfig. It will just appear at address space $ee.0000 to $ef.ffff once it's installed on the accelerator. Before launching a driver, it may be a good idea to identify the chip first. This may be done by checking the chip version register and reading the first few bytes of the internal memory; you should find the MAC address there, which should start with iComp's address space 28:CD:4C:. If you cannot find this, chances are high that an X-Surf-500 is not connected.
For your convenience, the following table uses similar colours as in the Asix datasheet. Please refer to chapter 5 "Registers operation" of the AX88796B datasheet for a more detailed description of the register bits.
|Chip reg#||Amiga addr||Page 0||Page 1||Page 2||Page 3|
|$00||$ee.0000||CR - command register|
|$04||$ee.2010||TSR(R) / TPSR(W)||PAR3||Reserved||WFBM3|
|$05||$ee.2214||NCR(R) / TBCR0(W)||PAR4||Reserved||WF10CRC|
|$06||$ee.2c10||CPR(R) / TBCR1(W)||PAR5||Reserved||WF32CRC|
|$08||$ee.4080||CRDA0(R) / RSAR0(W)||MAR0||Reserved||WFLB|
|$09||$ee.4284||CRDA1(R) / RSAR1(W)||MAR1||Reserved||WFCMD|
|$0a||$ee.4c80||reserved(R) / RBCR0(W)||MAR2||TFP(R) / Reserved(W)||WUCSR|
|$0b||$ee.4e84||reserved(R) / RBCR1(W)||MAR3||Chip Version(R) / Reserved(W)||PMR|
|$0c||$ee.6090||RSR(R) / RCR(W)||MAR4||RCR(R) / Reserved(W)||Reserved(R) / REER(W)|
|$0d||$ee.6294||CNTR0(R) / TCR(W)||MAR5||TCR(R) / Reserved(W)||MISC|
|$0e||$ee.6c90||CNTR1(R) / DCR(W)||MAR6||DCR(R) / Reserved(W)||GPT0|
|$0f||$ee.6e94||CNTR2(R) / IMR(W)||MAR7||IMR(R) / Reserved(W)||GPT1|
|$10||$ee.0060||16-bit Data port|
|$11||$ee.0264||8-bit Data port|
|(multiple)||$ee.8440||Fifo area: 4 longwords in a row that can be accessed with movem.l|
Use the Fifo area to transfer data using long word accesses. The Fifo area gives you four long words (=16 bytes) in a row that can be accessed using the movem.l command. This will speed up transfers substantially, especially on CPUs without instruction cache. Further, using longword-accesses on the Fifo area (instead of the 16-bit data port) on the ACA500plus with an A1200 accelerator will double the speed of transfers, because two high-speed 16-bit transfers will be combined into a single 32-bit access for the A1200 accelerator. This cuts bus load in half.
The X-Surf-500 uses IRQ level 2 of the Amiga. While the X-Surf-100 has a single IRQ detection bit, the X-Surf-500 only uses the IRQ status register of the Asix chip to identify if an IRQ comes from the Ethernet chip or not. Since the ISR is within paged registers, you will have to carefully check your IRQ service routine for race conditions on the page bits in the command register (CR): Since INT2 is a shared IRQ that is periodically triggered, the IRQ service routine will flip the register page on every INT2. You therefore need to read the page bit status from CR on entry of your service routine, and restore that value before exit.
Data cache considerations
No special care needs to be taken with regard to data caches. As opposed to the X-Surf-100, which may or may not be configured to an address outside the lower 16MB of the system, the X-Surf-500 is always located at $ee.0000. This address space is exempt from data caches on all known accelerators that work with the ACA500 and ACA500plus.