A500-sd plus controller

a500-sd-plus-controller

This is a dual micro-SD card plus Ethernet controller for the Amiga 500. The controller piggybacks on the odd CIA (CIA A) chip on the Amiga 500 motherboard.

Table of Contents

• Micro-SD
• Ethernet
• Drivers
• Performance
• Pictures
• Building

Micro-SD

The two Micro-SD cards are operated in SPI mode. Using the 68000 movep (move to/from peripheral) instruction and optimized code the driver reaches a raw throughput of up to 450kB/s on a standard 7MHz 68000 CPU. Due to device driver and filesystem overhead the overall speed is lower though.

The primary channel is intended for internal use. The micro-SD card in this slot functions as a fixed harddisk. The secondary channel is intended to be used with an extension cable to hold an external (hot-swappable if the driver supports it) micro-SD card. For this purpose, proper measures are taken to control signal integrity over the extension cable. The controller can also handle any current surges that can occur during hot swapping without overloading the Amiga power rail.

Ethernet

The Ethernet controller is a Microchip ENC28J60 device. It is also connected over SPI and uses the INT2 interrupt. The ENC28J60 supports a 10Mbit network connection. The interface is built in a slightly non-standard way to maximum immunity for external interference.

Drivers

The Micro-SD cards are supported by sd-lide.device.

The Ethernet controller is supported by enc28j60.device.

Performance

On a standard Amiga 500 with a 7MHz 68000 CPU running OS3.1 and AmiTCP 3.0b2 the following performance is reached:

• 250kB/s read speed for the Micro-SD cards as reported by SysInfo.
• Up to 22kB/s network download speed which is mostly limited by CPU speed.

Much better performance which is only limited by the speed of the E-clk (~600..700kB/s) can be expected when a faster CPU is installed.

Pictures

Proof that this was actually built:

And the obligatory SysInfo screenshot:

Building

Under releases you will find the latest gerbers, bill of materials, bitstream, etc. The files are in a format that is suitable for most well-known PCBA manufacturers. I would recommend having the boards soldered professionally. This project uses small compononents and especially the CPLD is not solderable by hand. I had the boards made with all the SMD parts and the ethernet connector mounted. I only soldered the pinheaders and the CIA socket myself. For the pinheaders that plug into the CIA socket on the A500 motherboard, be sure to use the THIN and ROUND (aka "turned") pinheaders. Otherwise the motherboard socket WILL be damaged.