Phoebe 2100: I/O, Codec and OS

Wakefield '98

Peripheral I/O

• The Peripheral I/O chip is a similar device to that used in the RiscPC. It is a SMC37665GT, compared to the earlier SMC37665.
• This device handles the standard input/output ports: parallel, serial, serial infra-red (IRDA), PS/2 keyboard & mouse.
• It also acts as an Enhanced IDE (EIDE) controller, allowing up to four devices to be connected to Phoebe.
• The Phoebe interface supports Processor I/O (PIO) Mode 4. It is estimated that this will deliver approximately 16Mbyte/s Peak Data Transfer Rate (DTR), or 10-12Mbyte/s Sustained DTR.
• The RiscPC IDE interface supported PIO Modes 0 and 1, offering 1-2Mbyte/s.
• Phoebe will not support UltraDMA, also known as UDMA.
• Acorn experimented with EIDE DMA Mode 2, upon which UDMA is based, and found that it performed worse that PIO Mode 4. The decision was therefore taken not to implement the DMA system. Acorn's Dave Walker suggested that this result may be due to the way in which Phoebe's DMA system works.

Codec

• Codec stands for Code/Decode.
• The Phoebe Codec IC handles much of the audio processing for the machine.
• It provides "SoundBlaster" support.
• It has a microphone input, and audio mixer, line output and headphone output.
• The Codec also handles the MIDI in/out function (There is no MIDI through).

Operating System

• There are two 40 pin Dual-in-Line sockets provided for the OS ROMs.
• RISC OS 4 is expected to take up 4Mbytes, but the board is capable of supporting 8Mbytes of ROM.
• This extra capacity may be used later to hold, for example, the Java Virtual Machine.

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