BBCEconet (changes)

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The BBCEconet module provides emulation of certain obsolete OSBYTE and OSWORD calls that were used by the old 6502-based BBC Computers (pre RISC OS), thus making it easier to port code that used these calls.

The purpose of this module is to facilitate the porting of old 6502-based programs. You must not use these calls in any new program or application.

Correspondence between old and new calls

All the calls listed above use exactly the same parameters as their obsolete 6502-based counterparts. The table below details the correspondence between 6502 parameters and ARM RISC OS registers.

Note: Bits 8 – 31 of ARM Registers are ignored.

Implementation Process

• The BBCEconet module claims ByteV and WordV vectors
• If it recognises an OS_Byte or OS_Word call that it supports it checks that the necessary modules are present and active to emulate the call
• Translates the calls to the appropriate SWI call(s) to these modules

Restriction

OS_Byte 50 (poll transmission) and OS_Byte 51 (poll receive block) may enable interrupts and should not be called from within interrupt handlers, service code or event routines. During these calls the processor may be put in USR mode with interrupts enabled; this allows CallBacks to occur.