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- THE Z80 BACK END TABLE
- INTRODUCTION
- This table was written to make it run, not to make it clever!
- The effect is, that the table written for the intel 8080,
- which was made very clever runs faster and requiers less space!!
- So, for anyone to run programs on a z80 machine:
- You could try to make the table as clever as the one for the i80,
- or you could run the i80 table, for that can run on every z80 too.
- IMPLEMENTATION
- It will not be possible to run the entire Amsterdam Compiler Kit on a
- Z80-based computer system.
- One has to write a program on another
- system, a system where the compiler kit runs on.
- This program may be a mixture of high-level languages, such as
- C or Pascal, EM and z80 assembly code.
- The program should be compiled using the compiler kit,
- producing z80 machine code.
- This code should come available to the z80 machine
- for example by downloading or
- by storing it in ROM (Read Only Memory).
- Depending on the characteristics of the particular z80 based system, some
- adaptions have to be made:
- 1) In 'head_em': the base address, which is the address where the first
- z80 instruction will be stored, and the initial value of the
- stackpointer are set to 0x1000 and 0x7ffe respectivally.
- The latter because it could run on a 32K machine as well.
- Other systems require other values.
- 2) In 'head_em': before calling "_m_a_i_n", the environment
- pointer, argument vector and argument count will have to be pushed
- onto the stack.
- Since this back-end is tested on a system without any knowledge
- of these things, dummies are pushed now.
- 3) In 'tail_em': proper routines "putchar" and "getchar" should
- be provided.
- They should write resp. read a character on/from the monitor.
- Maybe some conversions will have to be made.
- The ones for the Nascom and Hermac z80 micro's are to be found
- in the EM-library.
- 4) In 'head_em': an application program returns control to the monitor by
- jumping to address 0x20.
- If this is not the right way on your system, change it.
- For an CPM-machine for example this should be 0x5, to provide a warm boot.
- 5) In 'tail_em': the current version of the z80 back-end has very limited I/O
- capabilities, because it was tested on a system that
- had no knowlegde of files.
- So the implementation of the EM-instruction 'mon' is very simple;
- it can only do the following things:
- Monitor call 1:
- Exit
- Monitor call 3:
- read, always reads from the monitor.
- echos the read character.
- ignores file descriptor.
- Monitor call 4:
- write, always writes on the monitor.
- ignores file descriptor.
- Monitor call 5:
- open file, returns file descriptor -1.
- Monitor call 6:
- close file, returns error code = 0.
- Monitor call 54:
- io-control, returns error code = 0.
- If the system should do file-handling the routine ".mon"
- should be extended thoroughly.
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