Framework content

C start up code

(c_programs/c_support/crt)

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Coded in as-z80 assembler.

• save FLOS stack ptr
• save ptr to command line args
• set own stack
• call gsinit (init global C vars)
• call main()
• restore original FLOS stack ptr
• exit to FLOS, with exit code returned by main()

OS interface - asm proxy

(c_programs/c_support/os_proxy)

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Coded in pasmo assembler.
Have a “data exchange” area (between C and asm code) at offset 0. (area len is $20 bytes)
Actual code start at offset $20.
For each FLOS procedure:

• push all regs
• get args from “data exchange” area to z80 regs
• call FLOS
• store returned values from z80 regs to “data exchange” area
• pop all regs

Compilation process:

• proxy source code flos.asm compiled to flos.asm.bin
• flos.asm.bin (binary) converted to flos_proxy_code.c (C source code)
• flos_proxy_code.c compiled and linked to user program, at address $5080.

(For conversion from binary to C source file, xd.exe utility used.)

OS interface for C

(c_programs/c_support/os_interface_for_c)

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This is a C file, which contain FLOS C functions.
Each function do the following:

• copy function arguments to “data exchange” area
• call “asm proxy”
• copy returned results from “data exchange” area to C vars

The call chain is:

• user program call C function in “OS interface for C”
• “OS interface for C” call “asm proxy”
• “asm proxy” call FLOS code

Current status

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• number of C FLOS function implemented: about 30 (see inc\os_interface_for_c\i_flos.h for complete list)
• asm proxy compiled size: about 1,8 KB

The content of “obj” folders is auto generated by SDCC compiler and linker.

Executable file map

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Start address 5000.

Offsets in file	Description
0000	C start up code
0080	asm proxy
0080	asm proxy - “data exchange” area
00a0	asm proxy - actual code
CODE	start of code
DATA	start of data

(you set CODE and DATA values and also STACK value, in your project Makefile)