Sinclair Scientific Calculator Emulator alternative software written in Rust

Alternative implementation for Sinclair Scientific calculator board.

Build Instructions

1. Install prerequisites as described in the avr-hal README (avr-gcc, avr-libc, avrdude, ravedude).
2. Use nightly-2024-03-22 toolchain.
3. Run cargo build --release to build the firmware (debug builds won't work for now).
4. Run RAVEDUDE_PORT=/dev/ttyUSB0 cargo run --release to flash the firmware to a connected board. If ravedude fails to detect your board, check its documentation at https://crates.io/crates/ravedude.
5. ravedude will open a console session after flashing where you can interact with the UART console of your board.

License

• LICENSE-APACHE

Floating point support

Error linking when using f64, undefined reference to:

__divdf3
__gedf2
__gtdf2
__ltdf2
__muldf3
__nedf2
__subdf3

Use f32 as f64 are not supported by avr-libc.

Error linking src/float/add.rs:161: more undefined references to 'core::panicking::panic' follow

• Goes away when using --release builds
• https://github.com/rust-lang/compiler-builtins/issues/245

Error multiple definition of '__addsf3'

          (.text.avr-libc.fplib+0x2): multiple definition of `__addsf3';
          avr-calc/target/avr-atmega328p/release/deps/libcompiler_builtins-ff74a4526ccb7313.rlib(compiler_builtins-ff74a4526ccb7313.compiler_builtins.63915e056af5b1f3-cgu.0.rcgu.o):
          .cargo/registry/src/index.crates.io-6f17d22bba15001f/compiler_builtins-0.1.108/src/macros.rs:500: first defined here

objdump -t target/avr-atmega328p/release/deps/libcompiler_builtins-ff74a4526ccb7313.rlib | grep __addsf3
00000000 l    d  .text._ZN17compiler_builtins5float3add8__addsf317h33c25ff7dd1591e8E	00000000 .text._ZN17compiler_builtins5float3add8__addsf317h33c25ff7dd1591e8E
00000000 l    d  .text.__addsf3	00000000 .text.__addsf3
00000000 g     F .text._ZN17compiler_builtins5float3add8__addsf317h33c25ff7dd1591e8E	0000085c .hidden _ZN17compiler_builtins5float3add8__addsf317h33c25ff7dd1591e8E
00000000 g     F .text.__addsf3	00000006 .hidden __addsf3

• https://github.com/rust-lang/compiler-builtins/tree/master/compiler-builtins
• compiler-builtins also implements software floats and this collides with libm from avr-lib.
  • It provides __adddf3 and __addsf3 but not __divdf3 and others listed above?
  • The __addsf3 is provided by both libs, avr-lib does not provide f64 variants and builtins some operations are missing?
• Compiling with no default libraries and just libc (for mem* functions) still does not work as it imports __addsff3:

  = note: /usr/bin/avr-ld:
    /usr/lib/gcc/avr/9.3.0/../../../../avr/lib/avr5/libc.a(addsf3.o): in function `__addsf3':
        (.text.avr-libc.fplib+0x2): multiple definition of `__addsf3';
    target/avr-atmega328p/release/deps/libcompiler_builtins-0dbc77ea0d873946.rlib(compiler_builtins-0dbc77ea0d873946.compiler_builtins.88514279ac67cc58-cgu.0.rcgu.o):index.crates.io-6f17d22bba15001f/compiler_builtins-0.1.108/src/macros.rs:500: first defined here

avr-libc

• https://github.com/avrdudes/avr-libc
• Only f32 are implemented: https://github.com/avrdudes/avr-libc/tree/main/libm/fplib

The atmega328p uses libraries from /usr/avr/lib/avr5/ and it contains libm.

libm.a contains all the missing symbols but with sf instead of df.

• objdump -t /usr/avr/lib/avr5/libm.a | grep fp
• sf3 single (f32) float
• df3 double (f64) float
• https://gcc.gnu.org/onlinedocs/gcc-3.4.0/gccint/Soft-float-library-routines.html

float __divsf3 (float a, float b)
double __divdf3 (double a, double b)

Setting "no-default-libraries": true, in avr-specs/avr-atmega328p.json excludes libm, adding -lm and -lc works.