Features

Calculator

Standard Mecrisp-Cube Forth Features

How to Use the Calculator

There are a few differences in operation compared to HP calculators. This applies in particular to entering numbers. Floating-point numbers must have an exponent e.g. 100e, 3.14e, 2.72e0, -10e-12, or end in a metric unit prefix like 10k, 270n, 3.3u.

ENTER reads the number and push it onto the stack. An ENTER without a number do not duplicate the x register (top of stack). If you want to duplicate, you have to use DUP. A stack element is always 32 bit, the content can be float or integer. You have to convert float to integer F→S if you want to use a float number in the integer mode or vice versa S→F.

Warning! If you enter a number with a . but without an exponent e.g. 12.34 Forth interprets this as a double cell integer and put 0 to the x register and 1234 to the y register.

R↓ is actually the Forth word rot, z→y, y→x, x→z.

STO and RCL takes x as register index 0..9.

Caution! If there is an error, the entire stack will be erased. No error message is showed on display, but you can see the error message in the terminal.

RPN crash course.

How it Works

The idea behind this is to use as much of the Forth interpreter as possible. There is already a data stack, but with 64 elements and not only x, y, z, and t registers. The calculator keyboard acts as an ordinary keyboard (terminal), but one key can send several characters (string), e.g. the key COS sends a string " fcos\n". The interpreter executes the float cosinus on the top of the stack. After the successful execution of a line, the stack content is then shown on the display. Digits (0..9, A..F) are forwarded to the display and are interpreted after hitting the ENTER key. If you connect a terminal and hit the TERM key, you can see how the interpreter works.

For implementation details see

About Forth

Forth is an interactive and extensible language, with built-in lexical analysis (tokenizer, parser) and interpreter/compiler, needs less than 20 KiB Flash and 4 KiB RAM, unbelievable for a self-contained (self-hosted) system.

Forth is perfect for embedded systems where some sort of user interactivity like CLI and extensibility (at runtime) are needed.

C & Forth in the 21st Century. C and Forth are both about 50 years old. The combination of the strength of this two worlds results in a powerful system that outperforms other much newer systems like Python. Good design withstands the test of time.

The goal of Mecrisp-Cube is to be a complete Forth programming environment for STM32 MCUs. There are three flavors (branches) available:

May the Forth Be With You!

Use the Terminal (USB CDC)

Connect the WB55 Dongle USB to the PC. Start the terminal emulator application on the PC. Check for the serial communication port (e.g. for Linux /dev/ttyACM0). With tio you can list available devices, look for 4TH devices

$ tio -l
Device            TID     Uptime [s] Driver           Description
----------------- ---- ------------- ---------------- --------------------------
/dev/ttyACM0      38E5      8567.913 cdc_acm          ST-Link VCP Ctrl
/dev/ttyACM1      PESx       873.742 cdc_acm          4TH CDC

By-id
--------------------------------------------------------------------------------
/dev/serial/by-id/usb-spyr.ch_4TH_Calculator_43003F0013504D5943373420-if00
/dev/serial/by-id/usb-STMicroelectronics_STLINK-V3_002700073156501320323443-if02

By-path
--------------------------------------------------------------------------------
/dev/serial/by-path/pci-0000:00:14.0-usb-0:2:1.0
/dev/serial/by-path/pci-0000:00:14.0-usb-0:1:1.2

I set the terminal configuration (e.g. putty) to

With tio

tio --map ICRNL,INLCRNL /dev/serial/by-id/usb-spyr.ch_4TH_Calculator_43003F0013504D5943373420-if00

The greeting screen should apear after pushing the TERM button on the Calculator:

4TH Calculator
--------------
Mecrisp-Cube 1.6.0 deb for STM32WB Nucleo, 63/128 KiB RAM/FLASH dictionary (C) 2024 peter@spyr.ch  * Mecrisp-Stellaris RA 2.5.4 by Matthias Koch.   * Firmware Package STM32Cube FW_WB V1.17.3, BLE Stack 5.3 (C) 2023 STMicroelectronics   * CMSIS-RTOS V2 FreeRTOS wrapper, FreeRTOS Kernel V10.3.1 (C) 2020 Amazon.com  * FatFs for internal flash and microSD - Generic FAT fs module  R0.12c (C) 2017 ChaN  * tiny vi - part of BusyBox (C) 2000, 2001 Sterling Huxley  * TinyUSB CDC, MSC v0.16.0 (C) 2023, hathach (tinyusb.org)

Use the interpreter (reverse polnish notation, like HP calculators):

23 5 / .

This looks like this on your terminal (bold is the Forth answer):

23 5 / .[CR] 4  ok.

The ok. is the Forth prompt and apears at the end of the line (Forth does it differently, like most things ;-). If you don't like it, change it. [CR] is the Enter-key.

The display on the calculator is also updated. The display number mode is probably FLOAT, to see decimal values, hit the DEC button.

Type in your first Forth program (create a word in the RAM dictionray):

: hello ." World" ;

and execute the the program

hello

again the terminal output:

: hello ." World" ;[CR]  ok.
hello[CR] World ok.

The program hello ist not persistent, after power cycle or even reset the RAM dictionray is erased. But it is easy to add a word to the Flash dictionray:

compiletoflash
: hello ." World" ;

The program source is not saved, only the executable machine code is compiled into the flash. You can use the built-in editor vi and save your source to the filesystem either on internal flash drive 0: or on the microSD card drive 1:.

The following part is only for people who are interested how Forth works and have knowledge about the ARM Assembler. There is a built-in disassembler (consider the machine code B500 is 16 bit hex number, but it is stored as 00 B5):

see hello
08043558: B500  push { lr }
0804355A: F7BF  bl  08002BE4  -->  .' World'
0804355C: FB43
0804355E: 5705
08043560: 726F
08043562: 646C
08043564: BD00  pop { pc }

The dictionray entry looks like this (you can see the 'hello' and the string constant 'World'):

$08043558 10 dump
08043550 :  00 00 05 68 65 6C 6C 6F   00 B5 BF F7 43 FB 05 57  | ...hello  ....C..W |
08043560 :  6F 72 6C 64 00 BD 00 00   FF FF FF FF FF FF FF FF  | orld....  ........ |

The compiled word hello needs only 14 bytes in the dictionary.

Buttons, LED

Special Functions on Startup

LEDs as Status Indicator

The LEDs on the dongle displays the status

Acknowledgments


Schematic