A Scheme Interpreter for ARM Microcontrollers: Bugs and "Features" (060)

Known Bugs and "Features"

• STM32 USB:
  Versions: 050 and prior (corrected in 060).
  Pasting code or data into Armpit Scheme on STM32 MCUs connected via USB can result in a jumbled echo of the pasted information. Typing the same code or data manually however produces the correct echo.
• LPC-P1343 USB:
  Versions: 060 (distribution).
  The binary file for the Olimex LPC-P1343 board in the Armpit Scheme 060 distribution does not enumerate properly on the USB interface. It uses USB code from the LPC_1700 mcu_specific directory (file usb.s) but the code is missing a switch to add literals at the end of the file. This is easily fixed by adding the following statements at the end of the mcu_specific/LPC_1700/usb.s file:

  
      .ifdef LPC_13xx
        .ltorg
      .endif
      

  and re-assembling with: ./buildarmpit 060 LPC_1300 LPC_P1343 (see file: buildarmpit). The resulting, updated, binary file is here.
• General:
  Versions: 060.
  When the fast_lambda_lkp performance option is used (default on MCUs with more than 8KB of RAM) built-in functions that are re-defined by the user should be re-defined before other closures using these redefined functions are used. Otherwise, the fast-lookup process will "memoize" the location of the variable binding for the built-in function, rather than its redefinition in the user-environment in which the new closure is itself defined. This interaction is expected to occur only for re-defined built-in functions. A practical impact of this is that the Armpit Scheme prompt cannot be redefined as simply as it could in version 050. In 060, a user-environment binding for the built-in variable prompt does not exist when the rep closure _prg is first executed, and consequently the call to (prompt) in _prg refers to a location in the built-in environment if fast_lambda_lkp is enabled. A way around this is to perform list-surgery on the code of _prg, accessible via: (vector-ref _prg 1), to replace the fast-reference ((# prompt . #)) with '(prompt) or (# . prompt). Redefining the rep also works, but only until the first throw (eg. a ctrl-c) unless the top-level catch is redefined as well: (begin (write (call/cc (lambda (k) (set! _catch k)))) (define (_prg) (write-char #\newline) (prompt) (write (eval (read) (interaction-environment))) (_prg)) (_prg)). This re-definition should be performed after the new, user-space prompt, has been defined. The prompt can then be re-defined at will afterwards (without having to re-re-define the rep). Alternatively, one could re-assemble the source code without fast_lambda_lkp.
• General:
  Versions: 060.
  There are no other known new Bugs and "Features" (or corrected bugs) in this release relative to release 050. Please consult the Change Log to identify other bugs that may have been fixed.

Last updated February 3, 2013