uBasicPlus is an extension of the uBasic by Adam Dunkels (2006), https://github.com/adamdunkels/ubasic, which includes the strings and their functions from 'uBasic with strings' by David Mitchell (2008), http://www.zenoshrdlu.com/kapstuff/zsubasic.html, and some constructs and interpreter logic from 'CHDK', http://chdk.wikia.com/wiki/CHDK_Scripting_Cross_Reference_Page.

• UBASIC, which can be a small non-interactive interpreter of the programming language BASIC which offers a subset of the commands that are part of the language, 26 integer variables, named 'a' through 'z', if/then/else with support for single symbol logical operators (>,<,=), for/next, let, goto, gosub, print and '\n' (new line) as end-of-line character.

• uBasic with strings, which adds support for strings: 26 string variables, named a$-z$, string literals, variables and expressions can be used in assignments and print statements string expressions can be compared for equality in if statements string expressions can be concatenated using '+', and a number of string functions: left$, mid$, right, str$, chr$, val, len$, instr$, asc.

  What is new in UBASIC-PLUS is that string scratch space (SSS) is introduced in which all string variables and intermediate results are stored using a structure header (1byte) + data (strlen+1 bytes). At the end of each statement the SSS is cleared of all non-assigned strings. This means that rather than pointers (size 4 bytes) the addresses in the space are used (2 bytes). This caused all string functions to be rewritten. Most importantly, the garbage collection is done in place rather then by temporarily doubling the storage space. The garbage collection now used is similar to the garbage collection done for managing arrays.

• Elements of CHDK

  The line numbering is removed and replaced by the labels CHDK-style

  :label1
  ....
  goto label1;
  

  What is new in UBASIC-PLUS is that when these labels are refered to in goto/gosub this is done without quotation marks (unlike CHDK). Furthermore, in labels '_' can be used. Not even internally the lines are numbered (like it was the case with CHDK). Rather, pointers are used to script string, meaning that the returns - from gosub, for/next, if/then/else, while/endwhile - are faster as they do not require searches (over line numbers).

• Strings can be encompassed by single or double quotations. Tokenizer can identify labels.

• End of line characters '\n' and ';'

• config.h

  Allows user to select which of the features below (if any) they want in their uBasic build.

• Fixep point floats are implemented through Fixed Point Math Library for C by Ivan Voras and Tim Hartnick, https://sourceforge.net/projects/fixedptc. The libary is enhanced with str_fixedpt function, which converts a string to fixed point float.

• flow control

  • more logical operators supported (<>,<=,>=,==,&&,||,!)
  • complex logical expressions supported with use of brackets
  • multi-line If/then/else/endif-command (CHDK-style)
  • while/endwhile

• input {a,a$,a@(i)}, timeout_ms

  Wait at most until timeout_ms for input from the serial port. Wait is not executed inside the interpreter. Relies on external functions for serial-available and serial-read to be supplied as documented in config.h .

• 26 fixed point arrays, a@ to z@, dynamically allocated using DIM command,

  dim a@(5);
  for i = 1 to 5;
    input a@(i),10000;
  next i;
  

  In this example code expects 5 array entries to be entered through serial port, and waits at most 10sec for each input to complete. In the scripts or from the input line the numbers can be entered either directly as hex values,

  ... x = 0xaabbccdd
  

  or as binary values,

  ... x = 0b1101001
  

  or as decimal values,

  ... x = 123456[d,D,L,l]
  

  if the default fixed point float is not desired.

• println

  Same as print but adds an empty line at the end. Additional identifiers hex or dec can be used to print the number as (hex)adecimal if fixed point floats are not desired, as in this example:

  ... println [hex,dec] x 
  

• sleep(f)

  Wait f seconds, which can be fixed point float. This is not executed inside the BASIC interpreter.

• ran, uniform

  System random number generators based on the external function as documented in config.h . On STM32 boards listed below, ran and uniform use two lowest bits after the analog read from the internal temperature sensor. From multiple calls required number of random bits is collected.

  • ran - generates random positive integer in fixed point float representation.

  • uniform - generates random fixed point float in the range 0 to 0.999.

• tic(n), a=toc(n)

  rlabplus-type six timers for measuring the passed time from different breakpoints in the script

• sqrt, sin, cos, tan, exp, ln, pow

  fixed point arithmetic single argument functions from the fixed point math library.

• floor, ceil, round, abs

  fixed point float to fixed point integer arithmetic functions.

• clear

  Clears all variables, arrays and strings. It is good practice to put it as the first line of the script.

• pinmode(pin,mode,speed), a=dread(pin), dwrite(pin,state)

  Allows direct control over digital pins.

  • pin:

    The pin designation follows their hardware names, 0xa0:0xaf for pins 0 through 15 on port A, and so forth. It is up to user to verify that particular pins are available for digital read/write operations. Tied to hardware specific functions as described in config.h .

  • mode: STM32 specific

    Output: -2 for open drain, -1 for push-pull

    Input: 0 for no pull, 1 for push-up, 2 for push-down.

  • speed: STM specific

    0 for low, 1 for medium and 2 for high frequency.

• awrite_conf(prescaler,period), awrite(channel,value), awrite(channel)

  direct control over output pins that support PWM on the micro-controller. The value has to be in the range 0 to period-1. Tied to hardware functions described in config.h

• i = flag(channel)

  Allow flags that can be set outside BASIC interpreter, e.g., using interrupts, to be used in flow control.

  :waithere
      if (flag(1)==0) then goto waithere;
  

  In this example the script sits in this loop until the hardware event flag no. 1 gets set by external process. Importantly, after the interpreter recognizes that the flag has been set, it immediately resets it so the subsequent calls will return 0 until the flag is set again externally.

  Importantly, while waiting for the flag, the microcontrolled does not sit inside the interpreter.

• aread_conf(duration,nreads), i = aread(channel)

  Read input from analog channels 0:18 from the microcontroller. The pin assignments of the analog inputs for some microcontrollers is given in hardware examples below. Some channels may not be available.

  • duration: STM specific

    0 through 7 for varius preprogrammend duration of analog sampling and conversion, higher the value longer the duration.

  • nreads: value reported to the user will be an average of so many readings.

• store(x[x$,x@]), i=recall(x[x$,x@])

  Store and recall variable, string or array in FLASH. In that way variable can survive reboot of the device. The single page from FLASH is used as a scratch space, so when there is no more space left on the page, the entire page is erased.

The Command Line Interface (CLI) supports the following commands:

• prog

  The CLI enters the line input mode. Everything entered on the serial port is considered as a sequential line in the script. Repeated execution of prog erases the previous script.

• run

  The CLI executes what ever has been assembled from multiple inputs as a BASIC script.

• cat

  Print the script that has been assembed so far.

• save

  exit the prog mode.

• edit

  enter the prog mode. Subsequent lines of input will be attached to already existing script.

• demo N

  execute demo script number N.

• kill

  Stops the script if it is being executed, and returns control to command prompt.

• If in prog mode, every typed line is added to the script until save or run is executed.

• If not in prog mode, every typed line is executed as its own script, but the uBasic-Plus internal storage is not erased in between the executions.

The uBasic-Plus comprise of six files config.h, fixedptc.h, tokenizer.c, tokenizer.h, ubasic.c and ubasic.h. As an example implementation of the hardware related functions (random number generation, gpio, hardware events, sleep and tic/toc) the development boards STM32F030-Nucleo64 and STM32F051-Discovery are used in combination with CubeMX created system libraries.

println 'Demo 1 - Warm-up'
gosub l1
for i = 1 to 2
  for j = 1 to 2
    println 'i,j=',i,j
  next j
next i
println 'Demo 1 Completed'
end
  :l1
println 'subroutine'
return

println 'Demo 2'
a$= 'abcdefghi'
b$='123456789'
println 'Length of a$=', len(a$)
println 'Length of b$=', len(b$)
if len(a$) = len(b$) then println 'same length'
if a$ = b$ then println 'same string'
c$=left$(a$+ b$,12)
println c$
c$=right$(a$+b$, 12)
println c$
c$=mid$(a$+b$, 8,8)
println c$
c$=str$(13+42)
println c$
println len(c$)
println len('this' + 'that')
c$ = chr$(34)
println 'c$=' c$
j = asc(c$)
println 'j=' j
println val('12345')
i=instr(3, '123456789', '67')
println 'position of 67 in 123456789 is', i
println mid$(a$,2,2)+'xyx'
println 'Demo 2 Completed'
end

println 'Demo 3 - Plus'
tic(1)
for i = 1 to 2
  j = i + 0.25 + 1/2
  println 'j=' j
  k = sqrt(2*j) + ln(4*i) + cos(i+j) + sin(j)
  println 'k=' k
next i
:repeat
  if toc(1)<=300 then goto repeat
for i = 1 to 2
println 'ran(' i ')=' ran
next i
for i = 1 to 2
println 'uniform(' i ')=' uniform
next i
for i = 1 to 2
x = 10 * uniform
println 'x=' x
println 'floor(x)=' floor(x)
println 'ceil(x)=' ceil(x)
println 'round(x)=' round(x)
println 'x^3=' pow(x,3)
next i
println 'Digital Write Test'
pinmode(0xc0,-1,0)
pinmode(0xc1,-1,0)
pinmode(0xc2,-1,0)
pinmode(0xc3,-1,0)
for j = 0 to 2
  dwrite(0xc0,(j % 2))
  dwrite(0xc1,(j % 2))
  dwrite(0xc2,(j % 2))
  dwrite(0xc3,(j % 2))
  sleep(0.5)
next j
println 'Press the Blue Button or type kill!'
:presswait
  if flag(1)=0 then goto presswait
tic(1)
println 'Blue Button pressed!'
:deprwait
  if flag(2)=0 then goto deprwait
println 'duration =' toc(1)
println 'Blue Button de-pressed!'
println 'Demo 3 Completed'
end

println 'Demo 4 - Input with timeouts'
dim a@(5)
for i = 1 to 5
  print '?'
  input a@(i),10000
next i
println 'end of input'
for i = 1 to 5
  println 'a(' i ') = ' a@(i)
next i
println 'Demo 4 Completed'
end

println 'Demo 5 - analog inputs and arrays';
for i = 1 to 100;
  x = aread(16);
  y = aread(17);
  println 'VREF,TEMP=', x, y;
next i;
for i = 1 to 1;
  n = floor(10 * uniform) + 2 ;
  dim b@(n);
  for j = 1 to n;
    b@(j) = ran;
    println 'b@(' j ')=' b@(j);
  next j;
next i;
println 'Demo 5 Completed';
end;

println 'Demo 6: Multiline if, while'
println 'Test If: 1'
for i=1 to 10 step 0.125
  x = uniform
  if (x>=0.5) then
    println x, 'is greater then 0.5'
  else
    println x, 'is smaller then 0.5'
  endif
  println 'i=' i
next i
println 'End of If-test 1'
println 'Test While: 1'
i=10
while ((i>=0)&&(uniform<=0.9))
  i = i - 0.125
  println 'i =', i
endwhile
println 'End of While-test 1'
println 'Demo 6 Completed'
end

println 'Demo 7: Analog Read or Kill'
y=0
:startover
  x = aread(10)
  if (abs(x-y)>20) then
    y = x
    println 'x=',x
  endif
  sleep (0.2)
  goto startover
end

println 'Demo 8: analog write (PWM) 4-Channel Test'
p = 65536
for k = 1 to 10
  p = p/2
  awrite_conf(p,4096)
  println 'prescaler = ' p
  for i = 1 to 10
    for j = 1 to 4
      awrite(j,4095*uniform)
    next j
    println '    analog write = ' awrite(1),awrite(2),awrite(3),awrite(4)
    sleep(5)
  next i
next k
awrite(1,0)
awrite(2,0)
awrite(3,0)
awrite(4,0)
end

clear
println 'Demo 9: store/recall with FLASH'
if (recall(x)==0) then
  println 'generating x'
  x = uniform
  store(x)
endif
println 'stored: x=' x
if (recall(y@)==0) then
  println 'generating y'
  dim y@(10)
  for i=1 to 10
    y@(i) = uniform
  next i
  store(y@)
endif
println 'stored: y@'
for i=1 to 10
  println '  y@('i')=' y@(i)
next i
if (recall(s$)==0) then
  println 'generating s'
  s$='what is going on?'
  store(s$)
endif
println 'stored: s$',s$
println 'Demo 9 Completed'
println 'Please run it once more'
end

• STM32F0

  For both boards a HAL UART library with RX using circular buffer was implemented and tested. The library provides Arduino-type serial-available and serial-read functions. The library is the same for both STM32F0 boards. The library is located in Drivers folder and should replace the same by STM.

About the board:

• Arm Cortex M0 64kb flash, 8kb ram, 48MHz frequency

• GPIO: PC0, PC1, PC2, PC3

• PWM: Timer 3 Channels 1 (PA6), 2 (PA7), 3 (PB0) and 4 (PB1)

• Analog Input: On STM32F0 these Channels are mapped to pins as follows 0:7 as A0:A7, 8:9 as B0:B1, and 10:15 as C0:C5. Channel 16 is the temperature, and 17 the VREF.

• Hardware Events:

  • Blue Push Button 1 (PC13) with two events:
    • button pressed - flag(1), and
    • button depressed - flag(2)

• sleep, tic/toc:

  through SysTick_Handler() which counts in 1ms increments through interrupts

• Serial Port

  through USB connector used for debugging (UART2 on PA2/PA3)

About the board:

• Arm Cortex M0 64kb flash, 8kb ram, 48MHz frequency

• GPIO: PC0, PC1, PC2, PC3

• PWM: Timer 3 Channels 1 (PC6), 2 (PC7), 3 (PC8/LED4-blue) and 4 (PC9/LED3-green)

• Analog Input: On STM32F0 these Channels are mapped to pins as follows 0:7 as A0:A7, 8:9 as B0:B1, and 10:15 as C0:C5. Internal channel 16 is the temperature, and 17 the VREF.

• Analog output: Channel 1.

• Hardware Events:

  • Blue Push Button 1 (PA0) with two events:
    • button pressed - flag(1), and
    • button depressed - flag(2)

• sleep, tic/toc:

  through SysTick_Handler() which counts in 1ms increments through interrupts

• Serial Port

  requires an additional USB/TTL cable (UART2 using PA2/PA3 on the discovery board)

Firmware footprint with all features enabled and 8 demo scripts (bytes): 37872 flash, 548 data and 3940 bss.