Hi John,
The notes I took at the time are at the bottom [1] and go into some
detail. I've split out the main points below, so hopefully the full
notes will be clearer.
The key point is that variables defined in the flash dictionary when the
svn RISC-V AmForth is assembled (using the assembler macro you found)
work just fine. A dictionary entry for the variable is created in flash
and points to a correctly allocated area of memory in RAM.
Variables defined at the prompt are different. They use the colon word
"variable" to dynamically generate the dictionary header and allocate
the RAM required. At this point the RISC-V svn code is storing the
dictionary entry in RAM, and is allocating the memory required for the
variable from that same "block" of RAM. The existing codebase colon
definition for variable is not set up for this. Because of this, a store
! to the variable defined at the prompt overwrites part of the
dictionary header in RAM, corrupting the dictionary, which when
accessed, results, in this case, with a hang.
There are ways to deal with this, one option is explored in the link.
There are others. I wanted to highlight some of the issues/choices
associated with dictionary storage and RAM allocation.
Best wishes,
Tristan
[1] https://tjnw.co.uk/amforth-rv/20231107/20231107.html
On 2026-01-05 22:28, John Sarabacha wrote:
when a X @ sequence is entered after
$AABBCCDD X !
The interpreter may do a XT_EXECUTE so if
$AABBCCDD is on tos x3 register
CODEWORD "execute",EXECUTE
mv x17,x3
loadtos
j DO_EXECUTE
this would spell trouble and give an exception, and the worst part is
the
loadtos would
hide the problem because now x17 is propagating an unexecutable code
address being on a byte boundary and a stack dump is not going to show
this
(.s)
This may have been planned as a feature to support the execution of
code in
ram
This is starting to make sense.
John S
On Mon, Jan 5, 2026 at 4:05 PM John Sarabacha <[email protected]>
wrote:
Hi Tristan,
I tried this sequence on ESP32Forth and there were no issues.
in RISCV
>> variable X
>> creates the structure below in ram
.macro VARIABLE Name, Label
HEADER Flag_visible|Flag_variable, "\Name", \Label, PFA_DOVARIABLE
.word rampointer
.set rampointer, rampointer+4
.endm
>> $AABBCCDD X !
>> rampointer (above) is where the address where $AABBCCDD is stored
CODEWORD "!", STORE # ( x 32-addr -- ) --> ( $AABBCCDD rampointer-X
-- )
lw x5, 0(x4) x5 (temp reg) is loaded with
rampointer-X from 0(x4) by indexing x4 (Data Stack Pointer)
sw x5, 0(x3) ramponter -X is written to ram
location
pointed by address in tos (x3)
lw x3, 4(x4) x3 tos is loaded from 4(x4)
indexing of
x4 (now has initial value $AABBCCDD )
addi x4, x4, 8 Data Stack Pointer is incremented by
8
NEXT
This is not behaving as it's description ( x 32-addr -- ) this segment
of
code is leaving $AABBCCDD on tos x3 register
whether this is part of the problem ???
Regards,
John S
On Mon, Jan 5, 2026 at 3:28 PM <[email protected]> wrote:
Hi John,
Here is the sequence of words working correctly. The results
would be similar for any 32 bit Forth. Try it on ESP32Forth.
|S| 1|hex
|S| 2|variable x
|S| 3|x u.
|O| 3|20000950
|S| 4|aabbccdd x !
|S| 5|x @ u.
|O| 5|AABBCCDD
|W| 6|
There is no writing to or reading from a misaligned address,
so whilst it can be a major issue, it is not the issue here.
The issue with with the svn repo code is as described in the
link. I wanted to mention it as it will raise some questions
about about flash/ram and dictionary/variable storage that I
wish I had considered earlier than I did. It seemed a good
moment given that Martin had just got a prompt on the UNO R4.
Best wishes,
Tristan
On 2026-01-05 17:36, John Sarabacha wrote:
> AmForth is doing exactly what it is told to do, looks like the code
> base is
> functional, the processor (Cortex-M4/RISCV) is doing what it is
> supposed to
> do. It is up to the user to supply the correct information otherwise
> the
> processor will complain (exception out).
>
> On Mon, Jan 5, 2026 at 12:27 PM John Sarabacha <[email protected]>
> wrote:
>
>> The other possibility is that it is not a valid address that the
>> processor
>> can access which could cause an exception
>>
>> On Mon, Jan 5, 2026 at 12:18 PM John Sarabacha <[email protected]>
>> wrote:
>>
>>> So when you execute X @ you are trying to indirectly read from the
>>> address 0xAABBCCDD
>>> which could cause an exception
>>>
>>> On Mon, Jan 5, 2026 at 12:08 PM Martin Kobetic <[email protected]>
>>> wrote:
>>>
>>>> On Mon, Jan 5, 2026 at 11:51 AM John Sarabacha
>>>> <[email protected]>
>>>> wrote:
>>>>
>>>> > Still learning forth , programmed in many other languages (alot of
>>>> > assembler)
>>>> > variable X
>>>> > $AABBCCDD X !
>>>> > X @
>>>> >
>>>> > However tell me if I am wrong, you are creating a variable
definition
>>>> for X
>>>> > you are setting this variable X to the address $AABBCCDD and then
>>>> trying to
>>>> > read a value from this
>>>> > address on to the tos.
>>>>
>>>>
>>>> Almost. The second line is storing value 0xAABBCCDD at the address
>>>> represented by variable X.
>>>> It is the word `variable` in previous line that allocates memory for
>>>> the
>>>> variable and associates the corresponding
>>>> address with a new word `X` that simply pushes that address onto the
>>>> stack
>>>> when executed.
>>>>
>>>> In the test run I quoted above
>>>> ---
>>>> > X
>>>> ok
>>>> > .s
>>>> 5 200002B8 200002C4 200002A8 20000288 8 ok
>>>> ---
>>>> The address represented by the variable was 0x200002B8, so it was
>>>> 8-byte
>>>> aligned, so should be ok alignment-wise.
>>>> But your hypothesis with alignment issues seems definitely worth
>>>> checking
>>>> out as well.
>>>>
>>>> Your warning about the fault interrupts is certainly worth heeding,
>>>> I
>>>> don't
>>>> think we do much there on the ARM side.
>>>> Another thing to follow up on.
>>>>
>>>> _______________________________________________
>>>> Amforth-devel mailing list for http://amforth.sf.net/
>>>> [email protected]
>>>> https://lists.sourceforge.net/lists/listinfo/amforth-devel
>>>>
>>>
>
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