gnupic: PIC14e: HIGH directive not setting bit-7
Subject:
Re: PIC14e: HIGH directive not setting bit-7
From:
Borut ####@####.####
Date:
30 Jul 2013 06:18:32 -0000
Message-Id: <51F75A78.2040502@gmail.com>
Hi Richard,
this really seems to be a gputils bug: I tried your example with MPASMX
and HIGH sets the 7th bit:
0000 00003 testme:
0000 3080 00004 movlw HIGH table
0001 0085 00005 movwf FSR0H
0002 3004 00006 movlw LOW table
0003 0084 00007 movwf FSR0L
00008
0004 345A 00009 table dt 0x5a
00010 end
Please create a new ticket at https://sourceforge.net/p/gputils/bugs/.
Borut
On 30. 07. 2013 02:58, Richard Hodges wrote:
> I am writing new code for the 16F1518, and I believe that gpasm is not handling HIGH
> correctly for this chip. My datasheet (DS41452C) states on page 19:
>
> "3.1.1.2 Indirect Read with FSR
> The program memory can be accessed as data by setting bit 7 of the FSRxH register and
> reading the matching INDFx register. The MOVIW instruction will place the lower eight bits
> of the addressed word in the W register. Writes to the program memory cannot be performed
> via the INDF registers. Instructions that access the program memory via the FSR require
> one extra instruction cycle to complete. Example 3-2 demonstrates accessing the program
> memory via an FSR.
> The HIGH directive will set bit<7> if a label points to a location in program memory."
>
> I _think_ that this access method is only for the "enhanced" 14 bit chips (like the
> 12f1822 and 12f1501, for example.) But I could be wrong...
>
> This may be the line in question: (line 250 of gpasm/evaluate.c)
> case HIGH:
> return (evaluate(p->value.unop.p0) >> 8) & 0xff;
>
> I looked at disassembled relocatable code from gplink and I do not see the high bits set
> there either.
>
> Here is code to show what happens:
> LIST P=PIC16F1518
> include p16f1518.inc
> testme:
> movlw HIGH table
> movwf FSR0H
> movlw LOW table
> movwf FSR0L
>
> table dt 0x5a
> end
>
> And here is the disassembly:
>> gpdasm -p 16f1518 bad.hex
> 000000: 3000 movlw 0
> 000001: 0085 movwf 0x5
> 000002: 3004 movlw 0x4
> 000003: 0084 movwf 0x4
> 000004: 345a retlw 0x5a
>
> I do not know whether the struct pnode has enough information to figure out when to set
> the high bit (bit 7) of the result, but I can dig into it if it is not an easy fix for the
> main developers.
>
> Thanks!
> -Richard
