Surely set would only work if I had an unsigned offset from the
beginning of a table? I'm using a signed offset from the middle of a
table.
On 20 May 2008, at 19:48, Edwin Blink wrote:
1)
Normally the value is &FF and it looks pretty stable too considering
PRO-DOS uses IM 2 without a vector table. So your choices are IM 0/
IM 1 both do a RST 38H or IM 2 which 'calls' the adress found at the
address pointed by I register (MSB) and the value on the databus
(LSB). Like the speccy there may be some hardware connected that
changes the default value on the databus so a 257 byte vector table
is recomended.
2)
If choose to put all the LSB at 32768 followed by the MSB then you
could use the following:
set 7,h
ld e,(hl)
set 3,h
ld d,(hl)
Other usefull addresses for the table would be 16384 (use SET 6,H),
8192 (SET 5,H), 4096 (SET 4,H) or 0 (you don't need the first SET
instruction at all)
Edwin
----- Original Message ----- From: "Thomas Harte" <[EMAIL PROTECTED]
>
To: <sam-users@nvg.ntnu.no>
Sent: Tuesday, May 20, 2008 3:03 PM
Subject: Short, short questions
I'm about to finish my lunch break, sorry if I sound slightly
short...
1) is there any pattern or logic to the values placed on the bus
during interrupts? I guess an equivalent question is: what realistic
options do I have on the Sam for catching and processing interrupts?
2) are there any non-obvious tricks for fast access to a table
containing 16bit words, indexed by an 11bit (signed) integer? At the
minute I'm essentially doing:
[stuff to work out offset into table in hl]
ld bc, <address of middle of table - which is aligned to a two-byte
boundary>
add hl, hl
add hl, bc
ld e, (hl)
inc l
ld d, (hl)
