U1MB PORTB bits configuration.

[greblus]

Hello.

 

Is there any documentation explaining how to use PORTB in different memory configurations of the Ultimate 1MB extension?

[flashjazzcat]

The upgrades in U1MB correspond to and are compatible with Compy-Shop 320KB, 576KB, and standard 1MB expansions. These are described in section 3.5 of the Altirra Hardware Reference Manual.

[greblus]

Thanks FJC, I wasn't aware that Altirra's docs are so complete. But it doesn't tell clearly how to use it.

 

I remember that there was a simple formula for 130xe bank switching: 129+mode*16+bank*4

where bits 2-3 defined bank number and bits 4-5 the mode.

 

Now let's say for a 320kb rambo: if both Antic and CPU are on all the time, does it mean that mode will be always 0

and bank is switched simply by setting portb a value of 129+bank*4?

 

For 576k and 1088k modes it must be a bit more complicated

[greblus]

Ok, found this in Atari Magazine and the explanation from chapter 3.5 of Altirra

manual seems clear now:

 

Memory Location 54017 (130XE Only)

 

Bit Position Function

0

If 1, enable OS ROM, disable RAM from $C000-$FFFF (default)

If 0, disable OS ROM, enable RAM from $C000-$FFFF

1

If 0, enable BASIC ROM at $A000-$BFFF (default)*

If 1, disable BASIC ROM, enable RAM at $A000-$BFFF

2-3

If 00 (decimal 0), switch first 16K bank of extra 64K into $4000-$7FFF

If 01 (decimal 4), switch second 16K bank of extra 64K into $4000-$7FFF

If 10 (decimal , switch third 16K bank of extra 64K into $4000-$7FFF

If 11 (decimal 12), switch fourth 16K bank of extra 64K into $4000-$7FFF

4

If 1, deny 6502 access to extra bank (default)

If 0, allow 6502 access to extra bank

5

If 1, deny ANTIC access to extra bank (default)

If 0, allow ANTIC access to extra bank

6

Not presently used. Default = 1

7

If 1, disable self-test ROM, enable RAM at $5000-$57FF (default after powerup)

If 0, enable self-test ROM, disable RAM at $5000-$57FF

 

But if I understand correctly, there is no mode available in U1MB where Antic

has access to banked memory? Do I get it right?

Edited February 5, 2013 by greblus

[greblus]

Ok, I got it wrong (many times ) but found one good explanation of all memory upgrades in polish:

 

www.atari.apox.pl/art,47,rozszerzenia-pamieci.html

 

(host is down, got it from google cache)

 

So below is my interpretation followed an example in Action.

 

Atari memory extensions:

 

PORT B it's a group of memory extensions based and named after $d301 PORTB control register. These extensions work with 16kb switchable banks mapped in the address area $4000-$7fff, same as in Axlon extension.

 

* 130XE - in standard configuration Atari 130XE has 4 additional banks, selectable using bits 2 and 3 of the PORT B register. If bit 4 is set to 0 6502 will have access to the additional bank, if bit 4 is set to 1 CPU will access main memory. Bit 5 is controlling access of the Antic processor, thus an independent access of 6502 or Antic is possible.

 

* 192kB - extension similar to 130XE described above, but the bank number is defined by bits 2, 3 and 6, so up to 8 banks can be selected (what means +128kB of banked memory)

 

* TOMS 256kB, 256kB/ 320kB RAMBO - in this extension bit 4 controls access of both 6502 and Antic at the same time. Bit 5 is an additional bit allowing to select banks, so bits 2,3,5 and 6 make 16 banks available (+256kB RAM).

 

* 576kB RAMBO/320kB Compy Shop - in these extensions bit 7 which was normally used to enable or disable Self Test plays a double role: if bit 4 is set to 1 it works as in stock configuration. If set to 0 it is an additional bit used for bank selection, so bits 2,3,6,7 allow to select 16 banks, in case of RAMBO 576kB bit 5 was another bit used for bank selection, what resulted in 32 banks available and finally in Compy Shop bit 5 allows to control Antic access.

 

* 1088kB RAMBO/576kB Compy Shop - extensions similar to 576kB RAMBO/320kB Compy Shop but there is an additional bit 1 used for banks selection if bit 4 is set to 0 (if bit 4 = 1 bit 1 works as in stock config). Bits 1, 7, 6, 2, 3, 5 are used for selection of one of 32 banks (+512kB) in 576kB Compy Shop.

 

Now very simple (and suboptimal) Action! example: writing 10 bytes with bank number to first 10 banks of Rambo 320kb extension, hope it makes it even clearer:

 

; 7 6 5 4 3 2 1 0 bit no

;

; 1 0 0 0 0 0 1 1 : 131

; 1 0 0 0 0 1 1 1 : 135

; 1 0 0 0 1 0 1 1 : 139

; 1 0 0 0 1 1 1 1 : 143

; 1 0 1 0 0 0 1 1 : 163

; 1 0 1 0 0 1 1 1 : 167

; 1 0 1 0 1 0 1 1 : 171

; 1 0 1 0 1 1 1 1 : 175

; 1 1 0 0 0 0 1 1 : 195

; 1 1 0 0 1 0 1 1 : 203

 

; bits 2356 define bank no, bit 4 allows CPU and ANTIC access

 

proc main()

 

byte array pb = [131 135 139 143 163 167 171 175 195 203]

 

card portb=54017

int i,j

byte pointer ptr

 

for i=0 to 9 do

portb=pb(i)

ptr=$4000

for j=0 to 9 do

ptr^=i

ptr==+1

od

od

 

for i=0 to 9 do

portb=pb(i)

ptr=$4000

printf("Bank %I%E", i)

for j=0 to 9 do

printf("%I", ptr^)

ptr==+1

od

printe()

od

 

do od

return

 

 

[flashjazzcat]

Excellent work. I thought some of the usual suspects might have stepped in here, but you've presented some useful information off the back of your own investigations.