MSaarna: Created page with "

 ; X-Board Description ; The X-board (iet7830) is an internal expansion board for the ATARI 7800 which ; gives the system 128 Kbyte of SRAM and one POKEY chip. ; ; The ex..."

2015-11-07T23:44:35Z

Created page with "<pre> ; X-Board Description ; The X-board (iet7830) is an internal expansion board for the ATARI 7800 which ; gives the system 128 Kbyte of SRAM and one POKEY chip. ; ; The ex..."

New page

<pre>
; X-Board Description
; The X-board (iet7830) is an internal expansion board for the ATARI 7800 which
; gives the system 128 Kbyte of SRAM and one POKEY chip.
;
; The expansion SRAM is located from $4000 up to $7fff and is divided into 8 banks
; of 16Kbyte each. The SRAM is by default disabled when the system starts up and
; has to be enabled by the application. This is so that existing games and software
; will function properly. To enable the SRAM write a "1" to Bit 3 of the XCTRL
; register.
;
; The POKEY is located in the high section of the available memory area at $0400
; of the 7800. It is selected from $0460 - $046f when Bit 4 of the XCTRL register
; is set to "1" if Bit 4 = "0" the POKEY is disabled.
;
XCTRL = $0470 ; Note Write only
; Bit 4 = Enable POKEY chip
; Bit 3 = Enable Banked 128Kbyte SRAM
; Bit 2 = Bit 2 of SRAM bank select
; Bit 1 = Bit 1 of SRAM bank select
; Bit 0 = Bit 0 of SRAM bank select

;
; Bit patterns for enabling/disabling XBoard features.
XENABLEMEM = %00001000
XENABLEPOKEY = %00010000

XPOKEYBASE1 = $0450
XPOKEYBASE2 = $0460

MEMTESTCOUNT = 10 ; Number of iterations when testing the XBoard Memory
XMEMORYSTART = $4000 ; This is where the memory of the XBoard starts

;************************************************************************
;*
;* Function: SetXCtrl
;*
;* Description: This function sets the XCTRL register to the value in
;* acc and updates the shadow
;*
;************************************************************************
SetXCtrl: sta XCTRL
sta XCTRL_SHDW

rts
;************************************************************************
;*
;* Here's the code for checking and enabling the XBoard SRAM
;*
;* This test fills the entire 16K memory bank with a known pattern
;* and then compares it with the same pattern. If any byte is unequal
;* the memory test aborts and reports no memory.
;*
;* For this test to be effective the length of the test pattern must
;* not be equal to a power of 2 base. So it has been chosen to just
;* repeat all strings used into memory.
;*
;************************************************************************
; First we load the memory with a known test string......
lda #XENABLEMEM
jsr SetXCtrl ; Enable XBOARD SRAM and set to bank zero

lda #<XMEMORYSTART
sta MemTest
lda #>XMEMORYSTART
sta MemTest+1 ; Loads the memory address

lda #MEMTESTCOUNT ; Number of iterations to test in memory (<256)
sta Iterate

ldy #0
XCheck0:
ldx #<MEMTESTLEN ; Load memory test string length (<256)
XCheck1:
lda Text1,X
sta (MemTest),Y ; Store test character

inc MemTest
bne XCheck15
inc MemTest + 1 ; Increment the XBoard memory pointer

XCheck15:
lda MemTest ; Check low target adress for zero
bne XCheck2 ; Skip if not zero

lda MemTest + 1 ; Check high target address
cmp #$80 ; If it's hex 80 we have a wrap = done
bne XCheck2 ; Loop again if not zero
jmp XCheck25 ; Break out of this loop

XCheck2: dex
bne XCheck1 ; Store the entire test data set
beq XCheck0 ; Reload test string counter

; Second phase of the memory test
; Now we compare the stored data in memory with the reference content....
XCheck25:
lda #<XMEMORYSTART
sta MemTest
lda #>XMEMORYSTART
sta MemTest+1 ; Loads the memory address

lda #MEMTESTCOUNT ; Number of iterations to test in memory (<256)
sta Iterate

ldy #0
XCheck3:
ldx #<MEMTESTLEN ; Load memory test string length (<256)
XCheck4:
lda Text1,X ; Load the known data to compare memory contents with
cmp (MemTest),Y ; And do the comparison.
bne XCheck6 ; Skip further checking if not equal, ie. memory error

XCheck7: inc MemTest ; ... otherwise continue to compare.
bne XCheck5
inc MemTest + 1 ; Increment the XBoard memory pointer
XCheck5:
lda MemTest ; Check low target adress for zero
bne XCheck55 ; Skip if not zero

lda MemTest + 1 ; Check high target address
cmp #$80 ; If it's hex 80 we have a wrap = done
bne XCheck55 ; Loop again if not zero
jmp TA1 ; Break out of this loop
XCheck55:
dex
bne XCheck4 ; Store the entire test data set
beq XCheck3 ; And reload the test length counter

TA1: jsr XMemOK ; Go show memory indicator
</pre>

XBoard Memory Init - Revision history

MSaarna: Created page with "
; X-Board Description ; The X-board (iet7830) is an internal expansion board for the ATARI 7800 which ; gives the system 128 Kbyte of SRAM and one POKEY chip. ; ; The ex..."