mos6507's Blog - Chimera update

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Earlier in the week we were able to verify that Supercharger games are working again. I haven't tried any multiloads other than Survival Island, but odds are, we're good to go on that front.

 

Next, we've been able to get bidirectional serial communications working. We wrote a test program that lets you type characters in Hyperterminal and have them echo back after reaching the VCS.

 

Next, we were able to get queues working again (I don't think I'll call queues Ouroboros anymore, it's too hard to type). Right now queues appear to work when running out of ARM RAM. We're limited to only 16 of these (4K total). Tomorrow we're scheduled to test queues out of cart SRAM, where timing is much tighter. The current hotspot memory map we're using supports 100 SRAM queues, hence 25.6K bytes, but we have 64K to work with. So ultimately we may adjust how the hotspots operate. We want to limit the hotspots to the last page of cart RAM so as not to steal away too much space from code.

 

Also, we were having some problems with RF interference with the serial cable connected. Through some serendipity we were able to solve this problem by enabling a resistor pack component that is on the cart between the VCS and the CPLD. We hope that this part should both help protect the cartridge from getting fried by bad VCS code and also enable alternate ways of writing RAM.

 

The most recent demo written has 4 queues running at once providing playfield bitmaps. Two represent the first iteration of PF1, for graphics and color. The third represents the background color underneath the second iteration of PF1. The last is the second iteration of PF1 graphics. In addition to mirroring text back out to Hyperterminal, I poke the data into that last queue. The VCS has no trouble keeping up with incoming keypresses during VBLANK. We're currently running at 38.4K baud. I expect us to eventually be able to bump this up to 56K. We also have to implement hardware flow control.

 

For those whom seeing is believing:

 

Chimera Demo 1

 

Here is what the kernel code looks like for this demo. Pretty simple, huh?

 

CODE

StartKernel

; Set PF Pattern

sta WSYNC

 

;lda #%10101010

;sta PF1

;sta PF2

 

; Count Kernel Lines

ldy #KERNH

KernelLoop

 

 

lda CH_QUEUE_FAST

sta PF1

 

lda CH_QUEUE_FAST+1

sta COLUPF

SLEEP 21

 

lda #00

sta COLUPF

 

lda CH_QUEUE_FAST+2

sta PF1

 

lda CH_QUEUE_FAST+3

sta COLUBK

 

 

SLEEP 8

lda #00

sta COLUBK

 

 

sta WSYNC

dey

bne KernelLoop

 

; Clear PF Pattern

sty PF0

sty PF1

sty PF2

 

EndKernel

 

 

 

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