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Re: BBC Tube WIP [Re: Pernod] #117135 04/10/20 01:52 AM
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Pernod Offline OP
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Currently working on the Millipede Prisma3 device, which was mainly used to add graphics to TV productions.
http://www.computinghistory.org.uk/det/44086/Millipede-Electronics-Prisma-3/
http://chrisacorns.computinghistory.org.uk/32bit_UpgradesH2Z/Millipede_Prisma3.html

It's built around the HD63484 ACRTC which is not yet fully emulated, so am having to delve into the missing commands. So far I've been adding interrupts and the DMA commands and it's now able to load graphics screens (from Winchester) directly into the frame buffer.
[Linked Image from i.imgur.com]
It's supposed to be 256 colours but haven't yet looked at the palette.

An issue I'm having with the HD63484 is that it executes commands too fast. The DMA transfer from the BBC is flaky as it's constantly polling the HD63484 status register checking the Write FIFO Empty bit, but can miss changes as there's no delay between adding data to the FIFO and the FIFO being emptied when written to the frame buffer. The ACRTC manual contains cycle counts for each command, so want to add some kind of timer that I can call with a cycle count to add delays. Any suggestions/examples?


BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.
Re: BBC Tube WIP [Re: Pernod] #117148 04/13/20 11:56 AM
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Pernod Offline OP
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Fixed a bug in DMA transfer mode, and implemented the palette:
[Linked Image from i.imgur.com]
Used by BBC Wales for their Christmas 1987 logo:
[Linked Image from i.imgur.com]

Last edited by Pernod; 04/13/20 12:13 PM.

BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.
Re: BBC Tube WIP [Re: Pernod] #117154 04/13/20 02:42 PM
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rfka01 Offline
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Wow! What's the resolution and number of concurrent colours on this?


NCR DMV- DEC Rainbow- Siemens PCD- ITT 3030-Oly People- Acorn A5000- Olivetti M20
Re: BBC Tube WIP [Re: rfka01] #117155 04/13/20 03:09 PM
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Pernod Offline OP
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Originally Posted by rfka01
Wow! What's the resolution and number of concurrent colours on this?

768x576 with 256 colours.


BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.
Re: BBC Tube WIP [Re: Pernod] #117348 05/19/20 07:25 PM
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Pernod Offline OP
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The bbc machines have seriously lost performance over time, no idea when.

My benchmarks with mame 0.221 -bench 10 on an i7-4770K @3.5GHz are:
bbcmarm 110% (BBC Master, ARM co-processor, SCSI Winchester)
bbcmt 163% (BBC Master, 65C102 co-processor)
bbcm512 297% (BBC Master, 80186 co-processor, Mouse)
bbcb 338% (BBC Model B)
bbcm 383% (BBC Master)
electron 1643% (Electron)

I'm currently working on a clone consisting of BBC Master, 65C102 co-processor, SCSI Winchester, Mouse, Prisma Graphics (Hitachi HD63484) and I'm down to about 80%.

My only thought is the amount of expansion interfaces added over the years, especially the 1mhzbus where devices can be chained so jumping through trampolines.

Can anyone suggest anything I can do to get some performance back, or help pinpoint when performance dropped?

Regarding the chained 1mhzbus devices I was wondering if it would be better to implement device_memory_interface in bbc_1mhzbus_slot_device and let each device install it's handlers into a single address_map, which would save jumping through trampolines between chained devices.

Even bbcb and bbcm with no attached devices are slow compared to electron, so must be something else I can do. Any suggestions?


BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.
Re: BBC Tube WIP [Re: Pernod] #117349 05/19/20 08:19 PM
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R. Belmont Offline
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Are bbcb/bbcm doing any funky banking? If so, converting them to use bankdev would likely gain some performance.

Re: BBC Tube WIP [Re: R. Belmont] #117350 05/19/20 09:06 PM
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Tafoid Offline
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I ran a compilation of my speed outputs from my 10 seconds regression tests over nearly the last 2 years. I'll be honest, the machine I tested BBCM largely stayed within the mid/upper 300% speed range (i5 3.2ghz). Minor variations + or - are likely due to me using my in use local computer for all testing and other tasks may affect speeds slightly. I've linked a report BBCM Speed

It may help to check your devices one by one and see what is slowing things down. You have a LOT going showing in the -listdevices output. ELECTRON machine isn't using nearly as many devices when compared.

Re: BBC Tube WIP [Re: Pernod] #117351 05/19/20 09:19 PM
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Pernod Offline OP
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I already use bankdev, but could maybe make more use of it.

Maybe things slowed down when I added bbc_internal_slot_device to cater for internal expansion boards that can take over any of the address space. This meant all ram/rom now jumps through a trampoline to see whether an installed internal expansion board should be paged into a region, not sure what I can do to improve this.

I'll see if Tafoid fancies trying to pinpoint the performance drops.


BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.
Re: BBC Tube WIP [Re: Pernod] #117461 06/23/20 07:23 PM
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Pernod Offline OP
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Another modern co-processor I'm working on, running an ARM7 at 64MHz, see http://www.sprow.co.uk/bbc/armcopro.htm
[Linked Image from i.imgur.com]
This is currently bringing performance down to about 50%, but not surprising in this case.


BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.
Re: BBC Tube WIP [Re: Pernod] #117462 06/23/20 08:24 PM
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R. Belmont Offline
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64 MHz certainly isn't going to do the performance any favors until we get an ARM DRC, but it's still cool to see it running.

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