I've made some progress:
- multiplexer controller first cut vhdl written and partially simulated
- memory chip fitted and tested in both BeebFPGA and minimal Blitter firmwares
- some multiplexer chips fitted: video syncs now coming from core
- fitted all the video connectors
- fitted i2c extension connector (used temporarily as a ps/2 connector with BeebFPGA)
The memory thing took a while to get going. I couldn't get it working in BeebFPGA (it was getting stuck in the bootloader at step 11) so I wrote a memory soak tester on the minimal firmware which was good because it showed up a solder bridge. But still beebfpga didn't boot. I finally twigged that I had data out and data in mixed up - this has tripped me up before...is it data out of the ram or data out of the fpga...![:oops:]( "Embarassed")
The multiplexer testing is pretty slow - going. I'm developing the controller and testing piecemeal - there's always the possibility that if I get the controller wrong the various chips on the bus could start fighting and get hot. So far it's looking pretty promising.
I have just done a few shots of the different analogue (15kHz) colour options:
RGB
This is pretty crisp as would be expected and shows no colour artefacts.
S-video
Still pretty crisp some patterning on the vertical bars - due I think to the way the colour sub-carrier is generated. Still pretty good.
Baseband PAL
As expected, less crisp, but still pretty good. The patterning is a bit worse but not objectionable in real life.
The photos make the patterning look worse than in reality.
All in all the generated PAL carrier seems to work well enough, better than I'd expected when I first thought of the 1-bit video stuff. It certainly looks crisper and less noisy than the beeb, plus we can have NULA colours on PAL/S-Video which aren't available on the original Beeb+NULA. Plus it's nice to be able to run all these outputs together RGB+PAL+S-video+MONO all at once - hopefully HDMI too soon.
Firmware
I've been developing two firmwares in parallel. One is a hacked about version of BeebFPGA, which is great as I can dive in with a fully functional system from the word go. The second is a cut-down version of the Blitter firmware, which is very modular, which allows me to easily reconfigure it to test individual subsystems as I go.
At present the "Blitter" firmware is really minimal:
- a 6502 system running
- uart (using the RVDebugger)
- 2K ROM containing a NoIce monitor
- a 8K of FPGA block RAM for zero page/stack and small programs
- the rest of RAM &1000 - &7FFF from the motherboard SRAM
- JIM window and paging registers to access the whole RAM address space via FD00-FDFF
This was a help in testing the SRAM - I ported a command line RAM tester and quickly diagnosed a solder bridge between two address lines.
D
- multiplexer controller first cut vhdl written and partially simulated
- memory chip fitted and tested in both BeebFPGA and minimal Blitter firmwares
- some multiplexer chips fitted: video syncs now coming from core
- fitted all the video connectors
- fitted i2c extension connector (used temporarily as a ps/2 connector with BeebFPGA)
The memory thing took a while to get going. I couldn't get it working in BeebFPGA (it was getting stuck in the bootloader at step 11) so I wrote a memory soak tester on the minimal firmware which was good because it showed up a solder bridge. But still beebfpga didn't boot. I finally twigged that I had data out and data in mixed up - this has tripped me up before...is it data out of the ram or data out of the fpga...
The multiplexer testing is pretty slow - going. I'm developing the controller and testing piecemeal - there's always the possibility that if I get the controller wrong the various chips on the bus could start fighting and get hot. So far it's looking pretty promising.
I have just done a few shots of the different analogue (15kHz) colour options:
RGB
This is pretty crisp as would be expected and shows no colour artefacts.
S-video
Still pretty crisp some patterning on the vertical bars - due I think to the way the colour sub-carrier is generated. Still pretty good.
Baseband PAL
As expected, less crisp, but still pretty good. The patterning is a bit worse but not objectionable in real life.
The photos make the patterning look worse than in reality.
All in all the generated PAL carrier seems to work well enough, better than I'd expected when I first thought of the 1-bit video stuff. It certainly looks crisper and less noisy than the beeb, plus we can have NULA colours on PAL/S-Video which aren't available on the original Beeb+NULA. Plus it's nice to be able to run all these outputs together RGB+PAL+S-video+MONO all at once - hopefully HDMI too soon.
Firmware
I've been developing two firmwares in parallel. One is a hacked about version of BeebFPGA, which is great as I can dive in with a fully functional system from the word go. The second is a cut-down version of the Blitter firmware, which is very modular, which allows me to easily reconfigure it to test individual subsystems as I go.
At present the "Blitter" firmware is really minimal:
- a 6502 system running
- uart (using the RVDebugger)
- 2K ROM containing a NoIce monitor
- a 8K of FPGA block RAM for zero page/stack and small programs
- the rest of RAM &1000 - &7FFF from the motherboard SRAM
- JIM window and paging registers to access the whole RAM address space via FD00-FDFF
This was a help in testing the SRAM - I ported a command line RAM tester and quickly diagnosed a solder bridge between two address lines.
D
Statistics: Posted by dominicbeesley — Thu Jun 12, 2025 12:32 am