Friday, April 17, 2020

Kernel of Truth

I spent some time today trying to get NitrOS-9 booting on the CMS 9619 SBC. I was able to get this working in emulation, so I was hopeful that it would be an easy job with real hardware. After some minor modifications to deal with timing in the slower environment, the ZMODEM module is working perfectly! However, getting NitrOS-9 running has been much more complicated.

As part of the boot process, NitrOS-9 relocates the kernel "disk" sectors from $2600 to high memory. Memory was cheap with my 6809 emulator, so everything that is not ROM was configured as RAM. The emulator easily relocated the kernel to $C000-$Dxxx, just below the main debug ROM at $E000-$FFFF. On my real board, that address range is not populated with RAM, so, I was relocating the kernel into thin air! I changed the load area to $7000-$8xxx, but had a problem because the relocation routines expect the video buffer at $8000, and over-write part of the kernel. I could keep toying with the relocation routines, but I think I just need to get more SRAM to populate the empty ROM sockets. I just put an order in, and am hoping for for some new 8K SRAM ICs by the end of next week.

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