I've been banging my head against a wall for a couple of weeks now, on and off, so I'm hoping some kind person here can point me in the right direction 
My goal: get a sample program building from source and running on a Saturn emulator, so I can start feeling my way around a working program, iterating changes and learning about the Saturn bit by bit.
(Running on real HW would be fine too, but from what I can tell that is more difficult for a beginner given lack of available tools.)
My main target at first is graphics, so anything that puts pixels on the screen will do, maybe with some basic controller input for parameter tweaking.
Where I'm at right now: I can build the SBL and SGL sample programs no problem, but I cannot get them to run in an emulator. I have actually failed to get *anything* that is not part of a pre-built ISO to run in an emulator.
Since I'm not sure where I'm going wrong, I will describe in as much detail as I can below how I got to this point.
I'm not attached to getting these specific samples to run, anything will do I guess! I just chose them since they were official, seemed to be well documented, and used standard build tools. I've downloaded a bunch of homebrew samples too, but all the ones I've found so far looked like they would send me down a rabbit hole of using ancient windows binaries of dubious origin which I was keen to resist if at all possible...
My background: programmer with experience in various languages and environments, including C/C++ on a variety of platforms, but no embedded experience - I'm used to having the linker magically produce an executable and having the OS run it for me!
Environment: Linux using GNU toolchain, and Yabause or Mednafen as the emulator.
(I would consider switching to Windows if the tooling is much better, although all my Windows experience is MSVC rather than GNU tools.)
What I have done so far:
1) Built sh-elf GNU tools using this thread as a guide: Building your own toolchains
I used GCC 9.3.0, and Binutils 2.34, in addition to the old `gasp` asm-preprocessor from Binutils 2.12 needed by SEGA's `gasm` script.
When set up to do Saturn dev, my PATH includes an sh-elf symlinks dir looking something like this:
(There's more, but I abbreviated the list for clarity)
gasm.sh is SBL's GASM.BAT converted to bash, it seems to be working fine.
With this setup, most SEGA Makefile seem to work out of the box without modifications.
2) Built SBL samples
I downloaded SBL601.ZIP from antime.kapsi.fi and built some samples with the above tools using the sample's provided Makefile.
The linker complained about 'ambiguous object format' of the pre-built .a files under segalib/lib, but that was easily fixed with `objcopy -O elf32-sh in.a out.a && mv out.a in.a`, after which there were no problems.
Depending on the the sample, I now have a game.cof file, and in the case of game_cd, a game.bin file.
The .cof file is sometimes actually an ELF depending on the specific sample, but whatever - objcopy detects the format correctly regardless of extension.
3) Make a disc image
I've done this two ways:
a) produce a BIN/CUE for SBL's game_cd sample, because that includes CD audio.
b) produce an ISO containing the game.bin file for other more self-contained samples, using a mkiso command I found on this forum.
I'll go through both.
3.a) Try to run SBL game_cd via BIN/CUE
Run `make` inside the game_cd directory. This produces a game.bin file.
Strangely for SBL samples, but not for SGL samples, the `objcopy -O binary` command used to produce the game.bin file outputs padding prior to the actual code at the 0x06010000 start address, so the game.bin file itself is 97mb of mostly junk.
I worked around this with `dd if=game.bin of=game.new bs=1 skip=100728832 && mv game.new game.bin` to chop off the first 0x6010000 bytes, and the resulting game.bin file now looks similar other non-inflated .bin files from other samples.
Ok, so now to turn this into a CD image.
First, I copied segasmp/sys/ip_gnu.bin to ip.bin in the game_cd directory. I don't 100% understand the IP.BIN format yet, but I understand from the docs that this one is for use with the samples. I have tried with both the provided binary, and a binary rebuilt from source. I have confirmed that the ip.bin contains the correct start address.
Then I opened Dosbox and used VCDTOOLS:
vcdbuild.exe game.scr
This produces GAME.DSK and GAME.RTI.
I then used CyberwarriorX's tool to turn this into a CUE/BIN:
stripvcd.exe game.rti -o cd.bin
If I load this CUE/BIN in either emulator, it shows the SEGA logo, goes to a black screen, and hangs.
In Yabause if I open the debugger, the master SH2 always seems to be executing at an address that corresponds to a function _SND_ChgMap in the game binary, which seems to be SBL internals (appears in segalib binaries).
I do not know SH2 ASM (or indeed any ASM!), so I can't really follow what it is doing, but it does not look like much. (I was looking forward to learning SH2 as part of this project, but I'd rather start on working code to be honest...)
(It's worth noting I guess that even if I did get this process to work, it's way too involved for any kind of reasonable iteration cycle... I guess I might be able to automate it?)
3.b) Try to run a bin-only sample via ISO
I've tried this on numerous samples such as several under segasmp/sblsgl, or segasmp/spr, and samples from the SGL libraries such as samples/akira or demos/biplane.
Build steps are the same as above, and to make the ISO I use this command:
(Note that SGL ip.bin differs from SBL sample ip.bin, so that part of the command changes.)
Loading this results in a brief pause, and then bailing to the BIOS CD player screen, with a 'start application' button that repeats the process.
I have sucessfully used this genisoimage command to reproduce a working image from an existing ISO I found - i.e. I extracted the ip.bin from the ISO, and copied the files out, and then re-built a new ISO from the files and the ip.bin. That worked, so it's probably not a problem with the command above but rather the files I am feeding into it?
Anyway... I could keep grinding on this for a while I'm sure, but I'm almost out of energy at this point. Does anyone have any pointers for me?
Please let me know if I'm down totally the wrong path - thanks!
My goal: get a sample program building from source and running on a Saturn emulator, so I can start feeling my way around a working program, iterating changes and learning about the Saturn bit by bit.
(Running on real HW would be fine too, but from what I can tell that is more difficult for a beginner given lack of available tools.)
My main target at first is graphics, so anything that puts pixels on the screen will do, maybe with some basic controller input for parameter tweaking.
Where I'm at right now: I can build the SBL and SGL sample programs no problem, but I cannot get them to run in an emulator. I have actually failed to get *anything* that is not part of a pre-built ISO to run in an emulator.
Since I'm not sure where I'm going wrong, I will describe in as much detail as I can below how I got to this point.
I'm not attached to getting these specific samples to run, anything will do I guess! I just chose them since they were official, seemed to be well documented, and used standard build tools. I've downloaded a bunch of homebrew samples too, but all the ones I've found so far looked like they would send me down a rabbit hole of using ancient windows binaries of dubious origin which I was keen to resist if at all possible...
My background: programmer with experience in various languages and environments, including C/C++ on a variety of platforms, but no embedded experience - I'm used to having the linker magically produce an executable and having the OS run it for me!
Environment: Linux using GNU toolchain, and Yabause or Mednafen as the emulator.
(I would consider switching to Windows if the tooling is much better, although all my Windows experience is MSVC rather than GNU tools.)
What I have done so far:
1) Built sh-elf GNU tools using this thread as a guide: Building your own toolchains
I used GCC 9.3.0, and Binutils 2.34, in addition to the old `gasp` asm-preprocessor from Binutils 2.12 needed by SEGA's `gasm` script.
When set up to do Saturn dev, my PATH includes an sh-elf symlinks dir looking something like this:
Code:
as -> ../bin/sh-elf-as
gasm -> ../../libs/SBL6/segalib/awk/gasm.sh
gasp -> ../../binutils-2.12/bin/sh-elf-gasp
gcc -> ../bin/sh-elf-gcc
ld -> ../bin/sh-elf-ld
objcopy -> ../bin/sh-elf-objcopy
objdump -> ../bin/sh-elf-objdump(There's more, but I abbreviated the list for clarity)
gasm.sh is SBL's GASM.BAT converted to bash, it seems to be working fine.
With this setup, most SEGA Makefile seem to work out of the box without modifications.
2) Built SBL samples
I downloaded SBL601.ZIP from antime.kapsi.fi and built some samples with the above tools using the sample's provided Makefile.
The linker complained about 'ambiguous object format' of the pre-built .a files under segalib/lib, but that was easily fixed with `objcopy -O elf32-sh in.a out.a && mv out.a in.a`, after which there were no problems.
Depending on the the sample, I now have a game.cof file, and in the case of game_cd, a game.bin file.
The .cof file is sometimes actually an ELF depending on the specific sample, but whatever - objcopy detects the format correctly regardless of extension.
3) Make a disc image
I've done this two ways:
a) produce a BIN/CUE for SBL's game_cd sample, because that includes CD audio.
b) produce an ISO containing the game.bin file for other more self-contained samples, using a mkiso command I found on this forum.
I'll go through both.
3.a) Try to run SBL game_cd via BIN/CUE
Run `make` inside the game_cd directory. This produces a game.bin file.
Strangely for SBL samples, but not for SGL samples, the `objcopy -O binary` command used to produce the game.bin file outputs padding prior to the actual code at the 0x06010000 start address, so the game.bin file itself is 97mb of mostly junk.
I worked around this with `dd if=game.bin of=game.new bs=1 skip=100728832 && mv game.new game.bin` to chop off the first 0x6010000 bytes, and the resulting game.bin file now looks similar other non-inflated .bin files from other samples.
Ok, so now to turn this into a CD image.
First, I copied segasmp/sys/ip_gnu.bin to ip.bin in the game_cd directory. I don't 100% understand the IP.BIN format yet, but I understand from the docs that this one is for use with the samples. I have tried with both the provided binary, and a binary rebuilt from source. I have confirmed that the ip.bin contains the correct start address.
Then I opened Dosbox and used VCDTOOLS:
vcdbuild.exe game.scr
This produces GAME.DSK and GAME.RTI.
I then used CyberwarriorX's tool to turn this into a CUE/BIN:
stripvcd.exe game.rti -o cd.bin
If I load this CUE/BIN in either emulator, it shows the SEGA logo, goes to a black screen, and hangs.
In Yabause if I open the debugger, the master SH2 always seems to be executing at an address that corresponds to a function _SND_ChgMap in the game binary, which seems to be SBL internals (appears in segalib binaries).
I do not know SH2 ASM (or indeed any ASM!), so I can't really follow what it is doing, but it does not look like much. (I was looking forward to learning SH2 as part of this project, but I'd rather start on working code to be honest...)
(It's worth noting I guess that even if I did get this process to work, it's way too involved for any kind of reasonable iteration cycle... I guess I might be able to automate it?)
3.b) Try to run a bin-only sample via ISO
I've tried this on numerous samples such as several under segasmp/sblsgl, or segasmp/spr, and samples from the SGL libraries such as samples/akira or demos/biplane.
Build steps are the same as above, and to make the ISO I use this command:
Code:
genisoimage -sysid "SEGA SATURN" -volid "volumeid" -volset "volumeset" -publisher "SEGA ENTERPRISES, LTD." -preparer "SEGA ENTERPRISES, LTD." -appid "applicationid" -generic-boot ../../sys/ip_gnu.bin -full-iso9660-filenames -o OUT.ISO game.bin(Note that SGL ip.bin differs from SBL sample ip.bin, so that part of the command changes.)
Loading this results in a brief pause, and then bailing to the BIOS CD player screen, with a 'start application' button that repeats the process.
I have sucessfully used this genisoimage command to reproduce a working image from an existing ISO I found - i.e. I extracted the ip.bin from the ISO, and copied the files out, and then re-built a new ISO from the files and the ip.bin. That worked, so it's probably not a problem with the command above but rather the files I am feeding into it?
Anyway... I could keep grinding on this for a while I'm sure, but I'm almost out of energy at this point. Does anyone have any pointers for me?
Please let me know if I'm down totally the wrong path - thanks!
