SNA support broken ?

[FabLafarge]

Loading a SNA file seems broken at the moment. The CPC just sits at the usual BASIC prompt instead of running the snapshot.

[DSkywalk]

Tested on lastest retroarch/core (standalone 1.10.0/cap32 - 4.5.2 b8f09a0) and working as expected :+1:

[FabLafarge]

Tested again, doesn't work here :

Steps to reproduce :

• Download fresh binaries from: https://buildbot.libretro.com/stable/1.10.0/windows/x86_64/RetroArch.7z
• Load core -> Download a core -> Amstrad - CPC/GX4000 (Caprice32) (ie ver 4.5.2 b8f09a0)
• Load content -> Browse and select any SNA file (ie Fruity Frank :) )
• Expected result : CPC emulation started, SNA file loaded and running (ie game running)
• Actual result : usual BASIC 1.1 prompt, waiting for user interaction

Reproduced on Windows and PSPVita builds.

[FabLafarge]

Further investigation seems to indicate SNA support may be incomplete

Enabling verbose logging and attempting to load produces the following log :

SNA Error (18): C:\Temp\Fruity Frank.sna (0)=1
 (1)=1

which would indicate this error: ERR_SNA_SIZE

This particular snapshot is 47.110 bytes in size, which would indicate some kind of compression. This file is valid with other emulators such as CPCEC.

I imagine SNA loading works fine with snapshots generated by the core itself, but will often fail with third party SNAs fetched off the internet.

[FabLafarge]

Had a dive into the code, and my findings so far are :

• In cap32.h, that "+1" violates the SNA fileformat specs (see https://www.cpcwiki.eu/index.php/Format:SNA_snapshot_file_format ) , which means all subsequent data is offset by 1. Therefore, this core is only compatible with its own SNA and will fail with any SNA created with a third party emulator.

typedef struct {
   char id[8+1];
   char unused1[8];
   unsigned char version;

• RAM data compression is indeed unsupported which in itself is not a violation of the specs, but severly limits the amount of third party SNAs that could be loaded if the previous bug were fixed.

[FabLafarge]

Good news: I made a build changing this

typedef struct {
   char id[8+1];
   char unused1[8];
   unsigned char version;

to this

typedef struct {
   char id[8+1];
   char unused1[7];
   unsigned char version;

and the core now loads successfully thirdparty uncompressed snapshots :)

[DSkywalk]

We may have to make an old SNA converter, but it can be prepared as a contrib with a small python script. I prefer your solution and that the SNA is as the format that was decided as standard. Thank you very much.