Summary

Makes CS4231 indirect register 23 read-only. The datasheet for the CS4231 (non-A, which is what 86Box emulates) marks this as a reserved register and the Linux OSS ad1848.c WSS driver relies on this register being read-only to correctly detect the codec type and set the sample rate for audio playback. This fixes digital audio playback on CS4231-based sound cards (such as the OPTi 929/AcerMagic S20 and Yamaha YMF-701) on Mandrake Linux 8.0 (kernel 2.4.3).

Checklist

• Closes #xxx
• I have discussed this with core contributors already
• This pull request requires changes to the ROM set
  • I have opened a roms pull request - https://github.com/86Box/roms/pull/changeme/

References

Provide links to datasheets or other documentation that helped you implement this pull request.

• Crystal CS4231 datasheet: http://www.datasheet.hk/view_download.php?id=1629286&file=0316%5Ccs4231-kq_1442620.pdf
• Linux ad1848.c WSS driver: https://android.googlesource.com/kernel/msm/+/android-o-preview-4_r0.6/sound/oss/ad1848.c