UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Gemini 80-Bus System

JohnBHanson · 15th Sep 2019, 3:53 am

Adding READ ADDRESS command broke early gemini bios versions (eg 1.4).

The problem was the bios issued a READ ADDRESS and just polled the BUSY flag
in the status register to see if the command had completed. It *did not* read the
floppy disk controller data register to recover the data from the READ ADDRESS command. Because of this the emulator did not complete the READ ADDRESS command as the data had not been read by the Z80.

Changed the code so that after 100 reads of the status register without reading the data register the FDC BUSY flag is cleared if it is set.

Yet another version - very sorry.

15th Sep 2019, 3:53 am	#216
JohnBHanson Heptode Join Date: Aug 2009 Location: Worthing, Sussex, UK. Posts: 661	Re: Gemini 80-Bus System Adding READ ADDRESS command broke early gemini bios versions (eg 1.4). The problem was the bios issued a READ ADDRESS and just polled the BUSY flag in the status register to see if the command had completed. It did not read the floppy disk controller data register to recover the data from the READ ADDRESS command. Because of this the emulator did not complete the READ ADDRESS command as the data had not been read by the Z80. Changed the code so that after 100 reads of the status register without reading the data register the FDC BUSY flag is cleared if it is set. Yet another version - very sorry.