Here is a list of issues of the TI emulations in MAME which need further investigation.
Media
- Writing to HFE disks is disabled
- Cassette output may be unreadable by a real TI (waveform)
Peripheral devices
- SCSI block mode DMA does not work
TI-99/8
Problems with DSDD disks
Description: In some situations, DSDD disks are not readable with the HX5102. File operations return a device error. In other situations, the same images do work properly.
Analysis: The reason is that the i8272A disk controller falsely detects an FM IDAM on a MFM track. Of course, the following CRC check will fail, but this incident is reported as a broken header instead of a wrong density. The false detection depends on the starting point of time for that track; for this reason, it sometimes works. The problem is that the handler in the ROM only evaluates this to "no mark found" if none of the other conditions are met. Concretely, if there is no proper mark found, the CRC flag must not be set. It may also indicate a bug in the handler routine of the HX5102.
Fix: The behavior of the i8272A could be modified to reset all flags except MA in case there is no header found. This must be verified with other protection schemes.
Alternative: Do not use DSDD floppy disks with the HX5102.
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