Transtech Transputer, User Manual

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Host Computer Interface
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Transputer Motherboard User Manual TMB M 711
To allow an interrupt on any of these sources write a ‘1’ to the
relevant bit position. To inhibit an interrupt on any of these sources
write a ‘0’ to the relevant bit position.
Once the PC has been interrupted the interrupt handler must
determine the source of the interrupt. This can be done by reading
the Input/OutputStatusRegisters, the Error register and the status
registers on the DMA controller chip.
3.4.5 DMA & Interrupt Channels
There is a small degree of flexibility in terms of the interrupt channel
and DMA channel that can be used within the PC: the DMA channel
can be set to 1 or 2 and the interrupt channel can be set to 3 or 6.
DMA channel 1 is often used by ethernet or other networking cards.
DMA channel 2 is used by the PC to communicate with the floppy
disk controller. It is possible to share DMA channel 2 with the floppy
disk controller by careful programming of the floppy disk controller
enable flag located at IO address space #3F2. Whenever a floppy
disk access is about to take place the BIOS always enables location
#3F2. Hence to use DMA channel 2, the software must disable the
controller (by writing a zero to the enable flag) and enable its own
drivers. At the end of the DMA transfer the software must disable its
own drivers.
The floppy disk subsystem also uses interrupt channel 6. The floppy
disk uses this interrupt channel to notify the PC that it is inactive and
as such the PC can switch off the “in use” lamp on the front panel.
The interrupt is generated about two seconds after the last disk
access. Any software using this interrupt channel, should be able to
handle such interrupts (or be able to guarantee that such interrupts
cannot arrive).
End of DMA Transputer Link data Link data
bit 0 bit 1 bit 2 bit 3
transfer error input ready output ready
Figure 29. Interrupt control mask register