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STATUS
command codes = 8 and 10
ES:BX pointer to a request header. Format:
length field
This driver must perform the following:
A) perform the requested function
B) set the busy bit
C) set the status word in the request header.
For input on character devices: if the busy bit is 1 on return, a
write request would wait for completion of a current request. If
the busy bit is 0, there is no current request. Therefore, a
write request would start immediately.
For input on character devices with a buffer: if the busy bit is
1 on return, a read request does to the physical device. If the
busy bit is 0, there are characters in the device buffer and a
read returns quickly. It also indicates that a user has typed
something. DOS assumes all character devices have a type-ahead
input buffer. Devices that do not have this buffer should always
return busy=0 so that DOS does not hang waiting for information
to be put in a buffer that does not exist. |