io.txt

every ass needs to fart sometimes. memory-mapped io is ideal for this.

when this ass needs to print text, it uses a device called TEXT0.
consult the isa reference for which system register to access to
retrieve the address of TEXT0. memory operations on TEXT0 have
the following semantics:

TEXT0[0]: opcode. read == 0, write == 1
TEXT0[1]: length in bytes
TEXT0[2]: pointer
TEXT0[3]: status. bit 0 = busy, bit 1 = transaction pending

When TEXT0[0] is written to, the other fields are read and a transaction 
is initiated and the busy bit is set.

If a transaction is already in progress, the pending bit will be set 
and the request is ignored.

After the transaction is complete, bit 0 will be cleared.
It is the responsibility of the user code to wait for the
busy bit to become 0 and re-submit the opcode if the
pending bit is set, and clear it.