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Tube: tube_get

[Elite-A, I/O processor]

Name: tube_get [Show more] Type: Subroutine Category: Tube Summary: As the I/O processor, fetch a byte that's been sent over the Tube from the parasite Deep dive: Tube communication in Elite-A
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * CHPR calls tube_get * DET1 calls tube_get * DIL2 calls tube_get * DILX calls tube_get * draw_blob calls tube_get * draw_tail calls tube_get * HA2 calls tube_get * HANGER calls tube_get * HLOIN calls tube_get * LOIN (Part 1 of 7) calls tube_get * MSBAR calls tube_get * PIXEL calls tube_get * scan_xin calls tube_get * scan_y calls tube_get * write_0346 calls tube_get * write_fe4e calls tube_get * write_pod calls tube_get

Tube communication in Elite-A uses the following protocol: Parasite -> I/O processor * Uses the FIFO 1 status and data registers to transmit the data * The parasite calls tube_write to send a byte to the I/O processor * The I/O processor calls tube_get to receive that byte from the parasite I/O processor -> Parasite * Uses the FIFO 2 status and data registers to transmit the data * The I/O processor calls tube_put to send a byte to the parasite * The parasite calls tube_read to receive that byte from the I/O processor This routine is called by the I/O processor to receive a byte from the parasite. The code is identical to Acorn's MOS routine that runs on the parasite to implement OSWRCH across the Tube.
.tube_get BIT tube_r1s \ Check whether FIFO 1 has received a byte from the \ parasite (which it will have sent by calling its own \ tube_write routine). We do this by checking bit 7 of \ the FIFO 1 status register NOP \ Pause while the register is checked BPL tube_get \ If FIFO 1 has received a byte then bit 7 of the status \ register will be set, so this loops back to tube_get \ until FIFO 1 contains the byte transmitted from the \ parasite LDA tube_r1d \ Fetch the transmitted byte by reading the FIFO 1 data \ register into A RTS \ Return from the subroutine