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- ; RP2040 PIO program for accelerating SCSI initiator / host function
- ;
- ; Copyright (c) 2022 Rabbit Hole Computing™
- ;
- ; Run "pioasm scsi_accel_host.pio scsi_accel_host.pio.h" to regenerate the C header from this.
- ; GPIO mapping:
- ; - 0-7: DB0-DB7
- ; - 8: DBP
- ; Side set is ACK pin
- .define REQ 19
- .define ACK 26
- ; Read from SCSI bus using asynchronous handshake.
- ; Data is returned as 16-bit words that contain the 8 data bits + 1 parity bit.
- ; Number of bytes to receive minus 1 should be written to TX fifo.
- ; Number of bytes to receive must be divisible by 2.
- .program scsi_host_async_read
- .side_set 1
- pull block side 1 ; Get number of bytes to receive
- mov x, osr side 1 ; Store to counter X
- start:
- wait 0 gpio REQ side 1 ; Wait for REQ low
- nop [1] side 1 ; Wait for signals to settle
- in pins, 9 side 0 ; Assert ACK, read GPIO
- in null, 7 side 0 ; Padding bits
- wait 1 gpio REQ side 0 ; Wait for REQ high
- jmp x-- start side 1 ; Deassert ACK, decrement byte count and jump to start
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