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; =============================================================================
; net.asm - raw link-port serial for networking (bypasses the console/terminal).
;
; The Game Boy link port is one 8-bit shift register. These two calls move a
; byte at a time: ssend transmits with the GB as clock master; srecv waits for
; a byte with the GB as slave (external clock), yielding while it blocks. On top
; of these, userland runs SLIP framing and talks to a host-side gateway.
;
; The LCD terminal + on-screen keyboard mean the console no longer needs the
; link port, so it is free to be the network.
; =============================================================================
INCLUDE "include/gbos.inc"
SECTION "net", ROM0
; sys_ssend(E = byte) - transmit one byte (GB drives the clock).
sys_ssend::
ld a, e
ld [rSB], a
ld a, $81 ; start transfer, internal clock
ld [rSC], a
.wait
ld a, [rSC]
bit 7, a
jr nz, .wait ; bit7 clears when the byte has shifted out
ret
; sys_srecv() -> A = received byte. GB is the slave; blocks (yields) until the
; peer clocks a byte in.
sys_srecv::
.poll
ld a, $80 ; start transfer, external clock (receive)
ld [rSC], a
ld a, [rSC]
bit 7, a
jr z, .got ; bit7 clear => a byte arrived
call SchedYield
jr .poll
.got
ld a, [rSB]
ret
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