From 44a951f09c68ba417fc2a1894ab9cfcdf45b2258 Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Thu, 26 Dec 2019 14:15:57 +0100
Subject: [PATCH] initial DolphinDOS byte reception, seems to work

---
 c64/kernal/iec/iec_rx_byte.s                 |  4 +-
 c64/kernal/iec_fast/iec_rx_byte_dolphindos.s | 48 +++++++++++++++++++-
 2 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/c64/kernal/iec/iec_rx_byte.s b/c64/kernal/iec/iec_rx_byte.s
index 5297a4ae..fe5e7068 100644
--- a/c64/kernal/iec/iec_rx_byte.s
+++ b/c64/kernal/iec/iec_rx_byte.s
@@ -24,7 +24,7 @@ iec_rx_byte:
 	jsr iec_wait_for_clk_release
 
 	// We then release the DATA to signal we are ready
-	// We can use this routine, since we weren't pulling CLK anyway
+	// We can use this routine, since we were not pulling CLK anyway
 	jsr iec_release_clk_data
 
 	// Wait till data line is released (someone else might be holding it)
@@ -68,7 +68,7 @@ iec_rx_bit_loop:
 	jsr iec_wait_for_clk_release
 
 	// (we do this implicitly below, with a tighter routine,
-	// so that we don't have timing problems, as the requirements
+	// so that we do not have timing problems, as the requirements
 	// are quite tight. Basically we need to read the clock and data
 	// bit from the same byte read.
 
diff --git a/c64/kernal/iec_fast/iec_rx_byte_dolphindos.s b/c64/kernal/iec_fast/iec_rx_byte_dolphindos.s
index 97a908ab..54828900 100644
--- a/c64/kernal/iec_fast/iec_rx_byte_dolphindos.s
+++ b/c64/kernal/iec_fast/iec_rx_byte_dolphindos.s
@@ -7,9 +7,55 @@
 #if CONFIG_IEC_DOLPHINDOS
 
 
+// XXX experimental, partially copied from standard protocol, not fully tested yet!
+// XXX maybe this can be integrated into iec_rx_byte???
+
+
 iec_rx_byte_dolphindos:
 
-	panic #$00 // XXX implement this
+	// Store .X and .Y on the stack - preserve them
+	phx_trash_a
+	phy_trash_a
 
+	// First, we wait for the talker to release the CLK line
+	jsr iec_wait_for_clk_release
+
+	// We then release the DATA to signal we are ready
+	// We can use this routine, since we were not pulling CLK anyway
+	jsr iec_release_clk_data
+
+	// Wait for talker to pull CLK.
+	// If over 200 usec (205 cycles on NTSC machine) , then it is EOI.
+	// Loop iteraction takes 13 cycles, 17 full iterations are enough
+
+	ldx #$11                // 2 cycles
+iec_rx_dd_clk_wait1:
+	lda CIA2_PRA            // 4 cycles
+	rol                     // 2 cycles, to put CLK in as the last bit
+	bpl iec_rx_dd_not_eoi   // 2 cycles if not jumped
+	dex                     // 2 cycles
+    bne iec_rx_dd_clk_wait1 // 3 cycles if jumped
+    
+	// Timeout - either this is the last byte of stream, or the stream is empty at all.
+	// Mark end of stream in IOSTATUS
+	jsr kernalstatus_EOI
+
+iec_rx_dd_not_empty:
+
+	// Pull data for 60 usec to confirm it
+	jsr iec_release_clk_pull_data
+	jsr iec_wait60us
+	jsr iec_release_clk_data
+
+iec_rx_dd_not_eoi:
+
+	// Retrieve byte via parallel, store it
+	lda CIA2_PRB
+	sta TBTCNT // $A4 is a byte buffer according to http://sta.c64.org/cbm64mem.html
+
+	// Inform the drive about byte reception
+	jsr iec_release_clk_pull_data
+
+	jmp iec_rx_end
 
 #endif