various IEC optimizations

c64/kernal/iec/iec_rx_check_eoi.s

@@ -7,17 +7,20 @@ iec_rx_check_eoi:
 
 	// 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
+	// Loop iteraction takes 11 cycles, 19 full iterations are enough
 
-	ldx #$11                           // 2 cycles
+	ldx #$13                           // 2 cycles
 
 !:
-	lda CIA2_PRA                       // 4 cycles
-	rol                                // 2 cycles, to put CLK in as the last bit
-	bpl iec_rx_check_eoi_done          // 2 cycles if not jumped
+	bit CIA2_PRA                       // 4 cycles
+	bvc iec_rx_check_eoi_done          // 2 cycles if not jumped
 	dex                                // 2 cycles
     bne !-                             // 3 cycles if jumped
-    
+
+    // FALLTROUGH
+
+iec_rx_check_eoi_confirm:
+
 	// 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

c64/kernal/iec_fast/iec_fast_common.s

@@ -7,10 +7,9 @@
 #if (CONFIG_IEC_JIFFYDOS || CONFIG_IEC_DOLPHINDOS) && !CONFIG_MEMORY_MODEL_60K
 
 
-iec_update_EAL_by_Y:
+iec_update_EAL_by_Y: // note: Carry has to be set by caller!
 
 	tya
-	sec
 	adc EAL+0
 	sta EAL+0
 	bcc !+

c64/kernal/iec_fast/load_dolphindos.s

@@ -13,16 +13,15 @@ load_dolphindos:
 	sei
 
 	// A trick to shorten EAL update time
-	ldy #$FF
+	ldy #$00
 
 	// FALLTROUGH
 
 load_dolphindos_loop:
 
 	// Check if this was EOI
-	lda IOSTATUS
-	and #K_STS_EOI
-	bne load_dolphindos_end
+	bit IOSTATUS
+	bvs load_dolphindos_end
 
 	// Wait for the talker to release the CLK line
 !:
@@ -34,9 +33,9 @@ load_dolphindos_loop:
 	and #$FF - BIT_CIA2_PRA_DAT_OUT    // release
 	sta CIA2_PRA
 
-	// Wait till data line is released (someone else might be holding it)
+	// Wait till DATA line is released (someone else might be holding it)
 !:
-	lda CIA2_PRA
+	bit CIA2_PRA
 	bpl !-
 
 	// Check if EOI - routine can damage .X, but this is safe
@@ -44,7 +43,6 @@ load_dolphindos_loop:
 
 	// Retrieve and store byte
 	lda CIA2_PRB
-	iny
 	sta (EAL),y
 
 	// Pull DATA to acknowledge
@@ -53,7 +51,7 @@ load_dolphindos_loop:
 	sta CIA2_PRA
 
 	// Handle EAL
-	cpy #$FF
+	iny
 	bne load_dolphindos_loop
 	inc EAL+1
 	jmp load_dolphindos_loop
@@ -61,6 +59,7 @@ load_dolphindos_loop:
 load_dolphindos_end:
 
 	// Update EAL
+	clc
 	jsr iec_update_EAL_by_Y
 
 	// End of load loop

c64/kernal/iec_fast/load_jiffydos.s

@@ -132,6 +132,7 @@ load_jiffydos_end:
 	tax
 
 	// Update EAL
+	sec
 	jsr iec_update_EAL_by_Y
 
 	// Indicate that no byte waits in output buffer