From 062c73a80979405260d323e4b86d28b177cbbe10 Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Mon, 8 Mar 2021 21:47:51 +0100
Subject: [PATCH] initial (very primitive) general sector caching

---
 src/dos_m65/dos_init.s                        | 26 +++++++++++++-----
 .../filesystem_cbm/fs_cbm_nextdirentry.s      | 27 +++++--------------
 src/dos_m65/lowlevel/lowlevel_readsector.s    | 24 ++++++++++++++++-
 3 files changed, 49 insertions(+), 28 deletions(-)

diff --git a/src/dos_m65/dos_init.s b/src/dos_m65/dos_init.s
index 85b48e5c..f4c5c5d3 100644
--- a/src/dos_m65/dos_init.s
+++ b/src/dos_m65/dos_init.s
@@ -39,20 +39,28 @@ dos_INIT:
 	sta IDX1_TALKER
 	sta IDX2_TALKER
 
-	; Initialize device handlers
+	; Initialize buffer metadata
 
-	jsr unit_sd_init
-	jsr unit_fd_init
-	jsr unit_rd_init
+	lda #$0
+	ldx #17
+@2:
+	sta BUFTAB_TRACK, x
+	dec
+	sta BUFTAB_UNIT, x
+	sta BUFTAB_DEV, x
+	sta BUFTAB_SECTOR, x
+	inc
+	dex
+	bpl @2
 
 	; Initialize DMA list
 
 	ldy #$08
-@2:
+@3:
 	lda dos_dmalist_template, y
 	sta DMAJOB_LIST, y
 	dey
-	bpl @2:
+	bpl @3:
 
 	; Initialize helper code in RAM
 
@@ -70,6 +78,12 @@ dos_INIT:
 	sta code_RTS_03
 	sta code_RTS_04
 
+	; Initialize device handlers
+
+	jsr unit_sd_init
+	jsr unit_fd_init
+	jsr unit_rd_init
+
 	; Safer version of 'dos_EXIT' - does not affect speed related registers
 
 	clc
diff --git a/src/dos_m65/filesystem_cbm/fs_cbm_nextdirentry.s b/src/dos_m65/filesystem_cbm/fs_cbm_nextdirentry.s
index fc500dac..e53ee21e 100644
--- a/src/dos_m65/filesystem_cbm/fs_cbm_nextdirentry.s
+++ b/src/dos_m65/filesystem_cbm/fs_cbm_nextdirentry.s
@@ -78,7 +78,7 @@ fs_cbm_nextdirentry:
 	clc
 	rts
 
-@get_sector_lo:
+@get_sector_lo:              ; processing the 1st half of the buffer finished
 
 	; Check if this was the last sector
 
@@ -88,31 +88,16 @@ fs_cbm_nextdirentry:
 	cmp #$FF
 	beq @end_of_dir
 
-	; Transition from 1st half of the buffer, to (possibly) the second one
+	; Load the next sector
 	
 	lda SHARED_BUF_1+0
-	cmp BUFTAB_TRACK+1
-	bne @get_sector_lo_next
-
-	lda SHARED_BUF_1+1	
-	dec
-	cmp BUFTAB_SECTOR+1
-	bne @get_sector_lo_next
-
-	; It's OK, we can transition to the upper half of the buffer
-
-	lda FD_DIRENT
-	jmp @cont
-
-@get_sector_lo_next:
-
-	lda SHARED_BUF_1+0
-	sta PAR_TRACK
+	sta PAR_TRACK	
 	lda SHARED_BUF_1+1
 	sta PAR_SECTOR
+
 	bra @get_sector_common
 
-@get_sector_hi:
+@get_sector_hi:              ; processing the 2nd half of the buffer finished
 
 	; Check if this was the last sector
 
@@ -122,7 +107,7 @@ fs_cbm_nextdirentry:
 	cmp #$FF
 	beq @end_of_dir
 
-	; Load new sector
+	; Load the next sector
 
 	lda SHARED_BUF_1+$100+0
 	sta PAR_TRACK
diff --git a/src/dos_m65/lowlevel/lowlevel_readsector.s b/src/dos_m65/lowlevel/lowlevel_readsector.s
index c75e23ca..fc180823 100644
--- a/src/dos_m65/lowlevel/lowlevel_readsector.s
+++ b/src/dos_m65/lowlevel/lowlevel_readsector.s
@@ -1,9 +1,31 @@
 
-; Read a single sector from a block device
+; Read a sector pair from a block device
 
 
 lowlevel_readsector:
 
+	; XXX compare device and unit too
+
+	; Check if buffer contains data from given track
+
+	lda PAR_TRACK
+	cmp BUFTAB_TRACK+1
+	bne lowlevel_readsector_force
+ 
+	; Check if sectors match
+
+	lda PAR_SECTOR
+	and #%11111110
+	cmp BUFTAB_SECTOR+1
+	bne lowlevel_readsector_force
+
+	; Data already loaded into buffer - do nothing
+
+	clc
+	rts
+
+lowlevel_readsector_force:
+
 	; Select FDD sector as buffer
 
 	lda #%10000000                     ; select floppy buffer