From: Bart <bart-jeroen@hemstra.com>
Date: Mon, 30 Jan 2017 16:06:02 +0000 (+0100)
Subject: Update trsload80.s to work on real hardware
X-Git-Url: https://git.ndcode.org/public/gitweb.cgi?a=commitdiff_plain;h=c238eabf028aa20ff765b0f71c12b47f3258d0d0;p=FUZIX.git

Update trsload80.s to work on real hardware

In order to run Fuzix on a real TRS-80 Model 4 some corrections have to be made to the bootloader:
- The correct mode was not selected, Video Page #1 needs to be selected. The emulator SDLTRS does not behave correctly; on a real Model 4 Video Page #0 starts on FC00 with a distorted screen as result. So: OUT (0x84),#0x86 is working correctly.
- Stackpointer out of the way on 0xEE00, doesn't overwrite code.
- The ctc6845 registers are not loaded correctly, they must be read in reverse order. So INC HL must be DEC HL and the label must be put at the end of the table.
- The Clear Screen routine was not implemented correctly.
- On a real Model 4 a formatted floppy must be used to boot. This will be a SDDD disk, 40 tracks, formatted for TRS-DOS 6 or LS-DOS 6. These formatted disks have 18 sectors per track, starting on sector 0 and ending on 17. So an extra DEC A is used and a test against sector 18 instead of 19.

With these changes the bootloader is still 256 bytes and now works on SDLTRS and on a real Model 4 128K. A real or virtual formatted floppy is necessary, so the instructions need an update as well.
---

diff --git a/Kernel/platform-trs80/trs80load.s b/Kernel/platform-trs80/trs80load.s
index c9437f90..f1f613d0 100644
--- a/Kernel/platform-trs80/trs80load.s
+++ b/Kernel/platform-trs80/trs80load.s
@@ -2,10 +2,11 @@
 ;
 ;	TRS80 bootblock (256 bytes)
 ;
-;	    .org #0x0
+.area	    BOOT	(ABS)
+.org	    0x000
 start:
-	    ld a, #0x06			; kernel map, 80 column, no remap
-	    out (0x84), a
+	    ld a, #0x86			; kernel map, 80 column, no remap
+	    out (0x84), a		; video page 1
 	    ld a, #0x50			; 80 column, sound, altchars off,
 					; ext I/O on , 4MHz
 	    out (0xEC), a
@@ -49,27 +50,26 @@ flopstat:
 fail:	    jr fail
 ;
 go:   
-	    ld sp, #floppy_read
+	    ld sp, #0xEE00		; temp stackpointer
 
             ; load the 6845 parameters
-	    ld hl, #_ctc6845
-	    ld bc, #1588
-ctcloop:    out (c), b			; register
+	    ld hl, #_ctc6845		; reverse order
+	    ld bc, #0x0F88
+ctcloop:    out (c), b			; select register
 	    ld a, (hl)
-	    out (0x89), a		; data
-	    inc hl
+	    out (0x89), a		; output data
+	    dec hl
 	    djnz ctcloop
 
    	    ; clear screen
 	    ld hl, #0xF800
-	    inc hl
 	    ld de, #0xF801
-	    ld bc, #1999
+	    ld bc, #0x07FF
 	    ld (hl), #' '
 	    ldir
 	    ld de, #0xF800
 	    call prints
-	    .ascii 'TRS80Load 0.1\0'
+	    .ascii 'TRS80Load 0.2\0'
 
 	    ld hl, #0x0100
 ;
@@ -102,12 +102,13 @@ seekstat:
 	    .ascii 'seek\0'
 bad:	    jr bad
 secmove:    xor a
+	    dec a	
 	    ld (secnum), a
 nextsec:
 	    ld a, (secnum)
 	    inc a
 	    ld (secnum), a
-	    cp #19
+	    cp #18
 	    jr z, lastsec
 	    push hl
 	    call floppy_read
@@ -117,7 +118,7 @@ nextsec:
 
 tracknum:   .db 28			; tracks 29-39 (50688 bytes)
 
-_ctc6845:				; registers in reverse order
+				; ctc6845 registers in reverse order
 	    .db 99
 	    .db 80
 	    .db 85
@@ -132,9 +133,8 @@ _ctc6845:				; registers in reverse order
 	    .db 9
 	    .db 0
 	    .db 0
-	    .db 0
-; recycle last crc value as secnum so we fit 256 bytes
-secnum:	    .db 0
+secnum:	    .db 0		; recycle last crc value as secnum so we fit 256 bytes
+_ctc6845:   .db 0
 
 
 prints: