From: Jon Langseth <jon.langseth@ntnu.no>
Date: Wed, 8 Feb 2017 19:27:48 +0000 (+0100)
Subject: An experiment in reading files on CP/M
X-Git-Url: https://git.defcon.no/?a=commitdiff_plain;h=HEAD;p=z80cpm

An experiment in reading files on CP/M
---

diff --git a/rf1.asm b/rf1.asm
new file mode 100644
index 0000000..f30699d
--- /dev/null
+++ b/rf1.asm
@@ -0,0 +1,129 @@
+; rf1.asm - Read File experiment #1
+; ASM dialect is for crasm/z80, producing Intel HEX.
+;
+; Attempting to understand file read operations on CP/M2
+; Reference material:
+; http://www.cpm.z80.de/manuals/archive/cpm22htm/ch5.htm
+; The default FCB can be used, it's location is at 05CH
+; The default DMA buffer can be used, it's located at 080H
+; When CCP jumps to 0100H, it's already taken the two
+; first parameters to the command, and placed them in
+; the default FCB area. More on this later in the code
+; CCP has also placed the parameter string in the default
+; DMA buffer area (080H). Not used in this experiment.
+
+; crasm macros.. Z80 CPU type, iHEX output, readable listing pages, listing-toggles..
+CPU Z80
+OUTPUT HEX
+PAGE 24,120
+LIST ON
+CLIST ON
+ILIST ON
+MLIST ON
+
+; BDOS call constants..
+conout	EQU 2		; Console output, put 1 char from E to Console
+strout	EQU 9		; String output, place string at (DE) terminated by $ to Console
+openf	EQU 15		; Open file, using the FCB at address (DE)
+reads	EQU 20		; Read sequential, get next DMABUF from file at FCB in (DE)
+closef	EQU 16		; Close file, using hte FCB at (DE)
+bdos	EQU 5		; Call jump-address for all BDOS calls.
+
+; Standard location constants..
+sfcb	EQU 0x5c	; The Standard/default FCB
+fcbcr	EQU sfcb+32	; The CR field of the FCB
+sdma	EQU 0x80	; The Standard/default DMA Buffer
+
+; Other fun constants...
+eof	EQU 0x1a	; CP/M EOF character, 0x1Ah/26d
+
+; Origin at TPA Start, 0x100
+* = 0x100
+
+	; Start by printing out the filename currently in the default FCB.
+	; CCP will take 'command file.sfx file1.sfx" and fill the default
+	; FCB appropriately for file.sfx, plus the needed content for a
+	; second FCB started at 0x6c (default fcb + 10h)
+	; The Drive index is the first byte, and the filename is 8+3 bytes
+	LD HL, sfcb + 1	; Load HL with address of Standard FCB + 1
+	LD D, 8+3	; Prepare a counter for 8+3 characters for a full filename
+START	LD E, (HL)	; Load content of address in HL into E
+	LD C, conout	; Prepare a Console Character Out BDOS call
+	PUSH HL		; BDOS call clobbers HL, push to stack
+	CALL bdos 	; Go to BDOS for conout call
+	POP HL 		; Restore HL after BDOS call
+	INC HL 		; Next byte
+	DEC D  		; .. until all needed characters..
+	JR NZ, START
+
+	; --- START OF FILE OPEN
+	; To open file for sequential access, the 'cr' field of the FCB needs
+	; to be zeroed
+	LD HL, fcbcr	; Set the HL register pair to the CR field address
+	LD (HL), 0	; Set to zero
+
+	LD DE, sfcb	; Prepare DE with address of FCB
+	LD C, openf	; Set up for Open File BDOS call
+	CALL bdos	; GO!
+
+	CP 255		; Compare A register to check for error
+	JR Z, ERROPF	; If Zero set, A == 255, and we have an error
+	; --- END OF FILE OPEN
+
+	LD DE, okmsg	; Compare did not set Zero flag, so we can
+	LD C, strout	; use String Output to say that the file is opened
+	CALL bdos
+
+	; --- ACTUAL DATA REA
+RREC	LD DE, sfcb	; Load DE with address of FCB
+	LD C, reads	; and perform a sequential file read
+	CALL bdos	; BDOS will look at the FCB and retrieve the appropriate block
+
+	CP 0		; Check for errors on read. If we see anything other than
+	JR NZ, ERRRDD	; a zero, we have something wonky on the read.
+	; --- DMA buffer now contains 128 bytes from file
+
+	; --- Fluff of code to read through file
+	LD D, 128	; Prepare for counting through 128 bytes record...
+	LD HL, sdma	; Using the HL as a pointer to positions on DMA buffer
+PRTBYTE	LD E, (HL)	; Load content of address in HL into E
+
+	; This bit works for text, will be wonky if the file is binary
+	; But, it seems that if a record is not full, it's supposed to get
+	; filled with EOF characters until end...
+	LD A, eof	; Check for EOF character
+	CP E		; If cound, we're at the end of file
+	JR Z, DONE	; .. so jump to done
+
+	LD C, conout	; Prepare a Console Character Out BDOS call
+	PUSH HL		; BDOS call clobbers HL, push to stack
+	CALL bdos 	; Go to BDOS for conout call
+	POP HL 		; Restore HL after BDOS call
+	INC HL 		; Next byte
+	DEC D  		; .. until all needed characters..
+	JR NZ, PRTBYTE
+
+	; If we've gotten here, we have completed one 128 byte set, and
+	; haven't seen any EOF characters yet. So, try to get a new one.
+	JP RREC		; Jump to read next record from file.
+
+
+DONE	LD DE, donemsg	; Do a quick status at the end of completion...
+	LD C, strout
+	CALL bdos
+	JP  0		; Do a jump to BOOT, causing a boot to CCP
+
+ERROPF	LD DE, erropn
+	JP ERROR
+ERRRDD	LD DE, errrd
+	JP ERROR
+
+ERROR	LD C, strout
+	CALL bdos
+	JP  0		; Do a jump to BOOT, causing a boot to CCP
+
+erropn	ASC "\r\n---> ERROR opening file\r\n$"
+errrd	ASC "\r\n---> ERROR reading file\r\n$"
+okmsg	ASC "\r\n---> Opened file\r\n$"
+donemsg	ASC "\r\n---> Completed reading file.\r\n$"
+