From a804375560c6f10cad779fc914bd10e2b1758764 Mon Sep 17 00:00:00 2001
From: David Given <dg@cowlark.com>
Date: Tue, 11 Jun 2019 20:32:00 +0200
Subject: [PATCH] Miscellaneous byte shaving; you can now choose whether or not
 you want the CCP overwritten or not, and cpm_exit() does the right thing.

---
 plat/cpm/boot.s                     | 44 ++++++++++++++++-------------
 plat/cpm/include/cpm.h              | 11 +++++---
 plat/cpm/libsys/brk.c               | 17 +++++------
 plat/cpm/libsys/cpm_overwrite_ccp.s | 12 ++++++++
 4 files changed, 51 insertions(+), 33 deletions(-)
 create mode 100644 plat/cpm/libsys/cpm_overwrite_ccp.s

diff --git a/plat/cpm/boot.s b/plat/cpm/boot.s
index 64f85fd2a..1330e8309 100644
--- a/plat/cpm/boot.s
+++ b/plat/cpm/boot.s
@@ -22,12 +22,13 @@ begtext:
 	! BDOS and crash CP/M.  We cheat by comparing only high bytes
 	! of each address.
 
-	lxi b, __end
 	lda 0x0007
-	mov c, a		! c = high byte of BDOS address
-	mov a, b		! a = high byte of _end
+	mov c, a        ! c = high byte of BDOS address
+	lda _cpm_ram+1  ! a = high byte of top of BSS, a.k.a. _end
 	cmp c
-	rnc       		! emergency exit if a >= c
+	lxi d, noroom
+	mvi c, 9
+	jnc 0x0005      ! print error and exit if a >= c
 
 	! We have to clear the bss. (argify requires it.)
 	
@@ -59,8 +60,10 @@ begtext:
 
     ! Now the 'heap'.
 
-	lxi h, __end
-	shld _cpm_ram
+	lhld 0x0006              ! BDOS entry point
+	lxi d, -0x806            ! offset to start of CCP
+	dad d                    
+	shld _cpm_ramtop
 
 	! C-ify the command line at 0x0080.
 
@@ -127,31 +130,29 @@ end_of_argify:
 	lhld argc                ! slightly evil
 	mvi h, 0
 	push h
-	push h                   ! return address is 0
-	jmp __m_a_i_n
-
-.define _cpm_fastexit
-_cpm_fastexit:
-saved_sp = _cpm_fastexit + 1
+	call __m_a_i_n
+.define _cpm_exit, EXIT, __exit
+_cpm_exit:
+EXIT:
+__exit:
+	stc                      ! set carry bit
+	jnc _cpm_warmboot        ! warm boot if not set
+saved_sp = . + 1
 	lxi sp, 0                ! patched on startup
 	ret
 
 ! Emergency exit routine.
 
-.define EXIT, __exit, _cpm_exit
-EXIT = 0
-__exit = 0
-_cpm_exit = 0
+.define _cpm_warmboot
+_cpm_warmboot = 0
 	
 ! Special CP/M stuff.
 
 .define _cpm_fcb
 _cpm_fcb = 0x005c
 
-.define _cpm_ram
-.comm _cpm_ram, 2
 .define _cpm_ramtop
-_cpm_ramtop = 0x0001
+.comm _cpm_ramtop, 2
 
 .define _cpm_default_dma
 _cpm_default_dma = 0x0080
@@ -197,5 +198,10 @@ block1: .space 4        ! used by 32 bits divide and
 block2: .space 4        ! multiply routines
 block3: .space 4        ! must be contiguous (.comm doesn't guarantee this)
 
+.sect .data
+.define _cpm_ram
+_cpm_ram: .data2 __end
+
 .sect .rom
 progname: .asciz 'ACKCPM'
+noroom: .ascii 'No room$'
diff --git a/plat/cpm/include/cpm.h b/plat/cpm/include/cpm.h
index 9a354eb03..81dfa5dab 100644
--- a/plat/cpm/include/cpm.h
+++ b/plat/cpm/include/cpm.h
@@ -67,11 +67,14 @@ extern uint8_t* cpm_ramtop;
 extern uint8_t cpm_cmdlinelen;
 extern char cpm_cmdline[0x7f];
 
-/* Special: longjmps out of the program. Don't use if you've overwritten the
- * CCP. */
-extern void cpm_fastexit(void);
+/* Special: if the CCP hasn't been overwritten, returns to it; otherwise does
+ * a warmboot. */
+extern void cpm_exit(void);
 
-/*  0 */ extern void cpm_exit(void);
+/* Extends cpm_ramtop over the CCP, for a little extra space. */
+extern void cpm_overwrite_ccp(void);
+
+/*  0 */ extern void cpm_warmboot(void);
 /*  1 */ extern uint8_t cpm_conin(void);
 /*  2 */ extern void cpm_conout(uint8_t b);
 /*  3 */ extern uint8_t cpm_auxin(void);
diff --git a/plat/cpm/libsys/brk.c b/plat/cpm/libsys/brk.c
index e9f13c1e6..5debaa5ff 100644
--- a/plat/cpm/libsys/brk.c
+++ b/plat/cpm/libsys/brk.c
@@ -1,32 +1,29 @@
 #include <cpm.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <errno.h>
 #include <unistd.h>
 
 #define	OUT_OF_MEMORY (void*)(-1)	/* sbrk returns this on failure */
-#define STACK_BUFFER 128 /* number of bytes to leave for stack */
 
-extern char _end[1];
+extern uint8_t _end[1];
 
 int brk(void* newend)
 {
-	/* We determine the amount of free memory by looking at the address of the
-	 * BDOS vector at 0x0006. */
-	char* memtop = (char*) ((*(unsigned char*)0x0007)<<8);
-	char* p = newend;
+	uint8_t* p = newend;
 	
-	if ((p >= memtop) ||
+	if ((p >= cpm_ramtop) ||
 	    (p < _end))	
 		return -1;
 		
-	cpm_ram = p;
+	cpm_ram = (uint8_t*)p;
 	return 0;
 }
 
 void* sbrk(int increment)
 {
-	char* old;
-	char* new;
+	uint8_t* old;
+	uint8_t* new;
 	
 	if (increment == 0)
 		return cpm_ram;
diff --git a/plat/cpm/libsys/cpm_overwrite_ccp.s b/plat/cpm/libsys/cpm_overwrite_ccp.s
new file mode 100644
index 000000000..78083b770
--- /dev/null
+++ b/plat/cpm/libsys/cpm_overwrite_ccp.s
@@ -0,0 +1,12 @@
+#
+#include "asm.h"
+
+.define _cpm_overwrite_ccp
+_cpm_overwrite_ccp:
+	mvi a, 0xaf              ! 0xaf = xor a = clear carry bit
+	sta _cpm_exit
+    lhld _cpm_ramtop
+    lxi d, 0x800
+    dad d
+    shld _cpm_ramtop
+	ret