From f1aa2a0abda6cdba69864f6cfaa325f018d508cf Mon Sep 17 00:00:00 2001
From: Will Sowerbutts <will@sowerbutts.com>
Date: Fri, 6 Jan 2017 19:02:15 +0000
Subject: [PATCH] Kernel: n8vem-mark4: Change to dynamic bufpool

---
 Kernel/platform-n8vem-mark4/config.h  |  6 +++---
 Kernel/platform-n8vem-mark4/crt0.s    |  1 +
 Kernel/platform-n8vem-mark4/discard.c |  2 ++
 Kernel/platform-n8vem-mark4/main.c    | 14 ++++++++++++++
 Kernel/platform-n8vem-mark4/mark4.s   |  8 ++++++++
 5 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/Kernel/platform-n8vem-mark4/config.h b/Kernel/platform-n8vem-mark4/config.h
index 4017d22f..8ab6bea5 100644
--- a/Kernel/platform-n8vem-mark4/config.h
+++ b/Kernel/platform-n8vem-mark4/config.h
@@ -25,13 +25,15 @@
 #define PROGBASE    0x0000  /* also data base */
 #define PROGLOAD    0x0100  /* also data base */
 #define PROGTOP     0xF800  /* Top of program, base of U_DATA copy */
+#define KERNTOP     0xF000  /* Kernel has lower 60KB */
 #define PROC_SIZE   64      /* Memory needed per process */
 
 /* We need a tidier way to do this from the loader */
 #define CMDLINE	(0x0081)  /* Location of root dev name */
 #define BOOTDEVICENAMES "hd#,,,rd"
 
-#define NBUFS    10       /* Number of block buffers */
+#define CONFIG_DYNAMIC_BUFPOOL /* we expand bufpool to overwrite the _DISCARD segment at boot */
+#define NBUFS    4        /* Number of block buffers, keep in line with space reserved in mark4.s */
 #define NMOUNTS	 4	  /* Number of mounts at a time */
 
 /* Hardware parameters */
@@ -80,5 +82,3 @@
 	/* ASCI0 as the console */
 	#define TTYDEV   (512+1)  /* System console (used by kernel, init) */
 #endif
-
-#define platform_discard()
diff --git a/Kernel/platform-n8vem-mark4/crt0.s b/Kernel/platform-n8vem-mark4/crt0.s
index e77a5473..28c4b1ce 100644
--- a/Kernel/platform-n8vem-mark4/crt0.s
+++ b/Kernel/platform-n8vem-mark4/crt0.s
@@ -17,6 +17,7 @@
         .area _HEAP
         ; note that areas below here may be overwritten by the heap at runtime, so
         ; put initialisation stuff in here
+        .area _BUFFERS     ; _BUFFERS grows to consume all before it (up to KERNTOP)
         .area _INITIALIZER
         .area _GSINIT
         .area _GSFINAL
diff --git a/Kernel/platform-n8vem-mark4/discard.c b/Kernel/platform-n8vem-mark4/discard.c
index 49ab4d34..94aadff1 100644
--- a/Kernel/platform-n8vem-mark4/discard.c
+++ b/Kernel/platform-n8vem-mark4/discard.c
@@ -9,6 +9,8 @@ void init_hardware_c(void)
 {
     ramsize = 512;
     procmem = 512 - 64 - (DEV_RD_RAM_PAGES<<2);
+    /* zero out the initial bufpool */
+    memset(bufpool, 0, (char*)bufpool_end - (char*)bufpool);
 }
 
 void pagemap_init(void)
diff --git a/Kernel/platform-n8vem-mark4/main.c b/Kernel/platform-n8vem-mark4/main.c
index e91bd394..05d4568c 100644
--- a/Kernel/platform-n8vem-mark4/main.c
+++ b/Kernel/platform-n8vem-mark4/main.c
@@ -8,6 +8,20 @@
 uint16_t ramtop = PROGTOP;
 extern unsigned char irqvector;
 
+struct blkbuf *bufpool_end = bufpool + NBUFS; /* minimal for boot -- expanded after we're done with _DISCARD */
+
+void platform_discard(void)
+{
+    while(bufpool_end < (struct blkbuf*)(KERNTOP - sizeof(struct blkbuf))){
+        memset(bufpool_end, 0, sizeof(struct blkbuf));
+#if BF_FREE != 0
+        bufpool_end->bf_busy = BF_FREE; /* redundant when BF_FREE == 0 */
+#endif
+        bufpool_end->bf_dev = NO_DEVICE;
+        bufpool_end++;
+    }
+}
+
 void z180_timer_interrupt(void)
 {
     unsigned char a;
diff --git a/Kernel/platform-n8vem-mark4/mark4.s b/Kernel/platform-n8vem-mark4/mark4.s
index 1b7d0d52..98da09f1 100644
--- a/Kernel/platform-n8vem-mark4/mark4.s
+++ b/Kernel/platform-n8vem-mark4/mark4.s
@@ -10,6 +10,7 @@
         .globl inchar
         .globl outchar
         .globl platform_interrupt_all
+        .globl _bufpool
 
         ; imported symbols
         .globl z180_init_hardware
@@ -21,6 +22,13 @@
         .include "../cpu-z180/z180.def"
         .include "../kernel.def"
 
+; -----------------------------------------------------------------------------
+; Buffers
+; -----------------------------------------------------------------------------
+        .area _BUFFERS
+_bufpool:
+        .ds (BUFSIZE * 4) ; adjust NBUFS in config.h in line with this
+
 ; -----------------------------------------------------------------------------
 ; Initialisation code
 ; -----------------------------------------------------------------------------
-- 
2.34.1