[PATCH 4/6] i386/shared/int16: real mode interrupt interface

Jan Dolezal dolezj21 at fel.cvut.cz
Wed Nov 12 15:07:54 UTC 2014


---
 c/src/lib/libbsp/i386/pc386/Makefile.am    |   2 +
 c/src/lib/libbsp/i386/pc386/preinstall.am  |   4 +
 c/src/lib/libbsp/i386/shared/int16/int16.c | 397 +++++++++++++++++++++++++++++
 c/src/lib/libbsp/i386/shared/int16/int16.h |  93 +++++++
 4 files changed, 496 insertions(+)
 create mode 100644 c/src/lib/libbsp/i386/shared/int16/int16.c
 create mode 100644 c/src/lib/libbsp/i386/shared/int16/int16.h

diff --git a/c/src/lib/libbsp/i386/pc386/Makefile.am b/c/src/lib/libbsp/i386/pc386/Makefile.am
index 9c901df..6042b5b 100644
--- a/c/src/lib/libbsp/i386/pc386/Makefile.am
+++ b/c/src/lib/libbsp/i386/pc386/Makefile.am
@@ -29,6 +29,7 @@ SUBDIRS = . tools
 include_bsp_HEADERS  = ../../i386/shared/irq/irq.h
 include_bsp_HEADERS += ../../i386/shared/irq/irq_asm.h
 include_bsp_HEADERS += ../../i386/shared/comm/tty_drv.h
+include_bsp_HEADERS += ../../i386/shared/int16/int16.h
 include_bsp_HEADERS += ../../shared/include/irq-generic.h
 include_bsp_HEADERS += ../../shared/include/irq-info.h
 include_bsp_HEADERS += console/rtd316.h
@@ -94,6 +95,7 @@ libbsp_a_SOURCES += console/kbd_parser.c
 libbsp_a_SOURCES += console/serial_mouse_config.c
 libbsp_a_SOURCES += ../../i386/shared/comm/uart.c
 libbsp_a_SOURCES += ../../i386/shared/comm/tty_drv.c
+libbsp_a_SOURCES += ../../i386/shared/int16/int16.c
 libbsp_a_SOURCES += ../../shared/console.c
 libbsp_a_SOURCES += console/console_select.c
 libbsp_a_SOURCES += ../../shared/console_read.c
diff --git a/c/src/lib/libbsp/i386/pc386/preinstall.am b/c/src/lib/libbsp/i386/pc386/preinstall.am
index aff01dc..1ff9fb8 100644
--- a/c/src/lib/libbsp/i386/pc386/preinstall.am
+++ b/c/src/lib/libbsp/i386/pc386/preinstall.am
@@ -69,6 +69,10 @@ $(PROJECT_INCLUDE)/bsp/tty_drv.h: ../../i386/shared/comm/tty_drv.h $(PROJECT_INC
 	$(INSTALL_DATA) $< $(PROJECT_INCLUDE)/bsp/tty_drv.h
 PREINSTALL_FILES += $(PROJECT_INCLUDE)/bsp/tty_drv.h
 
+$(PROJECT_INCLUDE)/bsp/int16.h: ../../i386/shared/int16/int16.h $(PROJECT_INCLUDE)/bsp/$(dirstamp)
+	$(INSTALL_DATA) $< $(PROJECT_INCLUDE)/bsp/int16.h
+PREINSTALL_FILES += $(PROJECT_INCLUDE)/bsp/int16.h
+
 $(PROJECT_INCLUDE)/bsp/irq-generic.h: ../../shared/include/irq-generic.h $(PROJECT_INCLUDE)/bsp/$(dirstamp)
 	$(INSTALL_DATA) $< $(PROJECT_INCLUDE)/bsp/irq-generic.h
 PREINSTALL_FILES += $(PROJECT_INCLUDE)/bsp/irq-generic.h
diff --git a/c/src/lib/libbsp/i386/shared/int16/int16.c b/c/src/lib/libbsp/i386/shared/int16/int16.c
new file mode 100644
index 0000000..380188f
--- /dev/null
+++ b/c/src/lib/libbsp/i386/shared/int16/int16.c
@@ -0,0 +1,397 @@
+/*
+ *  Realmode interrupt call implementation.
+ *
+ *
+ *  Copyright (c) 2014 - CTU in Prague
+ *                       Jan Doležal ( dolezj21 at fel.cvut.cz )
+ *
+ *  The license and distribution terms for this file may be
+ *  found in the file LICENSE in this distribution or at
+ *  http://www.rtems.org/license/LICENSE.
+ *
+ */
+
+#include <bsp/int16.h>
+#include <string.h>
+#include <rtems/score/cpu.h>
+
+#define IR_EAX_OFF      "0x00"
+#define IR_EBX_OFF      "0x04"
+#define IR_ECX_OFF      "0x08"
+#define IR_EDX_OFF      "0x0C"
+#define IR_ESI_OFF      "0x10"
+#define IR_EDI_OFF      "0x14"
+#define IR_DS_OFF       "0x18"
+#define IR_ES_OFF       "0x1A"
+#define IR_FS_OFF       "0x1C"
+#define IR_GS_OFF       "0x1E"
+
+#define BKP_ESP_OFF     "0x20"
+#define BKP_SS_OFF      "0x24"
+#define BKP_DS_OFF      "0x26"
+#define RM_ENTRY        "0x28"
+#define PM_ENTRY        "0x2C"
+
+/* parameters, results, backup values accessible in real mode */
+struct rm_int_regs_bkp_param {
+    struct interrupt_registers inoutregs;
+    uint32_t pm_esp_bkp;
+    uint16_t pm_ss_bkp;
+    uint16_t ds_bkp;
+    uint16_t rm_entry;
+    uint16_t rm_code_segment;
+    uint32_t pm_entry;
+    uint16_t pm_code_selector;
+    /* if modifying update offset definitions as well */
+}__attribute__((__packed__));
+
+#define BKP_IDTR_LIM    "0x00"
+#define BKP_IDTR_BASE   "0x02"
+#define BKP_ES_OFF      "0x06"
+#define BKP_FS_OFF      "0x08"
+#define BKP_GS_OFF      "0x0A"
+#define RML_ENTRY       "0x0C"
+#define RML_D_SEL       "0x12"
+#define RM_SS           "0x14"
+#define RM_SP           "0x16"
+#define RM_DS           "0x18"
+/* backup values, pointers/parameters accessible in protected mode */
+struct pm_bkp_and_param {
+    uint16_t idtr_lim_bkp;
+    uint32_t idtr_base_bkp;
+    uint16_t es_bkp;
+    uint16_t fs_bkp;
+    uint16_t gs_bkp;
+    uint32_t rml_entry;
+    uint16_t rml_code_selector;
+    uint16_t rml_data_selector;
+    uint16_t rm_stack_segment;
+    uint16_t rm_stack_pointer;
+    uint16_t rm_data_segment;
+}__attribute__((__packed__));
+
+/* addresses where we are going to put Interrupt buffer,
+ * parameter/returned/preserved values, stack and copy code
+ * for calling BIOS interrupt real mode interface
+ * The value is chosen arbitrarily in the first 640kB
+ * to be accessible for real mode. It should be out of range
+ * used by RTEMS because its base address is above 1MB.
+ * It has to be above first 4kB (or better 64kB) which could
+ * be used by BIOS.
+ */
+#define REAL_MODE_SPOT   0x12000
+/* REAL_MODE_SPOT value is also top of real mode stack */
+
+/* buffers positions and lengths */
+#define DEFAULT_BUFFER_SIZE             512
+static void *first_rm_buffer_spot = (void *)REAL_MODE_SPOT;
+static uint16_t first_rm_buffer_size = DEFAULT_BUFFER_SIZE;
+
+/* real mode stack */
+#define STACK_SIZE                      8192
+#define INT_STACK_TOP                   REAL_MODE_SPOT
+
+/******************************
+ * STACK            *         *
+ ****************************** REAL_MODE_SPOT
+ * INT_BUF          * 512 B   *
+ ******************************
+ * INT_REGs         *  50 B   *
+ ******************************
+ * INT_FNC          *~149 B   *
+ ******************************/
+
+#define __DP_TYPE       uint8_t
+#define __DP_YES        ((__DP_TYPE)1)
+#define __DP_NO         ((__DP_TYPE)-1)
+#define __DP_FAIL       ((__DP_TYPE)0)
+static __DP_TYPE descsPrepared = __DP_NO;
+
+/* rml - real mode alike */
+#define rml_limit 0xFFFF
+static uint16_t rml_code_dsc_index = 0;
+static uint16_t rml_data_dsc_index = 0;
+
+/*
+ * Prepares real-mode like descriptors to be used for switching
+ * to real mode.
+ *
+ * @return __DP_YES descriptors are prepared
+ * @return __DP_FAIL descriptors allocation failed (GDT too small)
+ */
+static __DP_TYPE prepareRMDescriptors (void *base32) {
+    static void *prevBase = (void *)-1;
+    /* check if descriptors were prepared already */
+    if (descsPrepared == __DP_YES && prevBase == base32)
+        return descsPrepared;
+
+    if (descsPrepared == __DP_FAIL)
+        return descsPrepared;
+
+    /* create 'real mode like' segment descriptors, for switching to real mode */
+    rml_code_dsc_index = i386_next_empty_gdt_entry();
+    if (rml_code_dsc_index == 0)
+    {
+        /* not enough space in GDT */
+        descsPrepared = __DP_FAIL;
+        return descsPrepared;
+    }
+
+    segment_descriptors flags_desc;
+    memset(&flags_desc, 0, sizeof(flags_desc));
+    flags_desc.type                = 0xE;      /* bits 4  */
+    flags_desc.descriptor_type     = 0x1;      /* bits 1  */
+    flags_desc.privilege           = 0x0;      /* bits 2  */
+    flags_desc.present             = 0x1;      /* bits 1  */
+    flags_desc.available           = 0x0;      /* bits 1  */
+    flags_desc.fixed_value_bits    = 0x0;      /* bits 1  */
+    flags_desc.operation_size      = 0x0;      /* bits 1  */
+    flags_desc.granularity         = 0x0;      /* bits 1  */
+    i386_fill_segment_desc_base((unsigned)base32, &flags_desc);
+    i386_fill_segment_desc_limit(rml_limit, &flags_desc);
+    if (i386_raw_gdt_entry(rml_code_dsc_index, &flags_desc) == 0)
+    {
+        /* selector to GDT out of range */
+        descsPrepared = __DP_FAIL;
+        return descsPrepared;
+    }
+
+    rml_data_dsc_index = i386_next_empty_gdt_entry();
+    if (rml_data_dsc_index == 0)
+    {
+        /* not enough space in GDT for both descriptors */
+        descsPrepared = __DP_FAIL;
+        return descsPrepared;
+    }
+
+    flags_desc.type                = 0x2;      /* bits 4  */
+    if (i386_raw_gdt_entry(rml_data_dsc_index, &flags_desc) == 0)
+    {
+        /* selector to GDT out of range */
+        descsPrepared = __DP_FAIL;
+        return descsPrepared;
+    }
+    prevBase = base32;
+    descsPrepared = __DP_YES;
+    return descsPrepared;
+}
+
+inline void *i386_get_primary_rm_buffer() {
+    return first_rm_buffer_spot;
+}
+
+inline uint16_t i386_get_primary_rm_buffer_size() {
+    return first_rm_buffer_size;
+}
+
+int i386_real_interrupt_call(uint8_t interruptNumber, struct interrupt_registers *ir){
+    uint32_t pagingon;
+    struct rm_int_regs_bkp_param *int_passed_regs_spot;
+    /* place where the code switching to realmode and executing
+       interrupt is coppied */
+    void *rm_swtch_code_dst;
+    void *rm_stack_top;
+
+    size_t cpLength;
+    void *cpBeg;
+
+    /* values that can be passed from protected mode are stored in this struct
+       and they are passed later to the inline assembler executing interrupt */
+    volatile struct pm_bkp_and_param pm_bkp, *pm_bkp_addr;
+    unsigned short unused_offset;
+
+    __asm__ volatile(   "\t"
+        "movl    %%cr0, %%eax\n\t"
+        "andl    %1, %%eax\n"
+        : "=a"(pagingon)
+        : "i"(CR0_PAGING)
+    );
+    if (pagingon)
+        return 0;
+
+    /* located under 1MB for real mode to be able to get/set values */
+    int_passed_regs_spot = (struct rm_int_regs_bkp_param *)
+                                (first_rm_buffer_spot+first_rm_buffer_size);
+    /* position for real mode code reallocation to the first 1MB of RAM */
+    rm_swtch_code_dst = (void *)((uint32_t)int_passed_regs_spot+sizeof(*int_passed_regs_spot));
+    rm_stack_top = (void *)INT_STACK_TOP;
+
+    if (prepareRMDescriptors(int_passed_regs_spot) != __DP_YES)
+        return 0;
+
+    pm_bkp_addr = &pm_bkp;
+    i386_Physical_to_real_mode_ptr(
+        rm_stack_top - STACK_SIZE,
+        (unsigned short *)&pm_bkp.rm_stack_segment,
+        (unsigned short *)&pm_bkp.rm_stack_pointer
+    );
+    pm_bkp.rm_stack_pointer += STACK_SIZE;
+    pm_bkp.rml_code_selector = (rml_code_dsc_index<<3);
+    pm_bkp.rml_entry = ((uint32_t)rm_swtch_code_dst-(uint32_t)int_passed_regs_spot);
+    pm_bkp.rml_data_selector = (rml_data_dsc_index<<3);
+    i386_Physical_to_real_mode_ptr(
+        int_passed_regs_spot,
+        (unsigned short *)&pm_bkp.rm_data_segment,
+        &unused_offset
+    );
+
+    int_passed_regs_spot->inoutregs = *ir;
+    /* offset from the beginning of coppied code */
+    uint16_t rm_entry_offset;
+    __asm__ volatile(
+        "movw   $(rment-cp_beg), %0\n\t"
+        : "=r"(rm_entry_offset)
+    );
+    i386_Physical_to_real_mode_ptr(
+        rm_swtch_code_dst+rm_entry_offset,
+        (unsigned short *)&int_passed_regs_spot->rm_code_segment,
+        (unsigned short *)&int_passed_regs_spot->rm_entry
+    );
+    __asm__ volatile(
+        "movl   $(cp_end), %0\n\t"
+        "movw   %%cs, %1\n\t"
+        : "=mr"(int_passed_regs_spot->pm_entry), "=mr"(int_passed_regs_spot->pm_code_selector)
+    );
+    /* copy code for switch to real mode and executing interrupt to first MB of RAM */
+    __asm__ volatile(   "\t"
+        "mov    $cp_end-cp_beg, %0\n\t"
+        "mov    $cp_beg, %1\n\t"
+        : "=rm"(cpLength), "=rm"(cpBeg)
+    );
+    memcpy(rm_swtch_code_dst, cpBeg, cpLength);
+    /* write interrupt number to be executed */
+    uint16_t interrupt_number_off;
+    uint8_t *interrupt_number_ptr;
+    __asm__ volatile(   "\t"
+        "movw   $intnum-cp_beg, %0\n\t"
+        : "=rm"(interrupt_number_off)
+    );
+    interrupt_number_ptr = (uint8_t *) (rm_swtch_code_dst+interrupt_number_off);
+    *interrupt_number_ptr = interruptNumber;
+    /* execute code that jumps to coppied function, which switches to real mode,
+       loads registers with values passed to interrupt and executes interrupt */
+    __asm__ volatile(   "\t"
+        /* backup stack */
+        "movl    %[regs_spot], %%ebx\n\t"
+        "movl    %%esp, "BKP_ESP_OFF"(%%ebx)\n\t"
+        "movw    %%ss,  "BKP_SS_OFF"(%%ebx)\n\t"
+        /* backup data selector */
+        "movw    %%ds,  "BKP_DS_OFF"(%%ebx)\n\t"
+        /* backup other selectors */
+        "movl    %[pm_bkp], %%esi\n\t"
+        "movw    %%es, "BKP_ES_OFF"(%%esi)\n\t"
+        "movw    %%fs, "BKP_FS_OFF"(%%esi)\n\t"
+        "movw    %%gs, "BKP_GS_OFF"(%%esi)\n\t"
+        /* hopefully loader does not damage interrupt table on the beginning of memory; that means length: 0x3FF, base: 0x0 */
+        /* preserve idtr */
+        "movl    %%esi, %%eax\n\t"
+        "addl    $"BKP_IDTR_LIM", %%eax\n\t"
+        "cli\n\t"
+        "sidt    (%%eax)\n\t"
+        "movl    $rmidt, %%eax\n\t"
+        "lidt    (%%eax)\n\t"
+        /* prepare 'real mode like' data selector */
+        "movw    "RML_D_SEL"(%%esi), %%ax\n\t"
+        /* prepare real mode data segment value */
+        "xorl    %%edx,%%edx\n\t"
+        "movw    "RM_DS"(%%esi), %%dx\n\t"
+        /* prepare real mode stack values */
+        "movw    "RM_SS"(%%esi), %%cx\n\t"
+        "movzwl  "RM_SP"(%%esi), %%esp\n\t"
+        /* jump to copied function and */
+        /* load 'real mode like' code selector */
+        "ljmp   *"RML_ENTRY"(%%esi)\n"
+"rmidt:"/* limit and base for realmode interrupt descriptor table */
+        ".word 0x3FF\n\t"
+        ".long 0\n\t"
+        /* load 'real mode like' data selectors */
+"cp_beg: .code16\n\t"
+        "movw    %%ax, %%ss\n\t"
+        "movw    %%ax, %%ds\n\t"
+        "movw    %%ax, %%es\n\t"
+        "movw    %%ax, %%fs\n\t"
+        "movw    %%ax, %%gs\n\t"
+        /* disable protected mode */
+        "movl    %%cr0, %%eax\n\t"
+        "and     %[cr0_prot_dis], %%ax\n\t"
+        "movl    %%eax, %%cr0\n\t"
+        /* base for data selector of 16-bit protected mode is at beginning of passed regs */
+        /* flush prefetch queue by far jumping */
+        "ljmp    *"RM_ENTRY"\n\t"
+"rment: "
+        /* establish rm stack - esp was already set in 32-bit protected mode*/
+        "movw    %%cx, %%ss\n\t"
+        /* set data segment (value prepared in 32-bit prot mode) */
+        "movw    %%dx, %%ds\n\t"
+        /* count real mode pointer so we don't need to overuse address prefix (by using 32bit address) */
+        "shll    $4,%%edx\n\t"
+        "subl    %%edx,%%ebx\n\t"
+        /* prepare values to be used after interrupt call */
+        "pushw   %%bx\n\t"
+        "pushw   %%ds\n\t"
+        /* fill registers with parameters */
+        "movw    " IR_DS_OFF"(%%bx), %%ax\n\t"
+        "pushw   %%ax\n\t"
+        "movl    "IR_EAX_OFF"(%%bx), %%eax\n\t"
+        "movl    "IR_ECX_OFF"(%%bx), %%ecx\n\t"
+        "movl    "IR_EDX_OFF"(%%bx), %%edx\n\t"
+        "movl    "IR_EDI_OFF"(%%bx), %%edi\n\t"
+        "movl    "IR_ESI_OFF"(%%bx), %%esi\n\t"
+        "movw    " IR_ES_OFF"(%%bx), %%es\n\t"
+        "movw    " IR_FS_OFF"(%%bx), %%fs\n\t"
+        "movw    " IR_GS_OFF"(%%bx), %%gs\n\t"
+        /* prepare ebx register */
+        "movl    "IR_EBX_OFF"(%%bx), %%ebx\n\t"
+        /* prepare ds */
+        "popw    %%ds\n\t"
+        /* interrupt instruction */
+        ".byte   0xCD\n\t"
+"intnum: .byte   0x0\n\t"
+        /* fill return structure */
+        "pushw   %%ds\n\t"
+        "pushl   %%ebx\n\t"
+        "movw    0x6(%%esp), %%ds\n\t"
+        "movw    0x8(%%esp),%%bx\n\t" /* regs_spot */
+        "movl    %%eax,"IR_EAX_OFF"(%%bx)\n\t"
+        "popl    %%eax\n\t"
+        "movl    %%eax,"IR_EBX_OFF"(%%bx)\n\t"
+        "movl    %%ecx,"IR_ECX_OFF"(%%bx)\n\t"
+        "movl    %%edx,"IR_EDX_OFF"(%%bx)\n\t"
+        "movl    %%esi,"IR_ESI_OFF"(%%bx)\n\t"
+        "movl    %%edi,"IR_EDI_OFF"(%%bx)\n\t"
+        "popw    %%ax\n\t"
+        "movw    %%ax, " IR_DS_OFF"(%%bx)\n\t"
+        "movw    %%es, " IR_ES_OFF"(%%bx)\n\t"
+        "movw    %%fs, " IR_FS_OFF"(%%bx)\n\t"
+        "movw    %%gs, " IR_GS_OFF"(%%bx)\n\t"
+        /* prepare protected mode data segment */
+        "movw    "BKP_DS_OFF"(%%bx), %%ax\n\t"
+        /* restore protected mode stack values */
+        "movl    "BKP_ESP_OFF"(%%bx),%%esp\n\t"
+        "movw    "BKP_SS_OFF"(%%bx), %%dx\n\t"
+        /* return to protected mode */
+        "movl    %%cr0, %%ecx     \n\t"
+        "or      %[cr0_prot_ena], %%cx\n\t"
+        "movl    %%ecx, %%cr0     \n\t"
+        "ljmpl   *"PM_ENTRY"(%%bx)\n\t"
+        ".code32\n"
+        /* reload segmentation registers */
+"cp_end:"
+        "movw    %%ax, %%ds\n\t"
+        /* restore stack segment in protected mode context */
+        "movw    %%dx, %%ss\n\t"
+        "movl    %[pm_bkp], %%esi\n\t"
+        "movw    "BKP_ES_OFF"(%%esi), %%es\n\t"
+        "movw    "BKP_FS_OFF"(%%esi), %%fs\n\t"
+        "movw    "BKP_GS_OFF"(%%esi), %%gs\n\t"
+        /* restore IDTR */
+        "addl    $"BKP_IDTR_LIM", %%esi\n\t"
+        "lidt    (%%esi)\n\t"
+        :
+        : [regs_spot]"m"(int_passed_regs_spot), [pm_bkp]"m"(pm_bkp_addr), [cr0_prot_ena]"i"(CR0_PROTECTION_ENABLE), [cr0_prot_dis]"i"(~CR0_PROTECTION_ENABLE)
+        : "memory", "ebx", "ecx", "edx", "esi", "edi"
+    );
+    *ir = int_passed_regs_spot->inoutregs;
+    return 1;
+}
+
diff --git a/c/src/lib/libbsp/i386/shared/int16/int16.h b/c/src/lib/libbsp/i386/shared/int16/int16.h
new file mode 100644
index 0000000..96025ef
--- /dev/null
+++ b/c/src/lib/libbsp/i386/shared/int16/int16.h
@@ -0,0 +1,93 @@
+/**
+ * @file int16.h
+ *
+ * @ingroup i386_shared
+ *
+ * @brief Definitioins supporting real mode interrupt calls.
+ */
+
+/*
+ *  Interface allows calling given interrupt number with content of the
+ *  registers defined. For passing or receiving higher amounts of the data
+ *  there is a buffer accessible from real mode available. Real mode pointer
+ *  to this buffer is passed to the interrupt in the registers.
+ *
+ * Copyright (C) 2014  Jan Doležal (dolezj21 at fel.cvut.cz)
+ *                     CTU in Prague.
+ *
+ *  The license and distribution terms for this file may be
+ *  found in the file LICENSE in this distribution or at
+ *  http://www.rtems.org/license/LICENSE.
+ */
+
+#ifndef _INT16_H
+#define _INT16_H
+
+#include <libcpu/cpu.h>
+#include <stdint.h>
+
+#ifndef ASM /* ASM */
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+/* --- BIOS service interrupt number --- */
+/* number of interrupt servicing video functions */
+#define INTERRUPT_NO_VIDEO_SERVICES 0x10
+
+struct interrupt_registers { /* used for passing parameters, fetching results and preserving values */
+    uint32_t reg_eax;
+    uint32_t reg_ebx;
+    uint32_t reg_ecx;
+    uint32_t reg_edx;
+    uint32_t reg_esi;
+    uint32_t reg_edi;
+    uint16_t reg_ds;
+    uint16_t reg_es;
+    uint16_t reg_fs;
+    uint16_t reg_gs;
+}__attribute__((__packed__));
+
+/**
+ * provides position to real mode buffer, which is buffer
+ * accessible from real mode context - it is located below
+ * address ~0x100000 in order for it to be accessible
+ * This buffer is meant to be pointed to by segReg:GenPurpReg
+ * and through this get bigger portion of information to/from
+ * interrupt service routine.
+ *
+ * @return pointer to buffer
+ */
+extern void *i386_get_primary_rm_buffer(void);
+
+/**
+ * returns size of real mode buffer
+ *
+ * @return size of buffer
+ */
+extern uint16_t i386_get_primary_rm_buffer_size(void);
+
+/* if there is ever need to have more buffers or setting size of the buffer,
+ * feel free to modify the code */
+
+/**
+ * This function allows calling interrupts in real mode and to set processor
+ * registers as desired before interrupt call is made and to retrieve the
+ * registers content after call was made.
+ *
+ * @param interruptNumber interrupt number to be called
+ * @param ir pointer to structure containing registers to be passed to interrupt
+ *        and to retrieve register content after call was made.
+ * @return  0 call failed (GDT too small or pagin is on)
+ *          1 call successful
+ */
+extern int i386_real_interrupt_call(uint8_t interruptNumber, struct interrupt_registers *ir);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* ASM */
+
+#endif /* _INT16_H */
-- 
1.9.1




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