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

Gedare Bloom gedare at rtems.org
Wed Nov 12 15:54:07 UTC 2014


On Wed, Nov 12, 2014 at 10:07 AM, Jan Dolezal <dolezj21 at fel.cvut.cz> wrote:
> ---
>  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
These new files should probably go under i386/shared/irq  ?

>
> 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>
Why include string.h?

I have more comments below in the .h file. I am not reviewing this .c
file due to time constraints and my lack of confidence in x86
assembly, but I will say if the below macros and struct defines are
useful outside this file, then they should go into a header file
instead. Also, I think we use __volatile__ for declaring ASM blocks.
(We ought to have an RTEMS macro for this, e.g. RTEMS_INLINE_ASM(),
but I don't think we do.)

> +#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__));
> +
RTEMS prefers to use typedef on struct names. Also, the name should be
"namespaced", for example, i386_interrupt_registers. Usually I would
expect to see this kind of structure in
score/cpu/i386/rtems/score/i386.h defined as an interrupt context
structure. I think ARM has an example.

Is __packed__ necessary? We avoid compiler attributes where possible,
and where necessary we should use a macro e.g. RTEMS_PACKED_STRUCT (or
something, if it exists).

> +/**
> + * 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);
> +
avoid abbreviations, use realmode

What does "primary"  mean? Is there a "secondary"? If not, just use
i386_get_realmode_buffer().


> +/**
> + * returns size of real mode buffer
> + *
> + * @return size of buffer
> + */
> +extern uint16_t i386_get_primary_rm_buffer_size(void);
> +
The above two functions can be merged together, where the buffer is
returned and the size gets set as a side-effect, if that is useful.

> +/* 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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