/*
 * mem_alloc_pages / mem_free_block / mem_get_page / mem_info — ESTEX EMM
 * wrappers for explicit 16 KB-page allocation.
 *
 *   ESTEX $3C INFOMEM    → HL=total pages, BC=free pages
 *   ESTEX $3D GETMEM     B=npages       → A=block id,        CF=err
 *   ESTEX $3E FREEMEM    A=block id     →                    CF=err
 *   BIOS  $C4 EMM_GETPAGE A=blk, B=idx  → A=physical page    CF=err
 *
 * Pattern: every RST 10h / RST 8 is bracketed with push/pop IX because
 * ESTEX/BIOS clobber it and the C caller uses it as a frame pointer.
 */

#include <stdint.h>
#include <sprinter_mem.h>

uint8_t mem_alloc_pages(uint8_t n) __naked
{
    (void)n;
    __asm
        ;; SDCC single-uint8 arg → A on entry.
        push  ix
        ld    b, a
        ld    c, #0x3D
        rst   #0x10
        pop   ix
        jr    c, _alloc_fail
        ret
    _alloc_fail:
        call  __errno_set
        xor   a, a                  ; 0 = failure
        ret
    __endasm;
}

void mem_free_block(uint8_t blk_id) __naked
{
    (void)blk_id;
    __asm
        ;; SDCC single-uint8 arg → A on entry.
        push  ix
        ld    c, #0x3E
        rst   #0x10
        pop   ix
        ret
    __endasm;
}

uint8_t mem_get_page(uint8_t blk_id, uint8_t idx) __naked
{
    (void)blk_id; (void)idx;
    __asm
        ;; 2-arg uint8/uint8: blk_id → A, idx → L.
        push  ix
        ld    b, l                  ; BIOS wants idx in B
        ;; A still has blk_id
        ld    c, #0xC4              ; BIOS EMM_GETPAGE
        rst   #0x08
        pop   ix
        ;; A = physical page number.  Return as uint8 → A.
        ret
    __endasm;
}

void mem_info(uint16_t *total, uint16_t *free_pages) __naked
{
    (void)total; (void)free_pages;
    __asm
        ;; HL = total, DE = free_pages on entry.
        ;; ESTEX INFOMEM clobbers everything; stash both pointers on stack.
        push  ix
        push  hl                    ; [SP+0..1] = total ptr
        push  de                    ; [SP+2..3] = free_pages ptr  (wait wrong order)

        ;; Actually after two pushes: SP+0 = free_pages_ptr, SP+2 = total_ptr.
        ;; That's the layout we'll use below.

        ld    c, #0x3C              ; ESTEX INFOMEM → HL=total, BC=free
        rst   #0x10
        ;; HL = total value, BC = free value.

        pop   de                    ; DE = free_pages ptr
        ld    a, c
        ld    (de), a
        inc   de
        ld    a, b
        ld    (de), a

        pop   de                    ; DE = total ptr
        ld    a, l
        ld    (de), a
        inc   de
        ld    a, h
        ld    (de), a

        pop   ix
        ret
    __endasm;
}