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mem: don't count reserved memory as used upper memory #134

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Merged
stsp merged 1 commit into from
Oct 3, 2026
Merged

mem: don't count reserved memory as used upper memory #134

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35 changes: 21 additions & 14 deletions src/mem.c
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Original file line number Diff line number Diff line change
Expand Up @@ -53,17 +53,15 @@
#define CONV_MAX_KB (UMB_START_SEG / PARAS_PER_KB)

/*
* Above conventional memory, FreeDOS MEM splits the first megabyte the
* way MS-DOS MEM did: 0xA000-0xDFFF is "Upper", and 0xE000-0xFFFF is
* "Reserved" - the BIOS and option ROM area, reported as entirely in
* use. Both are fixed-size regions, not sums of the blocks found in
* them, and free UMBs count towards upper memory wherever they sit.
* Report them the same way, so our numbers can be compared with
* MEM.EXE's directly.
* Above conventional memory, FreeDOS MEM splits what it finds in two:
* the blocks of the upper memory chain are "Upper", and everything else
* below 1 MB is "Reserved" - video memory, option ROMs and the BIOS -
* reported as entirely in use. So upper memory is the sum of the blocks
* themselves, wherever they sit, and the area the chain does not reach
* is reserved rather than used. Report them the same way, so our
* numbers can be compared with MEM.EXE's directly.
*/
#define RESERVED_START_SEG 0xE000
#define UMB_TOTAL_KB ((RESERVED_START_SEG - UMB_START_SEG) / PARAS_PER_KB)
#define RESERVED_TOTAL_KB ((0x10000 - RESERVED_START_SEG) / PARAS_PER_KB)
#define UPPER_AREA_KB ((0x10000 - UMB_START_SEG) / PARAS_PER_KB)

/* Rounds to nearest, as FreeDOS MEM does. */
static uint32_t paras_to_kb(uint32_t paras)
Expand Down Expand Up @@ -572,6 +570,7 @@ void perform_mem(const char *arg)
uint32_t conv_free_paras = 0;
uint32_t conv_largest_paras = 0;

uint32_t umb_total_paras = 0;
uint32_t umb_free_paras = 0;
uint32_t umb_largest_paras = 0;

Expand Down Expand Up @@ -662,7 +661,12 @@ void perform_mem(const char *arg)

/* the MCB header itself belongs to the region it sits in */
if (!is_umb)
{
conv_total_paras += conv_paras + 1;
umb_total_paras += umb_paras;
}
else
umb_total_paras += umb_paras + 1;

if (mcb.owner_psp == 0)
{
Expand Down Expand Up @@ -789,10 +793,13 @@ void perform_mem(const char *arg)
uint32_t conv_free_kb = paras_to_kb(conv_free_paras);
uint32_t conv_used_kb = (conv_total_kb > conv_free_kb) ?
(conv_total_kb - conv_free_kb) : 0;
uint32_t umb_total_kb = UMB_TOTAL_KB;
uint32_t umb_total_kb = paras_to_kb(umb_total_paras);
uint32_t umb_free_kb = paras_to_kb(umb_free_paras);
uint32_t umb_used_kb = (umb_total_kb > umb_free_kb) ?
(umb_total_kb - umb_free_kb) : 0;
/* what the chain never reached is reserved, not used upper memory */
uint32_t reserved_total_kb = (UPPER_AREA_KB > umb_total_kb) ?
(UPPER_AREA_KB - umb_total_kb) : 0;

if (opt_classify)
{
Expand Down Expand Up @@ -924,7 +931,7 @@ void perform_mem(const char *arg)
"Upper", str_tot, str_used, str_free);
print_line(line_buf);

format_kb(RESERVED_TOTAL_KB, str_tot, sizeof(str_tot));
format_kb(reserved_total_kb, str_tot, sizeof(str_tot));
format_kb(0, str_free, sizeof(str_free));
snprintf(line_buf, sizeof(line_buf), "%-16s %8s %8s %8s",
"Reserved", str_tot, str_tot, str_free);
Expand All @@ -942,9 +949,9 @@ void perform_mem(const char *arg)

print_line("---------------- -------- -------- --------");

format_kb(conv_total_kb + umb_total_kb + RESERVED_TOTAL_KB + xms_total_kb,
format_kb(conv_total_kb + umb_total_kb + reserved_total_kb + xms_total_kb,
str_tot, sizeof(str_tot));
format_kb(conv_used_kb + umb_used_kb + RESERVED_TOTAL_KB + xms_used_kb,
format_kb(conv_used_kb + umb_used_kb + reserved_total_kb + xms_used_kb,
str_used, sizeof(str_used));
format_kb(conv_free_kb + umb_free_kb + xms_free_kb, str_free, sizeof(str_free));
snprintf(line_buf, sizeof(line_buf), "%-16s %8s %8s %8s",
Expand Down