[SeaBIOS] [PATCH 6/6] Use timer_check() instead of using floppy_motor_counter in BDA for the timeout check in floppy_wait_irq()

Nikolay Nikolov nickysn at users.sourceforge.net
Sat Feb 3 18:32:55 CET 2018

The problem with using floppy_motor_counter was that, after it reaches 0,
it immediately stops the floppy motors, which is not what is supposed to
happen on real hardware. Instead, after a timeout (like in the end of
every floppy operation, regardless of the result - success, timeout or
error), the floppy motors must be kept spinning for additional 2 seconds
(the FLOPPY_MOTOR_TICKS). So, now the floppy_motor_counter is initialized
to 255 (the max value) in the beginning of the floppy operation (in
floppy_turn_on_motor()). For IRQ timeouts, a different timeout is used,
specified by the new FLOPPY_IRQ_TIMEOUT constant (currently set to 5
seconds - a fairly conservative value, but should work reliably on most

After the floppy operation, floppy_turn_off_motor_delayed() resets the
floppy_motor_counter to 2 seconds (FLOPPY_MOTOR_TICKS).

This is also consistent with what other PC BIOSes do.

Signed-off-by: Nikolay Nikolov <nickysn at users.sourceforge.net>
 src/hw/floppy.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/hw/floppy.c b/src/hw/floppy.c
index acaff3f..6714402 100644
--- a/src/hw/floppy.c
+++ b/src/hw/floppy.c
@@ -34,6 +34,7 @@
 #define FLOPPY_GAPLEN 0x1B
 #define FLOPPY_PIO_TIMEOUT 1000
+#define FLOPPY_IRQ_TIMEOUT 5000
 #define FLOPPY_DOR_MOTOR_D     0x80 // Set to turn drive 3's motor ON
 #define FLOPPY_DOR_MOTOR_C     0x40 // Set to turn drive 2's motor ON
@@ -221,8 +222,9 @@ floppy_wait_irq(void)
     u8 frs = GET_BDA(floppy_recalibration_status);
     SET_BDA(floppy_recalibration_status, frs & ~FRS_IRQ);
+    u32 end = timer_calc(FLOPPY_IRQ_TIMEOUT);
     for (;;) {
-        if (!GET_BDA(floppy_motor_counter)) {
+        if (timer_check(end)) {
             return DISK_RET_ETIMEOUT;
@@ -340,8 +342,8 @@ floppy_enable_controller(void)
 static void
 floppy_turn_on_motor(u8 floppyid)
-    // reset the disk motor timeout value of INT 08
-    SET_BDA(floppy_motor_counter, FLOPPY_MOTOR_TICKS);
+    // set the disk motor timeout value of INT 08 to the highest value
+    SET_BDA(floppy_motor_counter, 255);
     // Turn on motor of selected drive, DMA & int enabled, normal operation
     floppy_dor_write((floppyid ? FLOPPY_DOR_MOTOR_B : FLOPPY_DOR_MOTOR_A) | FLOPPY_DOR_IRQ | FLOPPY_DOR_RESET | floppyid);

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