Avoid long pauses on serial timeout on boot on physical hardware.

[pintos-anon] / src / threads / loader.S

diff --git a/src/threads/loader.S b/src/threads/loader.S
index a5819dd28429080f7e6e5f7b70dd277579d12950..dd87ea1c794bc1759ceca654fc953eaea082d763 100644 (file)
--- a/src/threads/loader.S
+++ b/src/threads/loader.S
@@ -29,11 +29,12 @@
 # Configure serial port so we can report progress without connected VGA.
 # See [IntrList] for details.
        sub %dx, %dx                    # Serial port 0.
-       mov $0x00e3, %ax                # 9600 bps, N-8-1.
+       mov $0xe3, %al                  # 9600 bps, N-8-1.
+                                       # AH is already 0 (Initialize Port).
        int $0x14                       # Destroys AX.
 
        call puts
-       .string "Pintos loader"
+       .string "PiLo"
 
 #### Read the partition table on each system hard disk and scan for a
 #### partition of type 0x20, which is the type that we use for a
@@ -209,8 +210,12 @@ putc:      pusha
 
        mov $0x01, %ah                  # Serial port output service.
        sub %dx, %dx                    # Serial port 0.
-       int $0x14                       # Destroys AH.
+2:     int $0x14                       # Destroys AH.
+       test $0x80, %ah                 # Output timed out?
+       jz 3f
+       movw $0x9090, 2b                # Turn "int $0x14" above into NOPs.
 
+3:
        cmp $'\r', %al
        jne popa_ret
        mov $'\n', %al
@@ -224,8 +229,9 @@ putc:       pusha
 
 read_sector:
        pusha
-       sub %eax, %eax
-       push %eax                       # LBA sector number [32:63]
+       sub %ax, %ax
+       push %ax                        # LBA sector number [48:63]
+       push %ax                        # LBA sector number [32:47]
        push %ebx                       # LBA sector number [0:31]
        push %es                        # Buffer segment
        push %ax                        # Buffer offset (always 0)