[prefix] Prompt for entering gPXE shell during POST

The ROM prefix now prompts the user to enter the gPXE shell during POST;
this allows for configuring gPXE without needing to attempt to boot from
it.  (It also slows down system boot by three seconds per gPXE ROM, but
hey.)

This is apparently a certain OEM's requirement for option ROMs.

diff --git a/src/arch/i386/prefix/romprefix.S b/src/arch/i386/prefix/romprefix.S
index 882da18b037fb728e674787df114c0c5c76e558f..19e6a9b380f65bebea7668b416a176db4c317f1d 100644 (file)
--- a/src/arch/i386/prefix/romprefix.S
+++ b/src/arch/i386/prefix/romprefix.S
@@ -130,9 +130,12 @@ init:
        pushaw
        pushw   %ds
        pushw   %es
+       pushw   %fs
        cld
        pushw   %cs
        popw    %ds
+       pushw   $0x40
+       popw    %fs
        movw    %di, %bx
        xorw    %di, %di
        /* Print message as early as possible */
@@ -227,11 +230,53 @@ gotpmm:   /* PMM allocation succeeded: copy ROM to PMM block */
        loop    1b
        subb    %bl, checksum
        popal
-no_pmm:
-       /* Print CRLF to terminate messages */
-       movw    $'\n', %ax
-       call    print_character
+no_pmm:        /* Prompt for POST-time shell */
+       movw    $init_message_prompt, %si
+       call    print_message
+       /* Empty the keyboard buffer before waiting for input */
+empty_keyboard_buffer:
+       movb    $0x01, %ah
+       int     $0x16
+       jz      1f
+       xorw    %ax, %ax
+       int     $0x16
+       jmp     empty_keyboard_buffer
+1:     /* Wait for up to 3s for a key press */
+       movw    $(18 * 3), %cx  /* Approx 3s worth of timer ticks */
+wait_for_key:
+       decw    %cx
+       jz      no_key_pressed
+       /* Wait for timer tick to be updated */
+       movl    %fs:(0x6c), %eax
+1:     pushf
+       sti
+       hlt
+       popf
+       cmpl    %fs:(0x6c), %eax
+       je      1b
+       /* Check to see if a key was pressed */
+       movb    $0x01, %ah
+       int     $0x16
+       jz      wait_for_key
+       /* Check to see if key was Ctrl-B */
+       cmpb    $0x02, %al
+       je      1f
+       /* Key was not Ctrl-B: remove from buffer and stop waiting */
+       xorw    %ax, %ax
+       int     $0x16
+       jmp     no_key_pressed
+1:     /* Key was Ctrl-B: leave in keyboard buffer and invoke gPXE.
+        * The keypress will be picked up by the initial shell
+        * prompt, and we will drop into a shell.
+        */
+       pushw   %cs
+       call    exec
+no_key_pressed:
+       /* Print blank lines to terminate messages */
+       movw    $init_message_end, %si
+       call    print_message
        /* Restore registers */
+       popw    %fs
        popw    %es
        popw    %ds
        popaw
@@ -245,19 +290,25 @@ init_message:
        .size   init_message, . - init_message
 init_message_pnp:
        .asciz  " PnP"
-       .size init_message_pnp, . - init_message_pnp
+       .size   init_message_pnp, . - init_message_pnp
 init_message_bbs:
        .asciz  " BBS"
-       .size init_message_bbs, . - init_message_bbs
+       .size   init_message_bbs, . - init_message_bbs
 init_message_pmm:
        .asciz  " PMM"
-       .size init_message_pmm, . - init_message_pmm
+       .size   init_message_pmm, . - init_message_pmm
 init_message_pmm_failed:
        .asciz  "(failed)"
-       .size init_message_pmm_failed, . - init_message_pmm_failed
+       .size   init_message_pmm_failed, . - init_message_pmm_failed
 init_message_int19:
        .asciz  " INT19"
-       .size init_message_int19, . - init_message_int19
+       .size   init_message_int19, . - init_message_int19
+init_message_prompt:
+       .asciz  "\nPress Ctrl-B to configure gPXE..."
+       .size   init_message_prompt, . - init_message_prompt
+init_message_end:
+       .asciz  "\n\n\n"
+       .size   init_message_end, . - init_message_end
 
 /* ROM image location
  *
@@ -361,7 +412,7 @@ exec:       /* Set %ds = %cs */
        .previous
 
 exec_message:
-       .asciz  "gPXE starting boot\n"
+       .asciz  "Entering gPXE\n"
        .size exec_message, . - exec_message
 
 /* UNDI loader