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usb-loader: Explain a little more about magic calls

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These calls enter into the MT6260 ROM.  Explain a bit more about where they
come from and what their function prototypes are.

Signed-off-by: Sean Cross <xobs@kosagi.com>
This commit is contained in:
Sean Cross 2015-02-19 18:54:34 +08:00
parent 91d05709fc
commit 8a4f98b5b1
1 changed files with 13 additions and 2 deletions
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15
usb-loader.S
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@ -20,6 +20,15 @@ load_program:
adr r0, size_buffer
mov r1, #4
mvn r2, #0
# This function address was discovered by disassembling the ROM, which
# begins around offset 0xfff00000. When the MTK Flash Tool loads code into
# an unflashed MTK chip, it makes calls to a few well-defined positions that
# contain pointers to read a buffer, write a buffer, and flush the current
# write buffer. The programming interface is the same for both USB and
# serial. However, since the MT6260 series of parts primarily boots
# off of USB, we are only interested in the USB thunks.
# The prototype for this function is:
# void usb_uart_read(void *buffer, int bytes, int timeout)
ldr r3, =0xfff03639
blx r3
@ -62,11 +71,13 @@ uart_puts_count_chars_loop:
uart_puts_print:
mvn r2, #0
// Call usb_uart_write(char *data, int bytes, int timeout)
# Call:
# void usb_uart_write(char *data, int bytes, int timeout)
ldr r3, =0xfff03653
blx r3
// Call usb_uart_flush
# Call:
# void usb_uart_flush(void)
ldr r3, =0xfff04845
blx r3