rolo: simplify parsing scramble header in load_firmware()

The standard load_firmware() function is used on targets which
use the "scramble -add" method for generating Rockbox binaries.

While it tries to be a bit more generic and allows the CRC/data
offsets to be placed anywhere in the file, there are no targets
which actually need this flexibility, because they are all using
plain old "scramble -add".

So we can actually simplify load_firmware() and remove defines
from the target headers. All the targets used CRC offset = 0 and
data offset = 8, except for a few which I assume never supported
ROLO or were never tested -- eg. samsungyh820: the CRC and data
offsets cannot both be 0.

The actual motivation for this is removing the calls to lseek(),
which can help make bootloaders a tiny bit smaller, as lseek is
typically not used anywhere else in bootloaders.

Change-Id: Ic2d01e5b75a32e88363f085e3e839146a0710bf4

1 files changed, 4 insertions, 5 deletions

diff --git a/firmware/common/rb-loader.c b/firmware/common/rb-loader.c
index 430ed6ec7b..0256f21884 100644
--- a/firmware/common/rb-loader.c
+++ b/firmware/common/rb-loader.c
@@ -58,16 +58,15 @@ static int load_firmware_filename(unsigned char* buf,
         goto end;
     }
 
-    lseek(fd, FIRMWARE_OFFSET_FILE_CRC, SEEK_SET);
-
-    if (read(fd, &chksum, 4) < 4)
+    /* read 32-bit checksum followed by 4-byte model name,
+     * this is the "scramble -add" header written by tools/scramble */
+    if (read(fd, buf, 8) < 8)
     {
         ret = EREAD_CHKSUM_FAILED;
         goto end;
     }
-    chksum = betoh32(chksum); /* Rockbox checksums are big-endian */
 
-    lseek(fd, FIRMWARE_OFFSET_FILE_DATA, SEEK_SET);
+    chksum = load_be32(buf); /* Rockbox checksums are big-endian */
 
     if (read(fd, buf, len) < len)
     {