[flashrom] [PATCH] 3x speedup for Bus Pirate, violate protocol

[Carl-Daniel Hailfinger]

If we violate the raw SPI communication protocol requirements of the Bus
Pirate (namely, waiting for the completion of one command before sending
the next one), we can reduce the number of round trips by a factor of 3.
The FT2232 chip present in the Bus Pirate has a big enough buffer (at
least 128 bytes IIRC) to avoid overflows in the tiny buffer of the Bus
Pirate PIC.

Untested because I don't own the hardware.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006 at gmx.net>

Index: flashrom-buspirate_speedup_protocolviolation/buspirate_spi.c
===================================================================
--- flashrom-buspirate_speedup_protocolviolation/buspirate_spi.c	(Revision 1048)
+++ flashrom-buspirate_speedup_protocolviolation/buspirate_spi.c	(Arbeitskopie)
@@ -266,8 +266,8 @@
 	if (writecnt > 16 || readcnt > 16 || (readcnt + writecnt) > 16)
 		return SPI_INVALID_LENGTH;
 
-	/* +2 is pretty arbitrary. */
-	buf = realloc(buf, writecnt + readcnt + 2);
+	/* 3 bytes extra for CS#, len, CS#. */
+	buf = realloc(buf, writecnt + readcnt + 3);
 	if (!buf) {
 		msg_perr("Out of memory!\n");
 		exit(1); // -1
@@ -275,39 +275,41 @@
 
 	/* Assert CS# */
 	buf[i++] = 0x02;
-	ret = buspirate_sendrecv(buf, 1, 1);
-	if (ret)
-		return SPI_GENERIC_ERROR;
-	if (buf[0] != 0x01) {
-		msg_perr("Protocol error while lowering CS#!\n");
-		return SPI_GENERIC_ERROR;
-	}
 
-	i = 0;
 	buf[i++] = 0x10 | (writecnt + readcnt - 1);
 	memcpy(buf + i, writearr, writecnt);
 	i += writecnt;
 	memset(buf + i, 0, readcnt);
-	ret = buspirate_sendrecv(buf, i + readcnt, i + readcnt);
-	if (ret)
+
+	i += readcnt;
+	/* De-assert CS# */
+	buf[i++] = 0x03;
+
+	ret = buspirate_sendrecv(buf, i, i);
+
+	if (ret) {
+		msg_perr("Bus Pirate communication error!\n");
 		return SPI_GENERIC_ERROR;
+	}
+
 	if (buf[0] != 0x01) {
+		msg_perr("Protocol error while lowering CS#!\n");
+		return SPI_GENERIC_ERROR;
+	}
+
+	if (buf[1] != 0x01) {
 		msg_perr("Protocol error while reading/writing SPI!\n");
 		return SPI_GENERIC_ERROR;
 	}
-	memcpy(readarr, buf + i, readcnt);
 
-	i = 0;
-	/* De-assert CS# */
-	buf[i++] = 0x03;
-	ret = buspirate_sendrecv(buf, 1, 1);
-	if (ret)
-		return SPI_GENERIC_ERROR;
-	if (buf[0] != 0x01) {
+	if (buf[i - 1] != 0x01) {
 		msg_perr("Protocol error while raising CS#!\n");
 		return SPI_GENERIC_ERROR;
 	}
 
+	/* Skip CS#, length, writearr. */
+	memcpy(readarr, buf + 2 + writecnt, readcnt);
+
 	return ret;
 }
 


-- 
http://www.hailfinger.org/