Speed up Bus Pirate by exploiting the FTDI FIFO

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.
Thanks to Daniel Flinkmann for sponsoring development of this patch.
Tested-by: Daniel Flinkmann <DFlinkmann@gmx.de>

Corresponding to flashrom svn r1120.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Daniel Flinkmann <dflinkmann@gmx.de>

1 files changed, 22 insertions, 20 deletions

diff --git a/buspirate_spi.c b/buspirate_spi.c
index 97ce220..c56155f 100644
--- a/buspirate_spi.c
+++ b/buspirate_spi.c
@@ -260,8 +260,8 @@ int buspirate_spi_send_command(unsigned int writecnt, unsigned int readcnt,
 	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
@@ -269,39 +269,41 @@ int buspirate_spi_send_command(unsigned int writecnt, unsigned int readcnt,
 
 	/* 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 reading/writing SPI!\n");
+		msg_perr("Protocol error while lowering CS#!\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)
+	if (buf[1] != 0x01) {
+		msg_perr("Protocol error while reading/writing SPI!\n");
 		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;
 }