[flashrom] [PATCH] FT2232 programmer frequency divider parameter support

[Samir Ibradžić]

Hello,

I would like to submit a patch, that enables extra argument when using 
FT2232 external programmer, a frequency divider. For FT2232 programmer 
we have this divider set to 3 by default by DIVIDE_BY constant, which 
will result in 10MHz (H-chips) or 2MHz (non H-chips) SPI speeds.

By providing divider as parameter, SPI interface frequency culd be 
overridden by user, resulting in different speeds (H-chip example):

  divider |  freq
---------+--------
     1    |  30Mhz
     2    |  15Mhz
     3    |  10Mhz
     4    | 7.5Mhz
     5    |  6Mhz
     6    |  5Mhz
    15    |  2Mhz
    30    |  1Mhz
    60    | 0.5Mhz
   600    | 0.05Mhz
    (and so on)

These lower than default SPI speeds can be very useful when we have 
flawed flash chips that would not support 10Mhz or bad quality or too 
long cabling between programmer and the chip. Higher than default speeds 
might also be useful (if only flashrom AAI implementation was faster).

Please note that this parameter is arbitrary integer, maybe only a value 
up to 255 would really make sense, but i can not be sure about that 
since it may be programmer hardware dependent. All values between 1-255 
worked for me (PicoTAP programmer), as well as 300 & 600 (these resulted 
in extremely slow flash reads, as expected, 2MB flash that usually takes 
16s to read @2-10Mhz, took more than 6 minutes @0.05Mhz). Others values 
i haven't tested.

Signed-off-by: Samir Ibradžić <sibradzic at gmail.com>
---
$ svn diff
Index: ft2232_spi.c
===================================================================
--- ft2232_spi.c	(revision 1451)
+++ ft2232_spi.c	(working copy)
@@ -168,6 +168,7 @@
  	enum ftdi_interface ft2232_interface = INTERFACE_B;
  	char *arg;
  	double mpsse_clk;
+	int divider = DIVIDE_BY;	

  	arg = extract_programmer_param("type");
  	if (arg) {
@@ -237,6 +238,17 @@
  		}
  	}
  	free(arg);
+	arg = extract_programmer_param("divider");
+	if (arg) {
+		if (isdigit(*arg) && (atoi(arg) > 0))
+			divider = atoi(arg);
+		else {
+			msg_perr("Error: Invalid frequency divider specified.\n");
+			free(arg);
+			return -2;
+		}
+	}
+	free(arg);
  	msg_pdbg("Using device type %s %s ",
  		 get_ft2232_vendorname(ft2232_vid, ft2232_type),
  		 get_ft2232_devicename(ft2232_vid, ft2232_type));
@@ -298,16 +310,16 @@
  	msg_pdbg("Set clock divisor\n");
  	buf[0] = 0x86;		/* command "set divisor" */
  	/* valueL/valueH are (desired_divisor - 1) */
-	buf[1] = (DIVIDE_BY - 1) & 0xff;
-	buf[2] = ((DIVIDE_BY - 1) >> 8) & 0xff;
+	buf[1] = (divider - 1) & 0xff;
+	buf[2] = ((divider - 1) >> 8) & 0xff;
  	if (send_buf(ftdic, buf, 3)) {
  		ret = -6;
  		goto ftdi_err;
  	}

  	msg_pdbg("MPSSE clock: %f MHz divisor: %d "
-		 "SPI clock: %f MHz\n", mpsse_clk, DIVIDE_BY,
-		 (double)(mpsse_clk / (((DIVIDE_BY - 1) + 1) * 2)));
+		 "SPI clock: %f MHz\n", mpsse_clk, divider,
+		 (double)(mpsse_clk / (((divider - 1) + 1) * 2)));

  	/* Disconnect TDI/DO to TDO/DI for loopback. */
  	msg_pdbg("No loopback of TDI/DO TDO/DI\n");
--
R,
S