Explain the index/value format baudrate setting

test/baudrate.cpp: Evaluate according to this explanation

diff --git a/src/ftdi.c b/src/ftdi.c
index 66c159e..0c8d540 100644 (file)
--- a/src/ftdi.c
+++ b/src/ftdi.c
@@ -1069,6 +1069,18 @@ static int ftdi_to_clkbits_AM(int baudrate, unsigned long *encoded_divisor)
    clk/2   -> 2
    From /2, 0.125 steps may be taken.
    The fractional part has frac_code encoding
+
+   value[13:0] of value is the divisor
+   index[9] mean 12 MHz Base(120 MHz/10) rate versus 3 MHz (48 MHz/16) else
+
+   H Type have all features above with
+   {index[8],value[15:14]} is the encoded subdivisor
+
+   FT232R, FT2232 and FT232BM have no option for 12 MHz and with 
+   {index[0],value[15:14]} is the encoded subdivisor
+
+   AM Type chips have only four fractional subdivisors at value[15:14]
+   for subdivisors 0, 0.5, 0.25, 0.125
 */
 static int ftdi_to_clkbits(int baudrate, unsigned int clk, int clk_div, unsigned long *encoded_divisor)
 {

diff --git a/test/baudrate.cpp b/test/baudrate.cpp
index 0d2e0b8..7ce2e9a 100644 (file)
--- a/test/baudrate.cpp
+++ b/test/baudrate.cpp
@@ -87,10 +87,24 @@ static void test_baudrates(ftdi_context *ftdi, const map<int, calc_result> &baud
 
         const calc_result *res = &baudrate.second;
 
-        unsigned short divisor = calc_value & 0x3ff;
-        unsigned short fractional_bits = (calc_index & 0x100) ? 4 : (calc_value >> 12);
-        unsigned short clock = (calc_index & 0x100) ? 120 : 48;
-
+        unsigned short divisor = calc_value & 0x3fff;
+        unsigned short fractional_bits = (calc_value >> 14);
+        unsigned short clock = (calc_index & 0x200) ? 120 : 48;
+
+        switch (ftdi->type)
+        {
+        case TYPE_232H:
+        case TYPE_2232H:
+        case TYPE_4232H:
+            fractional_bits |= (calc_index & 0x100) ? 4 : 0;
+            break;
+        case TYPE_R:
+        case TYPE_2232C:
+        case TYPE_BM:
+            fractional_bits |= (calc_index & 0x001) ? 4 : 0;
+            break;
+        default:;
+        }
         // Aid debugging since this test is a generic function
         BOOST_CHECK_MESSAGE(res->actual_baudrate == calc_baudrate && res->divisor == divisor && res->fractional_bits == fractional_bits
                             && res->clock == clock,