X-Git-Url: http://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/2da2e9283771f20e4fb809709ea1c97c0636e455..f9c1dcd9f6e68a8c07cffed697a9c4c8caed6015:/armsrc/util.c

diff --git a/armsrc/util.c b/armsrc/util.c
index 8576ddce..be41bad8 100644
--- a/armsrc/util.c
+++ b/armsrc/util.c
@@ -304,11 +304,12 @@ void FormatVersionInformation(char *dst, int len, const char *prefix, void *vers
 
 void StartTickCount()
 {
-//  must be 0x40, but on my cpu - included divider is optimal
-//  0x20 - 1 ms / bit 
-//  0x40 - 2 ms / bit
-
-	AT91C_BASE_RTTC->RTTC_RTMR = AT91C_RTTC_RTTRST + 0x001D; // was 0x003B
+	// This timer is based on the slow clock. The slow clock frequency is between 22kHz and 40kHz.
+	// We can determine the actual slow clock frequency by looking at the Main Clock Frequency Register.
+    uint16_t mainf = AT91C_BASE_PMC->PMC_MCFR & 0xffff;		// = 16 * main clock frequency (16MHz) / slow clock frequency
+	// set RealTimeCounter divider to count at 1kHz:
+	AT91C_BASE_RTTC->RTTC_RTMR = AT91C_RTTC_RTTRST | ((256000 + (mainf/2)) / mainf);
+	// note: worst case precision is approx 2.5%
 }
 
 /*
@@ -430,3 +431,19 @@ uint32_t RAMFUNC GetCountSspClk(){
 	}
 }
 
+static uint64_t next_random = 1;
+
+/* Generates a (non-cryptographically secure) 32-bit random number.
+ *
+ * We don't have an implementation of the "rand" function or a clock to seed it
+ * with, so we just call GetTickCount the first time to seed ourselves.
+ */
+uint32_t prand() {
+	if (next_random == 1) {
+		next_random = GetTickCount();
+	}
+
+	next_random = next_random * 6364136223846793005 + 1;
+	return (uint32_t)(next_random >> 32) % 0xffffffff;
+}
+