Transactional logic, mostly done outgoing, structured incoming. Split tract and...

[firmerware] / src / driver / tic55x / timer.c

diff --git a/src/driver/tic55x/timer.c b/src/driver/tic55x/timer.c
index c394fb7..083e74e 100644 (file)
--- a/src/driver/tic55x/timer.c
+++ b/src/driver/tic55x/timer.c
@@ -66,6 +66,11 @@
 
 static timing_t current_timer = 0;
 
+#define ENTROPY_BUFLEN 17
+static uint8_t entropy_pseudo [ENTROPY_BUFLEN];
+static uint8_t entropy_wpos = 0;
+static uint8_t entropy_rpos = 0;
+
 
 /* Read the current time from timer1's top part.  Be careful about
  * timer increments between the two word reads.
@@ -135,6 +140,29 @@ interrupt void tic55x_tint0_isr (void) {
 }
 
 
+/* Read the lower-half timer for a bit of entropy, at a time
+ * deemed appropriate by the top half.
+ */
+void bottom_rndseed (void) {
+       entropy_pseudo [entropy_wpos++] ^= GPTCNT3_1 & 0xff;
+       if (entropy_wpos >= ENTROPY_BUFLEN) {
+               entropy_wpos = 0;
+       }
+}
+
+/* Retrieve a given number of random bytes from the entropy
+ * buffer.
+ */
+void bottom_rnd_pseudo (uint8_t *rnd, uint8_t len) {
+       while (len-- > 0) {
+               *rnd++ = entropy_pseudo [entropy_rpos += 4];
+               if (entropy_rpos >= ENTROPY_BUFLEN) {
+                       entropy_rpos -= ENTROPY_BUFLEN;
+               }
+       }
+}
+
+
 /* Setup timers and the corresponding interrupts for timer0/timer1
  */
 void tic55x_setup_timers (void) {