asix-sigma: Document sampling rate table

Add comments to the sampling rate table explaining how the frequencies
are selected and where do those numbers come from.

Signed-off-by: Marek Vasut <redacted>

diff --git a/hardware/asix-sigma/asix-sigma.c b/hardware/asix-sigma/asix-sigma.c
index 1c8e04bdad08f8315908e31efe38adcdb5a05286..d17558d4e18d294b8c66d216f72b2707f4ad10ab 100644 (file)
--- a/hardware/asix-sigma/asix-sigma.c
+++ b/hardware/asix-sigma/asix-sigma.c
@@ -43,17 +43,23 @@ SR_PRIV struct sr_dev_driver asix_sigma_driver_info;
 static struct sr_dev_driver *di = &asix_sigma_driver_info;
 static int dev_acquisition_stop(struct sr_dev_inst *sdi, void *cb_data);
 
+/*
+ * The ASIX Sigma supports arbitrary integer frequency divider in
+ * the 50MHz mode. The divider is in range 1...256 , allowing for
+ * very precise sampling rate selection. This driver supports only
+ * a subset of the sampling rates.
+ */
 static const uint64_t samplerates[] = {
-       SR_KHZ(200),
-       SR_KHZ(250),
-       SR_KHZ(500),
-       SR_MHZ(1),
-       SR_MHZ(5),
-       SR_MHZ(10),
-       SR_MHZ(25),
-       SR_MHZ(50),
-       SR_MHZ(100),
-       SR_MHZ(200),
+       SR_KHZ(200),    /* div=250 */
+       SR_KHZ(250),    /* div=200 */
+       SR_KHZ(500),    /* div=100 */
+       SR_MHZ(1),      /* div=50  */
+       SR_MHZ(5),      /* div=10  */
+       SR_MHZ(10),     /* div=5   */
+       SR_MHZ(25),     /* div=2   */
+       SR_MHZ(50),     /* div=1   */
+       SR_MHZ(100),    /* Special FW needed */
+       SR_MHZ(200),    /* Special FW needed */
 };
 
 /*