From: lkcl <lkcl@web>
Date: Sun, 14 Nov 2021 18:15:53 +0000 (+0000)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~3390
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=1855519e9697626612d224151ad6f2974c3121f3;p=libreriscv.git

---

diff --git a/docs/pinmux.mdwn b/docs/pinmux.mdwn
index 462bc05dc..1d340f226 100644
--- a/docs/pinmux.mdwn
+++ b/docs/pinmux.mdwn
@@ -100,6 +100,19 @@ but it can also read or control the Core (peripheral).
 This is its entire purpose: to allow for the detection
 and triaging of faults.
 
+* Software may be uploaded and run which sets a bit on
+  one of the peripheral outputs (UART Tx for example).
+  If the UART TX IO Pad was faulty, no possibility existd
+  without Boundary Scan to determine if the peripheral
+  was at fault.  With the UART TX pin function being
+  redirected to a JTAG Shift Register, the results of the
+  software setting UART Tx may be detected by checking
+  the appropriate Shift Register bit.
+* Likewise, a voltage may be applied to the UART RX Pad,
+  and the corresponding SR bit checked to see if the
+  pad is working.  If the UART Rx peripheral was faulty
+  this would not be possible.
+
 <img src="https://libre-soc.org/shakti/m_class/JTAG/jtag-block.jpg"
   width=500 />