From 104c29feaeee40e94580b952b8cf793d54727612 Mon Sep 17 00:00:00 2001
From: oharboe <oharboe>
Date: Fri, 10 Oct 2008 07:07:57 +0000
Subject: a few words about the ZY1000 ZPU JTAG debugger

---
 zpu/docs/zpu_arch.html | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/zpu/docs/zpu_arch.html b/zpu/docs/zpu_arch.html
index e7cf30c..7ddbea7 100644
--- a/zpu/docs/zpu_arch.html
+++ b/zpu/docs/zpu_arch.html
@@ -23,6 +23,7 @@ $id$
 <li> <a href="#performance">Speeding up the ZPU</a>
 <li> <a href="#debuguart">Debug channel / UART</a>
 <li> <a href="#wishbone">Wishbone</a>
+<li> <a href="#hwdebugger">JTAG/hardware debugger for GDB</a>
 <li> <a href="#zpu_core_small.vhd">About zpu_core_small.vhd</a>
 <li> <a href="#zpu_core.vhd">About zpu_core.vhd</a>
 <li> <a href="#zealot">Zealot: Implementing in FPGAs</a>
@@ -1481,6 +1482,29 @@ of the ZPU, which differs slightly from <a href="../hdl/zpu4/core" target="_blan
 <p>
 The ZY2000 is a complete implementation of the ZPU including: DRAM, soft-MAC, wishbone bridges, GPIO subsystem,
 etc. This also included an eCos HAL w/TCP/IP support.
+
+<a name="hwdebugger"/>
+<h1>JTAG/hardware debugger for GDB</h1>
+The Zylin <a href="http://www.zylin.com/zy1000.html">ZY1000</a> JTAG debugger supports
+the ZPU. Contact <a href="http://www.zylin.com">Zylin</a> for pricing and details.
+<p>
+There are two debug modes in which the ZY1000 can operate:
+<ul>
+<li>Classic. Here the ZY1000 controls the CPU and examines the state. The ZY1000 has a built in
+GDB server that GDB talks to.
+<li>Small footprint. If there isn't enough space on the device for the ZPU *and* the JTAG
+controller, then the ZY1000 can run the ZPU externally. The JTAG communication channel is
+then used to peek/poke peripherals and inside the FPGA instead of the ZPU there is then
+a JTAG controller that peeks and pokes the peripherals of the ZPU. There are advantages
+and disadvantages of this approach: it may be unfamiliar to embedded developers and  
+the timing is different from the "real" ZPU(interrupts are delayed, execution speed
+differse, etc.) On the other hand there are other things
+which are simpler: much more RAM can be available for the ZPU during development,
+better debug consoles(faster), additional peripheral(timers, etc.) is available. This
+approach is somewhat unique to the ZPU as the ZPU is simple enough that it can be
+implemented efficiently in this manner. 
+</ul>
+
 <a name="interrupts"/>
 <h1>Interrupts</h1>
 The ZPU supports interrupts.
-- 
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