diff --git a/attn/Attention_Handler.md b/attn/Attention_Handler.md
index 45502ba..c44114c 100644
--- a/attn/Attention_Handler.md
+++ b/attn/Attention_Handler.md
@@ -1,56 +1,184 @@
-# Hardware Error Attention Handling for POWER Systems
+# Introduction
 
-Attentions are host error and debug breakpoint conditions that can be handled
-by software running on the BMC. The host alerts the BMC of these conditions
-via the Attention GPIO pin. The Attention Handler application (ATTN) monitors
-this gpio for activity and services active attentions. When activity is
-detected on the Attention GPIO, ATTN will query the hardware to determine the
-active attention that needs to be serviced.
+An attention is a hardware, firmware or software alert mechanism used to
+request service from an Attention Handler via an attention signal (e.g. a
+GPIO). An attention handler is, in this case, a stateless service that handles
+attention requests. The attention handler in combination with a hardware
+analyzer constitutes the Openpower Hardware Diagnostics (hardware diags)
+component. Hardware diags can operate in daemon mode and in application mode.
+When operating in daemon mode openpower hardware diags may be referred to as
+the attention handler or attention handler service. When operating in
+application mode openpower hardware diags may be referred to as the analyzer.
+Both modes executing simultaneously is supported however. There can be at most
+one instance of the attention handler service, per attention signal.
 
-## Attention Handler Logic
-The following logic is implemented in ATTN to allow for controlling the flow
-of attention handling once an attention event has been detected.
+# Overview
 
-- ATTN can adjust the handling priority of active attention events.
+The main role of the attention handler is a long running process monitoring the
+attention interrupt signal and delegating tasks to external components to aid
+in handling attention requests. The attention handler is loaded into memory
+when the host is started and monitors the attention signal until the host is
+stopped. When an attention (signal) is detected by the attention handler
+(monitor) the attention handler will query the state of the host to determine
+the nature of the active attention(s).
 
-- ATTN can choose to defer or ignore handling of attention events.
+The attention handler services four types of attentions namely, and in order of
+priority, Vital Attention (vital), Terminate Immediately (TI), Breakpoint
+Attention (BP) and Checkstop Attention (checkstop). TI and BP attentions are
+categorically called Special Attentions (special) and are mutually exclusive.
+Additionally a TI can be raised by either hostboot (HBTI) or the hypervisor
+(PHYPTI).
 
-- ATTN can handle any number of active attentions per GPIO event.
+The general handling of attentions is as follows:
+- vital: log an event, request a SBE dump and request a re-ipl of the host.
+- PHYPTI: log an event and request a memory preserving IPL (MPIPL) of the host.
+- HBTI: log an event, request a hardware dump and request a re-ipl of the host.
+- BP: notify the debug agent (e.g. Cronus)
+- checkstop: log an event, call the analyzer, request a system dump and request
+  a re-ipl of the host. 
 
-- ATTN can continue monitoring or stop monitoring the attention GPIO.
+# Implementation Details
 
-## Attention Conditions
-The following is a list of attention conditions and actions.
+## External Components
 
-1. SBE Attention (vital): This attention indicates that the SBE is in a state
-   that is considered non-functional. ATTN will log this event and *...TBD*
+The attention handler relies on several external components and BMC services
+for the handling of attentions. Among these are systemd, dbus, phosphor-logging
+and PDBG.
 
-2. System Checkstop (checkstop): This attention indicates an error condition
-   in which the host cannot continue operating properly. ATTN will launch the
-   Hardware Diagnostics application (Hwdiags) and may provide Hwdiags with
-   information needed to help it analyze the checkstop *...TBD*
+The general use of these components are as follows:
+- systemd: loading and unloading of the attention handler service.
+- dbus: querying the state of the BMC and host, requesting dumps and requesting
+  host IPL's
+- phosphor-logging: debug tracing and logging platform events.
+- PDBG: querying host hardware.
 
-3. Special Attention (special): This attention indicates that one of the
-   following conditions has occurred.
+## Component Usage
 
-    - PHYP Breakpoint (breakpoint): ATTN will send notification with the
-      processor, core and thread number associated with the event.
+- Platform Event Log (PEL) entry creation and debug tracing: phosphor-logging
+  component.
+- Host Transition (re-IPL, MPIPL request): dbus interface.
+- Attention handler starting and stopping: systemd. 
 
-    - PHYP Terminate Immediate (PHYP TI): ATTN will dump and re-ipl.
+## Starting and Stopping
 
-    - OPAL Terminate Immediate (OPAL TI): ATTN will dump and re-ipl.
+The attention handler service is started via the BMC systemd infrastructure
+when the host is started. When the attention handler is started it will
+register itself as the GPIO event handler associated with the attention GPIO
+and remain resident in memory waiting for attentions. The attention handler
+will be stopped via the BMC systemd infrastructure when the host is stopped.
 
-    - Core Code to SP (PHYP CoreCode): ATTN will log this event.
+If the attention handler terminates due to an error condition it will
+automatically be restarted by systemd. The attention handler restart policy is
+based on the BMC default restart policy (n-number of restarts in n-seconds
+maximum).
 
-    - Other (instruction stop, core recovery handshake): Attention will log
-      these events.
+## Attentions
 
-##Command Line Interface
+When the attention signal becomes active the attention handler will begin
+handling attentions. Using the PDBG interface the attention handler will query
+the host to determine the reason for the active attention handler signal.  Each
+enabled processor will be queried and a map of active attentions will be
+created. The first attention of highest priority will be the one that is
+serviced (see Overview for attention type and priority). The Global Interrupt
+Status Register in combination with an associated attention mask register is
+used to determine active attentions.
 
-ATTN supports the following command line interface *...TBD*
+### Vital Attention
 
-##Building
+A vital attention is handled by generating an event log via the
+phosphor-logging inteface and then using the dump manager dbus interface to
+request a hardware dump. The attention handler will wait, up to one hour, for
+the dump to complete and then use the systemd interface to request a re-IPL of
+the host. This type of attention indicates that there was a problem with the
+Self Boot Engine (SBE) hardware.
 
-This application is built using the standard Meson/Ninja build setup.
+### Special Attentions
 
-    meson build && cd build && ninja
+Three types of attentions, HBTI, PHYPTI and BP, share a single attention status
+flag (special attention) in the global interrupt status register. In order to
+determine the specific type of special attention the attention handler relies
+on a portion of shared memory called the Shared TI Information Data Area (TI
+info). The attention handler gains access to this memory region by submitting a
+request for its memory address through the PDBG interface. The request is via a
+Chip Operation (chipop) command. 
+
+#### HBTI
+
+These attention types are indications from hostboot that an error has occurred
+or a shutdown has been requested. When servicing a HBTI the attention handler
+will consider two cases namely a TI with SRC and a TI with EID.
+
+For a TI with SRC, using the TI info,  the attention handler will create and
+submit a PEL entry on behalf of hostboot, request a hostboot dump and upon
+completion, or timeout, request a re-IPL of the host using the dbus interface.
+Optionally, based upon flags in the TI info, the attention handler may mark the
+PEL entry as hidden.
+
+For a TI with EID, the attention handler will, based upon flags in the TI info,
+request a hostboot dump using the dbus interface. Upon completion, or timeout,
+of the dump the attention handler will request a re-IPL of the host via the
+dbus interface. For a TI with EID the attention handler will forgo creating a
+PEL entry (hostboot has already done this).
+
+#### PHYPTI
+
+These attentions are indications from the hypervisor that an error has
+occurred. When servicing a PHYPTI the attention handler will generate a PEL
+entry and then request a host MPIPL using the PDBG interface (chipop).
+
+#### BP (breakpoint)
+
+These attentions are used to signal to the attention handler that it should
+notify the debug agent (e.g. Cronus) that a debug breakpoint has been
+encountered. If the TI info data is considered valid and neither a HBTI or
+PHYPTI is determined to be the cause of the special attention then a BP
+attention is assumed. When a BP attention occurs the attention handler will use
+the dbus interface to notify the debug agent that a breakpoint condition was
+encountered. The attention handler will then go back to listening for
+attentions.
+
+#### Recoverables
+
+These attentions are indications that recoverable errors have been encountered.
+These attentions do not generate an attention GPIO event however when servicing
+a TI the attention handler will note whether or not the host is reporting
+recoverable errors. If recoverable errors are present the attention handler
+will call the analyzer before requesting a dump or IPL. The check for
+recoverable errors is done using the PDBG interface (the Global Interrupt
+Status Register).
+
+### Checkstop
+
+These attentions indicate that a hardware error has occurred and further
+hardware analyses is required to determine root cause. When servicing a
+checkstop attention the attention handler will call the analyzer and then wait
+for analyses to complete. Once analyses have completed the attention handler
+will use the dbus interface to request a system dump and upon completetion, or
+timeout, will request a re-IPL of the host.
+
+## Configuration
+
+Some attention handler behavior can be configured by passing parameters to the
+service using the service file or using the command line. Currently the
+following behaviors are configurable:
+- vital handling enable/disable, default enable
+- TI handling enable/disable, default enable
+- BP handling enable/disable, default enable
+- checkstop handling enable/disable, default enable
+- special attention default BP/TI, default BP
+
+## Additional Considerations
+
+Regardless of the type of special attention the attention handler will always
+create at least one PEL entry containing attention handler specific FFDC. In
+some cases this entry may be informational.
+
+Regardless of the type of attention, after servicing the attention the
+attention handler will return to listening for attentions. In most cases no
+more attentions will be detected unless the currently active attentions are
+cleared. Normally active attentions will be cleared by the host re-IPL but any
+component could clear the active attentions as is the case for BP attentions
+and the debug agent.
+
+If the attention handler encounters any errors while servicing an interrupt it
+will generate a PEL entry to indicate the error that was encountered.